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Universidad Nacional Autónoma de México
Centro de Geociencias
Programa de Posgrado en Ciencias de la Tierra
Estudio de la Geoquímica, la Estructura y el
Metamorfismo en el Este del Complejo
Acatlán: Implicaciones Tectonicas y
Paleogeograficas
——
Continental arc development along the periphery of
Pangea: Late Paleozoic pluton emplacement and basin
evolution in a transtensional setting, eastern Acatlán
Complex, Mexico
Moritz Kirsch
Tesis sometida en cumplimiento parcial
de los requisitos para el grado de
Doctor en Ciencias de la Tierra
ASESORES:
Dr. J. Duncan Keppie
Dr. J. Brendan Murphy
Juriquilla, Qro, México
JURADO EXAMINADOR:
Dra. Elena Centeno-García
Dr. Peter Schaaf
Dr. J. Duncan Keppie
Dr. Luca Ferrari
Dr. Michelangelo Martini
Agosto, 2012
Moritz Kirsch: Estudio de la Geoquímica, la Estructura y el Metamorfismo en
el este del Complejo Acatlán: Implicaciones Tectonicas y Paleogeograficas, Tesis
c Agosto, 2012
Doctoral En memoria cariñosa de mis abuelos Otto y Ruth Kirsch, y mi abuelo
Siegfried Schröder.
RESUMEN
En el sector este del Complejo Acatlán, sur de México, se encuentra un
conjunto de rocas de edad Paleozoico tardío, compuesto por un cuerpo intrusivo de la asamblea gabro-diorita-tonalita-trondhjemita (plutón Totoltepec) y una secuencia clástica-calcárea de bajo grado de metamorfismo (formación Tecomate). Estas rocas fueron emplazadas y depositadas después
de la orogenia colisional asociada a la formación de Pangea. Por lo tanto, el
área de estudio ofrece la oportunidad de investigar procesos geológicos en
diferentes niveles corticales de un arco magmático en la periferia de Pangea
durante el tiempo crucial entre amalgación y rotura del supercontinente.
El plutón Totoltepec con una superficie de afloramiento de 15 × 5 km está
limitado por dos fallas Pérmicas dextrales con orientación N–S, al sur por
una cabalgadura E–W con buzamiento norte, y al norte por una falla normal
E–W. El plutón está compuesto por rocas máficas–ultramáficas subordinadas (306 ± 2 Ma; análisis concordante de U-Pb en circón) que afloran en
el margen de la intrusión máfica–felsica principal (289 ± 2 Ma). La geoquímica de las rocas marginales muestra una afinidad toleítica a calco-alcalina
con alto LILE/HFSE (elementos litófilos de radio iónico grande/elementos
de alto potencial iónico), tierras raras de espectro plano y valores iniciales
de Nd entre +1.3 y +3.3. Los elementos traza de la fase plutónica más
joven describen una afinidad calco-alkalina con espectros de tierras raras
moderadamente fraccionados y valores iniciales de Nd entre -0.8 a +2.6,
lo cual también sugiere un ambiente de arco para su formación. Datos termobarométricos indican que el cuerpo principal del plutón fue emplazado
a 620 km de profundidad y una temperatura de >700 ◦ C, y fue exhumado
a 11 km y 400 ◦ C en 4 ± 2 Ma. Se ha documentado la siguiente secuencia
intrusiva: (i) la fase máfica del margen norte de 306 Ma, (ii) la fase principal
trondhjemítica de 287 Ma, y (iii) diques subverticales de approx. 289–283
Ma que varian desde (a) N39◦ E, no-deformados con crecimiento de cristales perpendiculares a las márgenes, a (b) approx. N50–73◦ E, foliados y
plegados con indicadores cinemáticos sinistrales, hasta (c) N73–140◦ E con
estructuras tipo boudinage. La obliquidad del límite entre los diques plegados y estirados en relación a fallas dextrales de rumbo N-S sugiere un
emplazamiento secuencial en un ambiente transtensional con 20 % de extensión con dirección E-W, pasando por un campo de acortamiento bajo
diferentes grados de rotación en sentido horario, acompañado por cizallamiento lateral izquierdo, a un campo de extensión. La intrusión de approx.
289–287 Ma contiene una foliación subvertical de rumbo ENE y un lineamiento que varia de subhorizontal a muy inclinada, probablemente debido
al emplazamiento en un ambiente de deformación triclínica. Se infiere que
el magmatismo cesó cuando un componente de movimiento fue transferido
de la falla del límite occidental a la falla del límite oriental, resultando en
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un cabalgamiento a lo largo del límite sur del plutón. Este mecanismo puede explicar el rápido levantamiento y exhumación del plutón entre approx.
287 y 283 Ma.
La formación Tecomate se define actualmente como un compuesto de
unidades de litología similar, depositadas desde el Carbonífero hasta el Pérmico en múltiples cuencas limitadas por fallas. Al sur del plutón Totoltepec,
la edad de depositación de la formación Tecomate está bien definida en ∼300
Ma en una sección, y entre ∼288 y ∼263 Ma en otra. Las rocas de la formación Tecomate están interpretadas como derivados de un arco magmático
del Paleozoico tardío, basandose en (i) su geoquímica de afinidad de arco,
(ii) valores Nd(t) entre -5.6 a +0.3 (t = 288 Ma) que traslapan los del plutón Totoltepec, y (iii) una población dominante de circones con edades que
varian de Carbonífero a Pérmico. Las unidades de Totoltepec y Tecomate
en el área de estudio forman parte de un arco continental que se extiende
desde Guatemala hasta California, lo cual implica subducción del paleoPacífico bajo el margen occidental en una configuración paleogeográfica de
Pangea-A.
ABSTRACT
In the eastern Acatlán Complex of southern Mexico, a Late Paleozoic
assemblage comprising a gabbro-diorite-tonalite-trondhjemite suite (Totoltepec pluton) and clastic-calcareous metasedimentary rocks (Tecomate Formation), post-dates collisional orogeny that resulted in the amalgamation
of Pangea. This region offers a rare opportunity to examine assemblages
developed at different crustal levels of a magmatic arc along the periphery
of Pangea at the critical stage between amalgamation and breakup.
The 15 x 5 km Totoltepec pluton is bounded by two N–S Permian dextral faults, an E–W thrust to the south, and an E–W normal fault to the
north. The pluton consists of minor mafic–ultramafic rocks (306 ± 2 Ma;
concordant U-Pb zircon analysis) that are marginal to the main mafic–felsic
intrusion (289 ± 2 Ma). Geochemistry of the marginal rocks indicates an
arc tholeiitic to calc-alkaline character with high LILE/HFS, flat REE patterns and initial Nd values of +1.3 to +3.3. The younger Totoltepec phase
exhibits a calc-alkaline trace element geochemistry with flat to moderately
fractionated LREE enriched patterns, and initial Nd values of -0.8 to +2.6,
which are also consistent with an arc environment. Thermobarometric data
indicate that the main, ca. 289–287 Ma part of the pluton was emplaced at
620 km depth and >700 ◦ C, and was exhumed to 11 km and 400 ◦ C in 4
± 2 Ma. The following intrusive sequence is documented: (i) the 306 Ma
northern marginal mafic phase; (ii) the 287 Ma main trondhjemitic phase;
and (iii) ca. 289–283 Ma subvertical dikes that vary from (a) N39◦ E, undeformed with crystal growth perpendicular to the margins, through (b) ca.
N50–73◦ E, foliated and folded with sinistral shear indicators, to (c) N73–
140◦ E and boudinaged. The obliquity of the boundary between the folded
v
and stretched dikes relative to the N-S dextral faults suggests sequential emplacement in a transtensional regime (with 20 % E–W extension), followed
by different degrees of clockwise rotation passing through a shortening field
accompanied by sinistral shear into an extensional field. The ca. 289–287 Ma
intrusion also contains a steep ENE-striking foliation, and hornblende lineations varying from subhorizontal to steeply plunging, probably the result of
emplacement in a triclinic strain regime. We infer that magmatism ceased
when some of the dextral motion was transferred from the western to the
eastern bounding fault, causing thrusting to take place along the southern
boundary of the pluton. This mechanism is also invoked for the rapid uplift
and exhumation of the pluton between ca. 287 and 283 Ma.
The Tecomate Formation, as currently defined, is a composite of lithologically similar strata deposited in several fault-bounded basins ranging from
Carboniferous to Early Permian in age. To the south of the Totoltepec pluton, the depositional age of the Tecomate Formation is tightly constrained in
one section to ∼300 Ma but in another section it is between ∼288 and ∼263
Ma. The Tecomate Formation rocks are interpreted to have been derived
from a Late Paleozoic arc based on (i) its arc-related geochemistry, (ii) Nd(t)
values ranging from -5.6 to +0.3 (t = 288 Ma) that overlap those of the Totoltepec pluton, and (iii) detrital zircons with predominantly Carboniferous–
Permian ages. The Totoltepec and Tecomate units in the study area form
part of a continental arc extending from Guatemala to California, which
necessitates subduction of the paleo-Pacific oceanic lithosphere beneath the
western margin of a Pangea-A configuration.
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Oh du schönes, o du wunderschönes,
uraltes, sagen- und liederreiches Land Mexiko!
Desgleichen gibt es nicht wieder auf dieser Erde.
— B. Traven
AGRADECIMIENTOS
Me gustaría reconocer a J. Duncan Keppie y J. Brendan Murphy por su
supervisión, paciencia, motivación y financiación. Me siento tremendamente afortunado de haber tenido la oportunidad de venir a México y trabajar con ustedes. Además de la geología espectacular que me tocó estudiar,
realmente fue una experiencia cultural, tal como se había prometido. He
aprendido mucho de ustedes dos en estos cuatro años—Brendan, me enseñaste la importancia de principios y procesos en la redacción científica, no
perder nunca vista del panorama completo, hacer mil cosas al mismo tiempo, mantener impulso, estar pendiente de muestras y atar cabos sueltos, ser
articulado y organizado. Duncan, tu experiencia geológica y sentido de la
orientación en el campo, tu humor, tu parsimonia y eficiencia en todas las
cuestiones científicas y burocráticas eran una verdadera inspiración. Estoy
convencido de que me han preparado bien para una carrera como geólogo
hard-rock.
Además de los asesores de mi tesis, quisiera dar las gracias a todas las
demás personas que han contribuido de una manera u otra a este trabajo.
Maria Helbig, Mario A. Ramos-Arias, Gonzalo Galaz, y Domingo Schievenini donaron su tiempo y esfuerzo para asistirme en el campo y ayudarme con la preparación de muestras. Luigi Solari, Consuelo Macías Romo,
Carlos Linares, Carlos Ortega-Obregón, Ofelia Pérez-Arvizu, Aldo Izaguirre, Alex Iriondo, y Harald N. Böhnel brindaron asistencia invaluable en
el laboratorio. He beneficiado mucho de la colaboración y las conversaciones inspiradoras con Maria Helbig, Luigi Solari, James K. W. Lee, Fraser
Keppie, Uwe Kroner, Fernando Ortega-Gutiérrez, R. Damien Nance, Cecilio
Quesada, Roberto S. Molina-Garza, Barbara M. Martiny, James Sears, Chris
Smith, y Axel Renno. También me gustaría agradecer a los miembros de mi
comité tutoral: Luigi Solari, Fernando Ortega-Gutiérrez, Duncan Keppie,
y Brendan Murphy, así como el comité de mi examen predoctoral: Elena
Centeno-García, Peter Schaaf, Gustavo Tolson, y Dante J. Morán Zenteno
por su tiempo y el asesoramiento profesional. Peter Schaaf, Bodo Weber,
Luca Ferrari, W. Gary Ernst, y dos revisores anónimos son reconocidos por
proporcionar revisiones constructivas de los manuscritos de los artículos
que forman parte de esta tesis. Gracias a Roberto S. Molina-Garza y María
Clara Zuluaga Velez por tomarse el tiempo para corregir la versión española
de la tesis.
Deseo extender un agradecimiento especial a la secretaria académica Marta Pereda Miranda y la abogada Lic. Ana Paola González Cruz del Centro
vii
de Geociencias. Sin su ayuda competente me hubiera perdido en la jungla
de la burocracia académica.
Agradezco al Consejo Nacional de Ciencia y Tecnología y a la Dirección
General de Estudios de Posgrado de la UNAM por las becas otorgadas
para la realización de mis estudios de doctorado. Además agradezco la
Coordinación de Posgrado por el apoyo financiero brindado en la impresión
de la tesis.
Por último, deseo expresar mi profundo y sincero agradecimiento a mis
padres, Bettina y Frank-Michael, y sus respectivas parejas Michael Freitag
y Heike Kirsch, mi hermana Steffi, mis abuelos Ruth y Otto, y Brigitta y
Siegfried, que me han aconsejado y apoyado a lo largo de mi educación.
Gracias también a los padres de María, Martina y Johannes Helbig, por su
generosidad y su perspectiva fresca. A mis amigos, tanto aquí en México
– Domingo, María de la O, Oscar, Lina, Lariza, Gianluca, Daniele, Matteo,
Ramón, Alma, Mario, Fabián, y el equipo de básquet INDEREQ – como los
amigos de mi tierra: Martin, Matt, Bob, Mathias, Mel, Paul, Jo, y Nadja: les
debo demasiado. Gracias por todos los buenos momentos! Estoy especialmente agradecido a mi novia Maria, por su amor, aliento y su compañía en
esta aventura mexicana. Tú eres la luz de mi vida.
viii
ÍNDICE GENERAL
1
introducción
1.1 Marco geológico . . . . . . . . . . . . . . . . . . . . . . . . . . .
1.2 Motivación, objetivos y metodología . . . . . . . . . . . . . . .
1
1
5
2
geoquímica y geocronología de las unidades del carbonífero–pérmico
10
3
historia estructural del plutón totoltepec
4
eventos del paleozoico tardío hasta el mesozoico temprano en la periferia de pangea
58
5
resumen y conclusión
33
76
a métodos analíticos
a.1 Geocronología U-Pb . . . . . . . . . . . . . . . . . . . . . . . .
a.2 Geoquímica . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
a.3 Geocronología 40 Ar-39 Ar . . . . . . . . . . . . . . . . . . . . .
80
80
81
81
b
83
tablas geocronología u-pb
c tablas geoquímica
117
d tablas análisis de microsonda
138
e
tablas geocronología
40 ar/ 39 ar
bibliografía
146
148
ix
1
INTRODUCCIÓN
Esta tesis se concentra en el estudio del plutón Totoltepec de edad Carbonífero–Pérmico y sus rocas encajonantes (parte del Complejo Acatlán), con
énfasis en la geoquímica y el control estructural en el emplazamiento del
plutón. A pesar de que la geoquímica publicada (basada en 6 muestras: Malone et al., 2002) muestra una afinidad de arco, estos datos no fueron suficientes para distinguir entre magmas formados en una zona de subducción
y magmas contaminados por la corteza continental (Pearce y Peate, 1995;
Turner et al., 1996; Kuscu et al., 2010). Un muestreo más amplio y un conjunto más exhaustivo de los elementos y los isótopos analizados constituyen
la base para este estudio. Se obtuvieron datos geocronológicos adicionales
de U-Pb para determinar la edad y duración del evento de intrusión, complementándose con edades de 40 Ar/39 Ar para conocer también la historia
tectono-térmica. El estudio además incluye análisis geocronológicos y geoquímicos de las rocas sedimentarias contemporáneas a la intrusión para los
cuales no existían ningunos datos de este tipo. Aunque estudios anteriores
han sugerido que el emplazamiento del plutón Totoltepec fue sintectónico,
los controles estructurales no eran conocidos. La base de datos mejorada
que aporta este estudio permite el desarrollo de un modelo estructural para
el emplazamiento del plutón. Estas conclusiones se utilizan para documentar el desarrollo de un arco regional y para diferenciar entre los diferentes
modelos paleogeográficos para el Complejo Acatlán con respecto a Pangea
(Keppie et al., 2010; Vega-Granillo et al., 2009; Böhnel, 1999).
1.1
marco geológico
Con una extensión superficial que supera los 10,000 km2 , el Complejo
Acatlán de edad Ordovícico al Pérmico Medio constituye el basamento del
terreno Mixteca y el mayor afloramiento de rocas paleozoicas en México
(Ortega-Gutiérrez, 1978; Campa y Coney, 1983; Sedlock et al., 1993; Keppie,
2004). Las rocas expuestas en la región de Acatlán registran una historia
paleozoica tectonotermal muy compleja que refleja la apertura y el cierre
de una o más cuencas oceánicas y sus consiguientes interacciones continentales que culminaron en la amalgamación de Pangea (por ejemplo, Nance
et al., 2006). Estos eventos fueron acompañados por subducción durante el
Devónico hasta el Pérmico a lo largo del sur de México (Keppie et al., 2008).
El Complejo Acatlán está limitado al este por la falla de Caltepec, una zona de cizalla con dirección N–S y mecanismo dextral, que lo separa de los
gneises en facies de granulita de ∼1.0 Ga del Complejo Oaxaqueño (ElíasHerrera y Ortega-Gutiérrez, 2002). Al sur, está limitado por la falla Cenozoica La Venta-Chacalapa (Tolson, 2007; Solari et al., 2007), que lo yuxtapone
1
1.1 marco geológico
contra las rocas plutónicas y metamórficas de alto grado del Complejo Xolapa (Pérez-Gutiérrez et al., 2009). Hacia el oeste, sobreyace en forma de cabalgadura sobre carbonatos cretácicos de la plataforma Guerrero-Morelos,
que están expuestos entre el Complejo Acatlán y el terreno compuesto de
Guerrero (Centeno-García et al., 2008; Ramos-Arias y Keppie, 2011). Hacia
el norte, se encuentra cubierto discordantemente por rocas sedimentarias
de origen continental y marino de edad Pérmico Superior–Jurásico Medio
(Morán-Zenteno et al., 1993; Centeno-García et al., 2009), así como por rocas
volcánicas y volcaniclásticas del Mioceno Medio y Tardío de la Faja Volcánica Transmexicana (Ferrari et al., 1999).
El área de estudio se encuentra en la parte oriental del Complejo Acatlán,
a unos 30 km al este de Acatlán de Osorio (estado de Puebla). Está limitado
de forma aproximada por los pueblos Xayacatlán de Bravo al oeste, Santo
Domingo Tianguistengo al este y San José Chichihualtepec al sur. Las rocas estudiadas ocurren en el bloque tectónico Tonahuixtla (Morales-Gámez
et al., 2009), que está limitado en ambos lados por fallas normales-dextrales
de rumbo N–S. En base a los mapas geológicos publicados (Ortega-Gutiérrez,
1978; Malone et al., 2002; Keppie et al., 2004a), la estratigrafía del área de estudio está conformada por las siguientes unidades litotectónicas: el plutón
Totoltepec, la Formación Tecomate y la Formación Cosoltepec. A continuación se resumen los datos publicados sobre cada una de estas unidades y
se identifican las problemáticas científicas que se tratan de resolver en este
estudio.
El plutón Totoltepec, con una superficie de afloramiento de 15 × 5 km,
constituye la parte central del área de estudio. El cuerpo intrusivo fue nombrado por Fries et al. (1970) y primero cartografiado por Ortega-Gutiérrez
(1975), como parte de su trabajo pionero en el Complejo Acatlán. De acuerdo con Ortega-Gutiérrez (1978), el plutón está en contacto intrusivo con
rocas del Subgrupo Acateco y la Formación Cosoltepec (Grupo Petlalcingo,
Fig. 1). Por otro lado, Malone et al. (2002) y Keppie et al. (2004a) ubican el
plutón Totoltepec en el bloque cabalgante de una gran falla, estructuralmente sobreyaciendo las formaciones Tecomate y Cosoltepec. Hacia el norte, el
plutón está sobreyacido discordantemente por capas rojas deformadas, pero
sin metamorfismo, de edad inferida jurásica (Malone et al., 2002).
El plutón Totoltepec está conformado principalmente por diorita de hornblenda, trondhjemita y tonalita (Malone et al., 2002). Las fracciones de circón de una fase félsica han dado una edad concordante U-Pb TIMS de 287
± 2 Ma (Yañez et al., 1991), mientras que una fase máfica de la parte sur
del plutón dio una edad U-Pb TIMS de 289 ± 1 Ma (Keppie et al., 2004a).
Ortega-Gutiérrez (1975) ha documentado cuerpos de gneises máficos de estructura migmática y bandeada en el margen norte del plutón Totoltepec,
que Calderón-García (1956) sospecha pertenecen al basamento de la zona.
La edad de estas rocas máficas marginales y su significado geodinámico es
desconocido.
Una cantidad limitada de datos estructurales del plutón (Malone et al.,
2002; Morales-Gámez et al., 2009) sugieren la presencia de una foliación de
2
P
C
235
245
251
260
271
Formación
Patlanoaya
(Dev. tardío –
Pérmico
medio)
318
385
S
416
428
423
444
Plutón
La Noria
(337±34 Ma)
472
488
501
510
521
542
granitoides
Esperanza
(440±14 Ma)
Fm. Xayacatlán
Plutón
Totoltepec
Unidad
Salada ,
Cosoltepec
Exumación
de rocas de alta presión
(facies eclogita)
Orogenia Mixteca
(facies esquisto verde)
398
461
Grupo
Patlanoaya
& Fm.
Tecomate
Fm. Tecomate
Orogenia Acateca
(facies eclogita)
Fm. Cosoltepec
Fm. Chazumba
Mig. Magdalena
Ortega-Gutiérrez et al. (1999)
Grupo
Petlalcingo
D
_
Evento Orogénico
(facies esquisto verde)
299
359
O
Plutón
Totoltepec
(287±2 Ma)
Grupo Piaxtla
^
Huerta,
Amate, Las
Minas
magmatismo
bimodal
(480–440 Ma)
Nance et al. (2006)
Keppie et al. (2008)
Figura 1: Diagrama de relaciones espaciales y temporales que muestra la tectonoestratigrafía tradicional (izquierda) y revisada (derecha) del Complejo
Acatlán. Figura modificada de Ortega-Gutiérrez et al. (1999); Nance et al.
(2006); Keppie et al. (2008).
rumbo norte y buzamiento de alto ángulo, así como pliegues de dirección
N–S, por cual la foliación se encuentra plegada a nivel local. Además, Malone et al. (2002) sugieren que el emplazamiento del plutón puede haber sido
sintectónico con respecto a la deformación regional.
Datos geoquímicos de un estudio de reconocimiento de rocas del putón
Totoltepec reflejan una afinidad calco-alcalina (Malone et al., 2002). Isotópicamente, el plutón Totoltepec ha dado valores de Nd(t) más positivos y
edades modelo TDM más jóvenes (Yañez et al., 1991) en comparación a plutones contemporáneos en el sur de México, lo que indica que proviene de
una fuente de carácter más juvenil. La intrusión ha sido interpretada como
parte de un arco continental Pérmico–Triásico que se extiende a lo largo de
México centro-oriental (Torres et al., 1999; Malone et al., 2002; Keppie et al.,
2004a). Alternativamente, de acuerdo con su modelo paleogeográfico, VegaGranillo et al. (2009) consideran el plutón como un producto de la colisión
continental y una expresión local de la orogenia Ouachita-Alleganiana.
La Formación Tecomate, originalmente definida por Rodríguez-Torres
(1970), es una unidad clástica ligeramente metamorfoseada, pero intensamente deformada que consiste en alternancias de rocas psammiticas-pelíticas, mármoles y conglomerados de cantos rodados, así como rocas volcánicas que principalmente están formadas por flujos y tobas con escasas unidades félsicas (Ortega-Gutiérrez, 1993; Sánchez-Zavala et al., 2000). En su área
tipo, la Formación Tecomate ocurre en una zona de cizalla subvertical de
orientación N–S situado entre la ciudad de Acatlán de Osorio y el pueblo
de El Tecomate (Ortega-Gutiérrez, 1975), pero rocas correlacionables con la
3
Formación Tecomate también afloran localmente en los sectores norte y este (por ejemplo, Ortega-Gutiérrez et al., 1999), así como el sector oeste del
Complejo Acatlán (Talavera-Mendoza et al., 2005; Vega-Granillo et al., 2009).
Según mapas geológicos publicados de la zona de estudio, la Formación
Tecomate está en contacto con el plutón Totoltepec en su margen sur y este
(Ortega-Gutiérrez et al., 1999), así como en sus bordes suroriente y oeste
(Keppie et al., 2004a).
La edad de depositación de la Formación Tecomate es sujeto de controversia. Originalmente, se infirió como Devónica (Fig. 1) basada principalmente
en la presencia de equinodermos, crinoides, blastoideos y micromoluscos
de edad pre-Carbonífero obtenidos en esta unidad (Ortega-Gutiérrez, 1993)
y en la interpretación de que la formación está intruida por el granito La
Noria (Ortega-Gutiérrez et al., 1999), de los cuales datos U-Pb (circón) indicaban una edad Devónico Tardío. Sin embargo, más recientemente, la
fauna recuperada de tres horizontes diferentes de mármol ha permitido
precisar una edad pérmica temprana a media para la depositación de la
Formación Tecomate en el área tipo (Keppie et al., 2004b). Estas restricciones paleontológicos han sido corroboradas por edades U-Pb SHRIMP de
aproximadamente 320–264 Ma de circones separados de cantos de granito
en los metaconglomerados de la Formación Tecomate en la parte oriental
del Complejo Acatlán. Sin embargo, datos geocronológicos publicados de
la Formación Tecomate (Keppie et al., 2004b; Sánchez-Zavala et al., 2004;
Talavera-Mendoza et al., 2005) sugieren que la unidad, como se define actualmente, puede ser de diferentes edades en diferentes lugares.
La Formación Tecomate ha sido interpretada como un sedimento sinorogénico depositado posterior al emplazamiento de una capa cabalgante
(Ortega-Gutiérrez, 1993; Weber et al., 1997), una secuencia turbidítica relacionada a un arco volcánico depositado en la zona frontal de una colisión
de arco-continente (Sánchez-Zavala et al., 2000), un depósito de arco y de
extensión intracontinental (Talavera-Mendoza et al., 2005) y un sedimento
marino somero de ante-arco (Keppie et al., 2004b).
Basado en el traslape de las edades de depósito y similitudes faunísticas,
la Formación Tecomate se ha correlacionado con la Formación San Salvador
Patlanoaya de edad Devónico Superior a Pérmico Inferior en la parte norte
del Complejo Acatlán (Keppie et al., 2004b). Sin embargo, a diferencia de la
Formación Tecomate que ha sido deformada en forma penetrativa y afectada por metamorfismo en facies del esquisto verde, la Formación Patlanoaya
no está metamorfoseada y casi no ha sido deformada.
Mediciones de la forma de clastos en metaconglomerados de la Formación Tecomate en el área de estudio cerca de San José Chichihualtepec han
dado esferoides alargados, con dimensiones típicos de la deformación transtensional (Morales-Gámez et al., 2009). Una edad 40 Ar/39 Ar de 263 ± 3 Ma
para una filita sericítica de la Formación Tecomate adyacente a la zona de
estudio ((Morales-Gámez et al., 2009) define el límite de edad de esta deformación. Adicionalmente, se ha documentado cizallamiento lateral N–S
entre aproximadamente 307 y 269 Ma a lo largo de la falla Caltepec (Elías-
4
1.2 motivación, objetivos y metodología
Herrera y Ortega-Gutiérrez, 2002; Elías-Herrera et al., 2005). El significado
del mecanismo y los límites temporales de la deformación con respecto a la
configuración paleogeográfica regional y su papel en el emplazamiento del
plutón Totoltepec permanecen inexplorados.
Se ha reportado que la Formación Cosoltepec aflora en la parte sur de
la zona de estudio, donde está en contacto con el plutón Totoltepec en sus
márgenes sur y oeste (Ortega-Gutiérrez, 1978; Ortega-Gutiérrez et al., 1999;
Malone et al., 2002). En el mapa geológico de Keppie et al. (2004a), las rocas
de la Formación Cosoltepec sólo afloran en una zona estrecha a lo largo
del límite suroeste del plutón Totoltepec. La Formación Cosoltepec está definida como una secuencia monótona de metapelitas y metapsamitas con
escasas intercalaciones de anfibolita. Originalmente la unidad fue incluida
en el Grupo Petlalcingo de edad Cámbrico–Ordovícico (Ortega-Gutiérrez,
1978), pero trabajos geocronológicos recientes han identificado grupos de
circones detríticos más jóvenes de edad Ordovícico (∼455 Ma: Keppie et al.,
2004a, 2006), Devónico-Carbonífero (∼410 y/o ∼374 Ma: Talavera-Mendoza
et al., 2005), o de edad Carbonífero (∼352 Ma: Morales-Gámez et al., 2008)
en las unidades asignadas originalmente a la Formación Cosoltepec; esto
indica que está compuesta por diferentes unidades. El ambiente tectónico
para la depositación de las rocas de la Formación Cosoltepec sigue siendo
parte de la discusión en curso, ya que la unidad ha sido interpretada como un prisma de acreción (Ortega-Gutiérrez et al., 1999), una secuencia del
margen pasivo (Talavera-Mendoza et al., 2005; Vega-Granillo et al., 2007) o
un depósito de la eminencia continental (Keppie et al., 2006).
1.2
motivación, objetivos y metodología
Basado en una serie de estudios de reconocimiento del área (por ejemplo, Yañez et al., 1991; Malone et al., 2002; Keppie et al., 2004a,b), el plutón
Totoltepec y la Formación Tecomate son propuestos como pertenecientes a
un arco magmático continental del Pérmico–Triásico que se extiende desde
el suroeste de los Estados Unidos y continua a lo largo de México centrooriental (Centeno-García y Silva-Romo, 1997; Torres et al., 1999; Dickinson
y Lawton, 2001). Sin embargo, la existencia de este arco se basa en (i) una
cantidad limitada de datos geocronológicos, la mayoría de los cuales se han
obtenido utilizando métodos isotópicos K-Ar y Rb-Sr (por ejemplo, Torres
et al., 1999; Schaaf et al., 2002; Yañez et al., 1991) que son conocidos por ser
indicadores menos confiables para establecer la edad de cristalización de un
plutón en comparación a la geocronología U-Pb de circones (por ejemplo,
Steiner y Walker, 1996), y (ii) escasos datos geoquímicos de rocas ígneas del
Paleozoico tardío en México (Torres et al., 1999; Solari et al., 2001; Malone
et al., 2002; Rosales-Lagarde et al., 2005; Arvizu et al., 2009). Por otra parte,
una firma geoquímica de arco en las rocas ígneas de composición félsica
e intermedia suele interpretarse como una evidencia directa de magmatismo de arco contemporáneo. Sin embargo, modelos para la generación de
magma intermedio y silícico incluyen tanto la diferenciación de magmas
5
máficos derivados del manto por cristalización fraccionada dentro de la
corteza o el manto superior (por ejemplo, Gill, 1981), como la fusión parcial
de rocas de la corteza pre-existente (por ejemplo, Thompson, 1982). Por lo
tanto, una firma geoquímica de arco en rocas ígneas de composición félsica o intermedia puede ser adquirido como resultado de la subducción de
litosfera oceánica (por ejemplo, Pearce y Peate, 1995), o por la fusión de
la corteza continental que ha sido generada por procesos de subducción
(por ejemplo, Turner et al., 1996; Kuscu et al., 2010). La composición isotópica y/o la abundancia de xenolitos de granulita en las rocas ígneas que se
utilizaron para definir el arco magmático continental del Pérmico–Triásico
indican que están significativamente contaminados por la corteza continental. El terreno Oaxaquia, que incluye rocas de aproximadamente 1.0 Ga del
núcleo cristalino de México, registra un episodio de magmatismo de arco
entre aproximadamente 1300 y 1200 Ma (Keppie y Ortega-Gutiérrez, 2010).
Por lo tanto, las abundancias de los elementos exhibidos por las rocas de
arco principalmente félsicas, derivados de la corteza o contaminados que
intruyen el basamiento de tipo Oaxaquia, puede reflejar una herencia en
lugar de una firma de arco original. Antes de poder utilizar estas rocas
para reconstruir la evolución de un arco magmático, el origen de la firma
geoquímica con respecto a la generación de magmas félsicos tiene que ser
evaluado críticamente. Se necesitan más datos y una evaluación rigurosa
de éstos para demostrar de manera incuestionable la existencia de un arco
regional del Paleozoico tardío. En este estudio, datos geocronológicos, geoquímicos y estructurales del plutón Totoltepec son combinados con datos
geoquímicos y geocronológicos de rocas volcaniclásticas contemporáneas
de la Formación Tecomate, para proporcionar un modelo de los procesos
relacionados con la subducción en diferentes niveles de la corteza y además refinar las características temporales y espaciales, así que la evolución
del arco propuesto.
En cinturones orogénicos el plutonismo granitoide se presenta con frecuencia asociado espacial y temporalmente con sitios de deformación activa (Hutton, 1988), donde el ascenso y el emplazamiento de magma pueden
ser controlados por zonas de cizallamiento de niveles corticales profundos
(Brown y Solar, 1998). En un estudio de reconocimiento, Malone et al. (2002)
observaron que los diques que cortan la foliación de forma oblicua en el plutón Totoltepec contienen una foliación interna paralela a sus márgenes del
dique, lo que sugiere un posible emplazamiento sintectónico con respecto a la deformación regional. Sin embargo, no existen datos estructurales
definitivos que establezcan los plazos de la deformación en relación al estado de cristalización del plutón (siguiendo los criterios de, por ejemplo,
Blumenfeld y Bouchez, 1988; Paterson et al., 1989, 1991; Miller y Paterson,
1994) para sustanciar la naturaleza sin-cinemática de intrusión. Mostrar que
el emplazamiento del plutón fue acompañado por deformación regional es
de suma importancia, ya que los plutones sintectónicos bien datados se
pueden utilizar para evaluar la temporalidad, el mecanismo y la historia
térmica de la deformación regional (por ejemplo, Ingram y Hutton, 1994;
6
Tribe y D’Lemos, 1996). Teniendo en cuenta los trabajos anteriores, que han
relacionado el plutón Totoltepec con un arco magmático regional, un plutón
emplazado sintectónicamente marcaría un lugar excepcionalmente adecuado para investigar la cinemática y el desarollo geodinámico de un sistema
de falla en un arco continental antiguo y explorar la relación entre el magmatismo granitoide y la deformación en un margen de placa convergente.
Este estudio demuestra que el emplazamiento fue contemporáneo con la deformación, proporciona límites en cuanto a profundidad de emplazamiento,
tasa de exhumación e historia de enfriamiento del plutón, empleando una
combinación de geocronología U-Pb y 40 Ar/39 Ar, el análisis de meso y microfábrica y de termobarometría de aluminio en hornblenda. Además, el
estudio identifica el desarrollo de las fábricas, la secuencia temporal y los
mecanismos de emplazamiento de las diversas fases intrusivas. Por otra
parte, se desarrolla un modelo que pretende explicar el emplazamiento del
plutón en el contexto de fallamiento regional de orientación N–S y mecanismo transcurrente-dextral. Estos datos ayudan a entender la cinemática
del sistema de fallas que permitió el emplazamiento y la exhumación del
plutón como un medio para reconstruir la evolución geodinámica del arco
magmático del Paleozoico tardío.
Existen dos modelos en competencia concernientes a la posición paleogeográfica del terreno Mixteco en relación a la configuración de Pangea en
el Paleozoico. Keppie et al. (2010) y Weber et al. (2007) ubican el terreno Mixteca en el margen activo occidental de Pangea, mientras que Vega-Granillo
et al. (2009) consideran que el terreno se ubicó en la zona de colisión entre Gondwana y Laurentia. Un tercer modelo, que se basa en un modelo
alternativo de Pangea (Pangea-B, Irving, 1977; Morel y Irving, 1981) invocando un mega-sistema de cizallamiento dextral, coloca el terreno Mixteca
frente al nordeste de Canadá en el Jurásico (Böhnel, 1999). Por lo tanto,
la ubicación del terreno Mixteca en el sur de México en las reconstrucciones paleogeográficas del Paleozoico tardío tiene implicaciones profundas
para las hipótesis Pangea-A y -B. En este estudio, se evalúan los diferentes escenarios; la evaluación se basa en determinar la fuente de magma
y el mecanismo de emplazamiento del plutón Totoltepec, así como el ambiente tectónico y la procedencia de la Formación Tecomate. A su vez, esto permite evaluar el significado geodinámico de estas rocas en relación
con la amalgamación y la desintegración de Pangea. Dependiendo de si la
ubicación paleogeográfica del terreno Mixteca en el Paleozoico tardío era
periférica o interna con respecto a Pangea, el magmatismo y los procesos
de formación de cuenca caracterizados por el plutón Totoltepec y la Formación Tecomate representan eventos relacionados a la subducción en un
orógeno periférico del tipo andino, o eventos colisionales parecidos a las de
la orogenia Ouachita-Alleganiana en el sur de los Apalaches. Estos procesos
del Paleozoico tardío en cualquier de los dos ambientes tectónicos posibles
son pertinentes a un proceso importante de escala global que involucra la
transferencia de las zonas de subducción desde el interior de Pangea a la
periferia (por ejemplo, Murphy y Nance, 2008; Murphy et al., 2009).
7
En la primera sección de este trabajo se presentan los datos geológicos de
campo, petrografía, geocronología U-Pb de circones y geoquímica de elementos mayores y trazas, así como geoquímica isotópica de Sm-Nd para
el plutón Totoltepec y la Formación Tecomate de la zona de estudio. Las
descripciones detalladas de las metodologías están incluidas en el Apéndice A.1. Las edades de cristalización de las fases plutónicas y las edades
detríticas de las rocas metasedimentarias fueron obtenidas por medio de la
ablación láser (LA-ICP-MS) en el Laboratorio de Estudios Isotópicos (LEI),
Centro de Geociencias, UNAM. Los granos de circón fueron separados utilizando diferentes protocolos analíticos con el fin de maximizar la pureza del
concentrado obtenido, así como minimizar cualquier sesgo. Se realizaron
observaciones por catodoluminiscencia (CL) antes de los análisis LA-ICPMS para ayudar a la selección de puntos y para aumentar la interpretabilidad geológica de los resultados. Los datos de edad son utilizados para
establecer la secuencia de intrusión del plutón Totoltepec, la edad máxima
de sedimentación y la procedencia de la Formación Tecomate en el área de
estudio. Los datos geoquímicos (véase el Apéndice A.2 para detalles metodológicos), obtenidos del Regional Geochemical Centre de Saint Mary’s
University en Nueva Escocia, Canadá, se utilizan para evaluar el ambiente
tectónico del plutón Totoltepec y la Formación Tecomate. Datos isotópicos
de Sm-Nd, adquiridos del Atlantic Universities Regional Isotopic Facility
(AURIF), Memorial University en Terranova, Canadá, se emplean como trazador tectónico para investigar la fuente de magma del plutón Totoltepec y
para proporcionar información sobre la procedencia de las rocas de la Formación Tecomate; éstos complementan los datos geocronológicos. También
se incluye una revisión de los datos geocronológicos, geoquímicos e isotópicos de los sistemas magmáticos aproximadamente coetáneos en México y
Guatemala así como propios datos geoquímicos e isotópicos de los plutones
Cozahuico y La Carbonera en el Complejo Oaxaqueño.
La segunda sección de la tesis contiene datos meso- y micro-estructurales,
petrográficos, de microsonda, termobarométricos y geocronológicos del plutón Totoltepec; éstos se utilizan para investigar la historia de emplazamiento
del plutón y su significado en el desarrollo geodinámico del arco continental del Paleozoico tardío en el sur de México. Se llevó a cabo un extenso
trabajo de campo para documentar las relaciones de contacto internos y
externos al plutón, recabar datos estructurales, así como muestrear para
secciones delgadas, análisis de microsonda y análisis geocronológicos. Las
observaciones petrográficas de láminas delgadas y los análisis de microsonda se utilizan para examinar la asociación de fases y para determinar la
composición de algunos minerales. La historia de la deformación del plutón está reconstruida sobre la base de microestructuras distintivas que se
desarrollan por diferentes mecanismos de recristalización dinámica. Con el
fin de obtener una estimación de la profundidad del emplazamiento y la
tasa de exhumación, se emplea una combinación de termobarometría Alen-hornblenda y dataciones por el método 40 Ar/39 Ar. Los datos químicos
de plagioclasa y hornblenda coexistente fueron obtenidos mediante micro-
8
sonda electrónica y espectrometría de dispersión por longitud de onda en
el Laboratorio Universitario de Petrología (LUP) del Instituto de Geofísica
(UNAM) en la Ciudad de México. Los fechamientos de moscovita mediante 40 Ar/39 Ar se llevaron a cabo por un procedimiento de calentamiento
en pasos con láser en el Geochronology Research Laboratory de Queen’s
University en Kingston, Canadá (véase el Apéndice A.3 para las especificaciones técnicas y detalles del método analítico). En conjunto, estos datos se
utilizan para explicar la intrusión, deformación y exhumación del plutón
en el contexto del marco estructural regional.
La tercera sección está constituida por una guía de una excursión geológica, publicada como parte del Programa Internacional de Correlación
Geológica Proyecto 597 (IGCP—amalgamación y ruptura de Pangea) y la
108a Reunión Anual de la Sección Cordillerana del GSA en Querétaro, México (28 a 31 marzo 2012). La guía da una visión general de los eventos del
Pensilvánico–Jurásico en la periferia de Pangea. El capítulo correspondiente
a la zona de estudio describe las relaciones de campo en una serie de afloramientos considerados principales y resume datos publicados. Además,
contiene datos nuevos de geocronología U-Pb y 40 Ar/39 Ar, geoquímica y
geoquímica isotópica Sm-Nd.
9
GEOQUÍMICA Y GEOCRONOLOGÍA DE LAS UNIDADES
DEL CARBONÍFERO–PÉRMICO
Artículo: Kirsch, M., Keppie, J.D., Murphy, J.B., y Solari, L.A., 2012, Permian–Carboniferous arc magmatism and basin evolution along the western
margin of Pangea: geochemical and geochronological evidence from the
eastern Acatlán Complex, southern Mexico: Geological Society of America
Bulletin, en prensa, doi: 10.1130/B30649.1.
Contribuciones individuales de los autores:
Moritz Kirsch: concepción y diseño del estudio; trabajo de campo el
cual incluye mapeo, selección de puntos de muestreo y toma de muestras para análisis de geoquímica y geocronología U-Pb; adquisición de
los datos LA-ICP-MS, incluyendo la separación de circones y catodoluminiscencia; revisión de literatura; análisis e interpretación de datos;
redacción del artículo.
J. Duncan Keppie: contribución a la concepción y el diseño; supervisión de las actividades de campo; participación en la interpretación de
los datos y en la revisión del artículo remitido; adquisición de fondos.
J. Brendan Murphy: contribución a la concepción y el diseño; supervisión de las actividades de campo; participación en la interpretación de
Luigi A. Solari: participación en la interpretación de datos y en la revisión del artículo remitido; responsable de las instalaciones de análisis
LA-ICP-MS.
10
2
Downloaded from gsabulletin.gsapubs.org on September 13, 2012
Permian–Carboniferous arc magmatism and basin evolution along
the western margin of Pangea: Geochemical and geochronological
evidence from the eastern Acatlán Complex, southern Mexico
Moritz Kirsch1,†, J. Duncan Keppie2, J. Brendan Murphy3, and Luigi A. Solari1
1
Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, 76230 Querétaro, QRO, Mexico
Departamento de Geología Regional, Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México D.F., Mexico
3
Department of Earth Sciences, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
2
ABSTRACT
In the Acatlán Complex of southern Mexico, a late Paleozoic assemblage, consisting of
a gabbro-diorite-tonalite-trondhjemite suite
(Totoltepec pluton) and clastic-calcareous
metasedimentary rocks (Tecomate Formation), postdates collisional orogeny that resulted in the amalgamation of Pangea. This
region offers a rare opportunity to examine
assemblages developed at different crustal
levels along the periphery of Pangea at the
critical stage between amalgamation and
breakup. The Totoltepec pluton consists of
minor mafic-ultramafic rocks (306 ± 2 Ma;
concordant U-Pb zircon analysis) that are
marginal to the main mafic-felsic intrusion
(289 ± 2 Ma). Geochemistry of the marginal
rocks indicates an arc tholeiitic to calc-alkaline character with high large ion lithophile elements (LILEs)/high field strength
elements (HFSEs), flat rare earth element
(REE) patterns, and initial εNd values of
+1.3 to +3.3. The younger Totoltepec phase
exhibits a calc-alkaline trace-element geochemistry with flat to moderately fractionated light (L) REE–enriched patterns and
initial εNd values of –0.8 to +2.6, which are
also consistent with an arc environment. The
Sm-Nd isotopic signature is more primitive
compared to contemporaneous arc-related
igneous rocks in southern Mexico, suggesting the pluton was emplaced in a less mature, outboard part of the arc, and/or along
a fault conduit. The Tecomate Formation, as
currently defined, is a composite of lithologically similar strata deposited in several faultbounded basins ranging from Carboniferous
to Early Permian in age. To the south of the
†
E-mails: [email protected]; moritz
[email protected]
Totoltepec pluton, the depositional age of the
Tecomate Formation is tightly constrained in
one section to ca. 300 Ma, but in another section, it is between ca. 288 and ca. 263 Ma. The
Tecomate Formation rocks are interpreted
to have been derived from a late Paleozoic
arc based on (1) arc-related geochemistry,
(2) εNd (t) values ranging from –5.6 to +0.3 (t =
288 Ma) that overlap those of the Totoltepec
pluton, and (3) detrital zircons with predominantly Carboniferous–Permian ages. The
Totoltepec and Tecomate units in the study
area form part of a continental arc extending
from Guatemala to California, which necessitates subduction of the paleo-Pacific oceanic lithosphere beneath the western margin
of a Pangea-A configuration.
INTRODUCTION
Although it is accepted that Pangea had
largely been assembled by the Carboniferous–
Permian, two competing models have been
proposed for the late Paleozoic configuration of
the supercontinent: Pangea-A, essentially the
“Wegenerian” fit (Bullard et al., 1965; Smith
and Hallam, 1970), and Pangea-B (Irving, 1977;
Morel and Irving, 1981; Muttoni et al., 2003),
which is based on the paleomagnetic data in
which Gondwana is positioned ~3000 km
farther east relative to Laurasia. In paleogeographic reconstructions of Pangea-A, southern
Mexico occupies a position similar to its present
location relative to North America (Figs. 1A and
1B; e.g., Fang et al., 1989; Alva-Valdivia et al.,
2002), whereas in reconstructions of Pangea-B,
southern Mexico is placed off eastern Canada
during the Jurassic (Fig. 1C; Böhnel, 1999).
There are also variants of the Pangea-A reconstruction, in which southern Mexico is either
peripheral (Keppie, 2004; Keppie et al., 2008a,
2010; Fig. 1A) or internal to Pangea, between
the Maya terrane and the southern United States
(Talavera-Mendoza et al., 2005; Vega-Granillo
et al., 2007, 2009; Fig. 1B).
Based on reconnaissance studies (e.g., Keppie
et al., 2004a), the Totoltepec pluton and the
Tecomate Formation in the eastern Acatlán
Complex (Mixteca terrane) of southern Mexico
are inferred to be part of a late Paleozoic continental arc assemblage that extended from
the southern United States through Mexico to the
northern Andes (Torres et al., 1999; Dickinson
and Lawton, 2001). Alternatively, in accordance
with their hypothesized within-Pangea location,
Vega-Granillo et al. (2009) attributed late Paleozoic tectonothermal events in southern Mexico
(including the eastern Acatlán Complex) to be
related to continental collision (Alleghanian
orogeny). In order to test the validity of these
contrasting models, we investigated the tectonic
setting of the Totoltepec pluton and Tecomate
Formation using a combination of new geochemical, isotopic, and geochronological data.
Examining magmatic systems in conjunction
with sedimentary rocks enables the expression
of tectonic events at different crustal levels to be
documented.
Almost all of the crystallization ages of plutons used by Torres et al. (1999) to constrain
the age of the hypothesized magmatic arc
were obtained using K-Ar or Rb-Sr isotopic
methods, which are known to be susceptible to
postcrystallization processes and hence may be
less precise than U-Pb zircon geochronology
in obtaining ages of magmatic crystallization.
The central phase in the Totoltepec pluton has
been investigated by reconnaissance U-Pb geochronology (Yañez et al., 1991; Keppie et al.,
2004a). However, mafic igneous rocks at the
margin of the Totoltepec pluton have not been
dated, so the age range of the pluton is not constrained, and its regional significance is unclear.
Although the existence of a Permian–Triassic
GSA Bulletin; September/October 2012; v. 124; no. 9/10; p. 1607–1628; doi:10.1130/B30649.1; 15 figures; 1 table; Data Repository item 2012220.
For permission to copy, contact [email protected]
© 2012 Geological Society of America
1607
Kirsch et al.
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Figure 1. Paleogeographic reconstructions showing the location of the Mixteca terrane (Mx) in different configurations: (A) at the western
margin of Pangea-A (modified after Weber et al., 2007), (B) within Pangea-A (modified after Vega-Granillo et al., 2009), or (C) off eastern
Canada in the Jurassic (Pangea-B; modified after Böhnel, 1999). Oax—Oaxaquia terrane; Coa—Coahuila terrane; CM—Chiapas Massif;
CA—Colombian Andes.
arc in Mexico has been proposed (e.g., Torres
et al., 1999; Dickinson and Lawton, 2001;
Centeno-García, 2005), geochemical data of late
Paleozoic igneous rocks that would test this proposal are scarce (Torres et al., 1999; Solari et al.,
2001; Malone et al., 2002; Rosales-Lagarde et al.,
2005; Arvizu et al., 2009). Thus, neither the
age nor the geochemistry of the magmatism,
which are both crucial in assessing its potential
geodynamic connection to the evolution of Pangea, is precisely constrained. We present U-Pb
geochronology coupled with geochemical and
Sm-Nd isotopic data to refine the age range of
the hypothesized late Paleozoic arc in southern
Mexico and to assess its geodynamic significance relative to the amalgamation and breakup
of Pangea.
Sedimentary sequences containing detritus
from an orogenic source provide complementary data that can be used to constrain the role
of basin formation as well as uplift and exhumation of the crust during orogenesis. Conglomerates in the Tecomate Formation in the study area
contain granitic pebbles (Keppie et al., 2004b),
suggesting a potential linkage between magmatism and basin evolution. However, based on the
available data, it is unclear whether the Tecomate Formation, which has been mapped on the
basis of lithologic comparison, is the same age
in different locations. In this paper, we investigate this possibility by providing U-Pb laserablation–inductively coupled plasma–mass
spectrometry (LA-ICP-MS) age data of single
detrital zircon grains to help constrain the depositional age of the Tecomate Formation in the
study area as well as enable a comparison with
the equivalent data from the type area in the central Acatlán Complex. In addition, we combine
these data with petrographic, geochemical, and
Sm-Nd isotopic evidence to assess the prov-
1608
enance and tectonic setting of these metasedimentary rocks.
Taken together, the data from the Totoltepec
pluton and the Tecomate Formation constrain
processes operating at different crustal levels
at a critical time in the evolution of Pangea.
These data also bear on the Pangea-A versus
Pangea-B controversy and on the location of
southern Mexico in reconstructions of Pangea.
If indeed southern Mexico was in a peripheral position with respect to Pangea in the late
Paleozoic (Pangea-A configuration), then this
region offers a rare opportunity to examine
the subduction-related magmatic and basinforming events after continental collision. If, on
the other hand, the magmatism and basin formation reflect collisional orogenesis (Pangea B
configuration), this region provides a record of
these processes that can be compared with the
Alleghanian orogeny in the Southern Appalachians. Our results indicate that the Totoltepec
pluton and Tecomate Formation were both
situated on the outboard part of a regionally
extensive Pennsylvanian–Permian continental
arc, consistent with subduction of paleo-Pacific
oceanic lithosphere beneath the western margin
of North America in a Pangea-A configuration.
GEOLOGICAL SETTING
The Acatlán Complex in southern Mexico is
tectonically bounded to the east by the Permian
Caltepec fault zone, which separates it from
the ca. 1 Ga Oaxacan Complex (Elías-Herrera
and Ortega-Gutiérrez, 2002), and to the south
by the Cenozoic La Venta and Chacalapa faults
(Tolson, 2007; Solari et al., 2007), juxtaposing
it against the Xolapa Complex (Fig. 2). To the
west, the Acatlán Complex is thrust over Cretaceous platformal carbonates, located between
the exposed Acatlán Complex and the emplaced
Guerrero terrane (Centeno-García et al., 2008;
Ramos-Arias and Keppie, 2011). To the north,
the complex is unconformably overlain by
Mesozoic rocks and the Cenozoic Trans-Mexican volcanic belt (Ferrari et al., 1999).
The geological history of the Acatlán Complex was recently summarized by Keppie et al.
(2008a) and Vega-Granillo et al. (2009) and is
not repeated here. Despite differences in the
interpretation of this history, all authors agree
that the late Paleozoic events involved subduction-related tectonothermal events; however,
the polarity of subduction is debated, either
eastward beneath Pangea (Keppie et al., 2008a)
or northward beneath Laurentia (Vega-Granillo
et al., 2009).
The Totoltepec pluton and the Tecomate Formation both occur within the Tonahuixtla fault
block (Morales-Gámez et al., 2009), which is
bounded in the west by the N-S–trending dextral San Jerónimo fault (Fig. 3; Morales-Gámez
et al., 2008), where the Tecomate Formation
is tectonically juxtaposed against the Carboniferous Salada unit along N-striking, dextralnormal faults and above N-dipping shear zones
(Morales-Gámez et al., 2008). In the east, the
Totoltepec pluton and Tecomate Formation are
delimited by the Tianguistengo normal fault
(Fig. 3; Servicio Geológico Mexicano, 2001).
Along its southern margin, the Totoltepec pluton is thrust over metasedimentary rocks of the
Tecomate Formation (Malone et al., 2002). The
southern limit of the Tecomate Formation is not
exposed in the study area, but the unit is inferred
to structurally overlie rocks of the Cosoltepec
Formation further south (Malone et al., 2002).
The Cosoltepec Formation was originally
thought to have been deposited in the Cambrian–Ordovician (Ortega-Gutiérrez, 1978), but
recent geochronological data indicate that it is
a composite of both Cambrian–Ordovician and
Geological Society of America Bulletin, September/October 2012
GUERRERO
MORELOS
PLATFORM
tl a
lu
th
ru
st
ru
st
tf
X
lt
Xo
af
au
A X
A Q U I A
Puerto
Escondido
la p
O
A
sa f
a ul
t
ld
ar
P
Coahuila
Central
B
Z
110°W
ca
C al te p e c f a u l t
C
ha
U
mo
l
M
Co
lex
Ca
ific
Oc
Juarez
M
Oaxaquia
(Middle
America)
Xo
Cz
Pac
mp
Cu
tf/ctf
pa Tt
tz Tz
U
LF
Laramide
front
O
F
ea
Ch
100°W
O
Yucatán
platform
IC
as
si
f
90°W
Ac
Maya
(Middle
America)
m
M
EX
500 km
n
Igneous rocks
dated by U-Pb methods
(Meta-)sedimentary rocks
Igneous rocks dated by K-Ar and
Rb-Sr methods
Xol
tu
As gu/dm
su
ita
apa
hon–Oua c
at
h
tz—Tuzancoa
pa—Patlanoaya
tf/ctf—Tecomate Type/
Chichihualtepec Tecomate
s
Figure 2. (A) Tectonic map showing the main crustal blocks and geologic provinces of Mexico and northern Central America. Location and extent of the Oaxaquia and Mixteca terranes are after Keppie (2004) and Dowe et al. (2005). Guerrero composite terrane is after Keppie (2004) and Centeno-García et al. (2008). Trans-Mexican volcanic belt
is after Ferrari (2004). (B) Subset of A showing the location of the study area (box) with respect to the principal geologic features of southern Mexico (modified from Keppie
et al., 2008a). Squares, circles, and triangles indicate the location of Carboniferous–Permian arc-related igneous and sedimentary rocks in Mexico (see text for references).
LE
J
ta H
er
A
rra
Pa
E
Paleozoic
Acatlán Complex
Mesoproterozoic
Oaxacan Complex
MP
Vis
Y
Oaxaca
lt
A C
O
Cu
fau
AP
A
rf
Tarahumara
R
XOL
Ca
aca
pa
Acapulco
Cz
Tehuacán
M
Oa x
ia
L a Ve n t a f a u l t
Tt
ctf
Fig. 3
Tahue
Cortez
North American
craton
SM
M
Sedimentary rocks
rf—Rara / Sierra del
Cuervo
ld—Las Delicias
gu/dm—Guacamaya /
Del Monte
re
M—Mixtequita
Ch—Chiapas Massif
Ac—Altos Cuchumatanes
ra Madre
M I X T E C A
th
Acatlán
de Osorio
pa
Puebla
Oaxaquia (Middle America)
Guerrero composite terrane
Trans-Mexican
Volcanic Belt
Mixteca
ja
pa
Caborca
Tt—Totoltepec
Ca—La Carbonera
Cu—Cuananá
Xo—Xolapa (Pto
Escond.)
Ba
Ch
10°N
120°W
20°N
A
t
n
er
Pa
30°N
es
s
Te
íno
ca yal
Viz Cho
W
to
l ol o ap
an
S
N&
Sie r
Carb.
Perm.
Al
i
is
G
Igneous rocks dated
by U-Pb
P—La Pezuña
As—El Aserradero
Tz—Tuzancoa
Cz—Cozahuico
Permian–Carboniferous arc magmatism and basin evolution along the western margin of Pangea
1609
69
81
81
71
69
86
63
25
26
70
52
86
88
28
59
TT-59
84
U/Pb
63 sampling points
TT-90
geochemistry
pts.
78
TT-89 sampling
85
TT-60
TT-57
78
42
50
89
86
TT-74
Cities
Highways
Roads
Rivers
16
TT-52
TT-20
67
88
44
54
37
55
TT-5B 57
TT-6
TT-83A
TT-5A
TT-7B
TT-7A
TT-51
86
77
75
74
TT-8B
TT-8A
77
64
52
63
72
67
TT-22
37
72
34
76
TT-50
86
83
59
80
TT-82
40
50
TT-40B
TT-39
TT-34A,B
TT-35
TT-36
TT-37A,B
39
TT-26B
TT-26A
68
4
TT-32 TT-33
33
TT-43
TT-8141
TT-27
TT-28
TT-38A,B
TT-25
Cretaceous
Jurassic
50
61
Chichihualtepec
90
Tecomate Fm.
Unnamed Unit
62
Salada Unit
27
TT-24
89
TT-49
63
48
45
84
68
Santo Domingo Tianguistengo
32
97°48′0″W
55
Lineation
Foliation
25
Granodiorite,
Chichihualtepec monzogranite
Contact
C. inferred
Trondhjemite
Strike-slip fault
Diorite,
tonalite,
felsic
and
mafic dikes
Normal fault
Hornblende gabbro, hornblendite
Thrust fault
75
80
74
29 55
68
5
TT-73
TT-18
9
Totoltepec de Guerrero
40
86
TT-72
TT-72
73
2
km
TT-76ATT-11
78
55
TT-77
54
TT-76b
81
TT-53 TT-78
60
TT-56
TT-54
TT-12
TT-13A
77TT-13B
54
20Domingo Tonahuixtla
Santo
36
TT-55
TT-79
14
76
56
TT-61A
TT-61B
TT-62 90
82
TT-84
TT-63A
TT-63B
TT-70
76
TT-615 TT-66
71
TT-69
89
TT-68
TT-67
TT-612
63
TT-85
TT-65
78
65
70
37
1
Scale 1:65,000
0.5
97°50′0″W
Figure 3. Geological map of the Totoltepec area showing sample locations for geochronological and geochemical analyses.
41
TT-15
TT-16
0
ult
nza fa
79
Mata
65
72
TT-14
68
Tonahuixtla fault block
54
57
San Jerónimo de Xayacatlán43
54
45
TT-486A
TT-486B
97°52′0″W
lt
18°16′0″N
18°14′0″N
fau
18°12′0″N
1610
ngu
go
o fault
Tia
n
iste
San Jerónim
97°54′0″W
Kirsch et al.
Totoltepec pluton
Devonian–Carboniferous units (Talavera-Mendoza et al., 2005; Keppie et al., 2006, 2008b;
Morales-Gámez et al., 2008; Ortega-Obregón
et al., 2009). To the northeast, an unnamed
amphibolites-facies unit (consisting of garnet
schist and quartzite with rare amphibolite dikes)
is in tectonic contact with the Totoltepec pluton
and the Tecomate Formation (Fig. 3). An unconformity, locally modified by normal faulting,
marks the northern contact between the pluton
and overlying red beds of inferred Jurassic age
(Malone et al., 2002).
The Totoltepec pluton is compositionally
diverse, ranging from hornblendite and hornblende gabbro through diorite to tonalite,
trondhjemite, granodiorite, monzogranite, and
quartz-rich granitoid. The petrography of these
rocks is described in detail in Kirsch et al.
(2012). Plagioclase-rich cumulates are found locally in the central part of the pluton. The hornblendite and hornblende gabbro occur only in
three 0.2–0.6 km2 lens-shaped bodies along the
northeastern margin of the pluton that coincide
with relatively high-amplitude magnetic anomalies (Servicio Geológico Mexicano, 2004a,
2004b). Although the exposed contacts between
the main and marginal phases are faults, the marginal bodies are cut by trondhjemitic dikes identical to those in the main phase, implying that the
faults have limited displacement. Only the trondhjemite and diorite were dated, and they yielded
ages of 287 ± 2 Ma and 289 ± 1 Ma, respectively
(U-Pb thermal ionization mass spectrometry
[TIMS] zircon ages; Yañez et al., 1991; Keppie
et al., 2004a). Within the pluton, a locally developed, subvertical fabric is defined by flattened
quartz and feldspar grains as well as by aligned
hornblende. Al-in-hornblende thermobarometric
data from the main phase (Kirsch et al., 2012)
indicate that the pluton was emplaced into midcrustal levels (~20 km).
The Tecomate Formation adjacent to the
Totoltepec pluton consists of greenschist-facies
metapelite, feldspar-bearing metapsammite
with local intercalations of metaconglomerate, unfossiliferous marble horizons, and rare
very fine-grained, green, tuffaceous layers. The
metapsammites are made up of quartz, plagioclase, and K-feldspar, phyllosilicates (white
mica, biotite partially altered to chlorite), and
opaque minerals, as well as secondary carbonate and epidote. Relict feldspar porphyroclasts
in the metapsammites are angular to subrounded
and display a wide range of grain sizes. Pebbleto cobble-sized clasts in the metaconglomerate
are composed of trondhjemite, vein quartz, and
metapsammite. Marble horizons, a distinctive
feature of the Tecomate Formation, occur as
intensely deformed, 1–2-m-thick tabular bodies
that are occasionally boudinaged. Apart from
abundant quartz veins, thin granitoid dikes are
localized to an area south of Santo Domingo
Tonahuixtla. Though lithologically identical to
the Tecomate Formation type area in the central Acatlán Complex (Ortega-Gutiérrez, 1978),
reconnaissance geochronological analyses of
Tecomate Formation metasedimentary rocks
from the field and the type area, respectively
(Keppie et al., 2004b; Sánchez-Zavala et al.,
2004), have yielded distinct detrital zircon age
populations, suggesting contrasting sources for
the two units.
U-Pb GEOCHRONOLOGY
Analytical Methods
Seven samples (see Table A1a1 and Fig. 3 for
locations) were collected for U-Pb zircon dating by LA-ICP-MS at the Laboratorio de Estudios Isotópicos (LEI), Centro de Geociencias,
Universidad Nacional Autónoma de México,
Mexico. Zircons were extracted using standard
mineral separation techniques, as described by
Solari et al. (2007). For details on the analytical
procedure, see GSA Data Repository file 1 (see
footnote 1).
In figures, tables, and results, 206Pb/238U ages
are quoted for zircons younger than 1.0 Ga,
whereas older grains are quoted using their
207
Pb/206Pb ages (e.g., Gehrels et al., 2006).
The latter ages become increasingly imprecise
younger than 1.0 Ga due to small amounts of
207
Pb. Zircon analyses with <10% normal and
<5% reverse discordance are considered to be
geologically meaningful (e.g., Harris et al.,
2004; Dickinson and Gehrels, 2008; Gehrels,
2012) and are used to date the time of intrusion
in igneous rocks or the maximum age of deposition in metasedimentary rocks. The latter is considered robust if it belongs to a cluster of three
of more zircons with similar ages (e.g., Gehrels
et al., 2006).
Results
Totoltepec Pluton
A sample of hornblende gabbro from one
of the lens-shaped bodies at the northeastern
margin of the Totoltepec pluton (TT-72) is composed of hornblende, plagioclase, epidote, and
chlorite, as well as accessory zircon, apatite, and
opaque minerals (Table A1a [see footnote 1]).
Zircons from the marginal mafic phase are
≤370 µm in length and exhibit uniform igneous oscillatory- and sector-zoning patterns. The
1
GSA Data Repository item 2012220, analytical
methods and tables of LA-ICP-MS geochronological and geochemical data, is available at http://www
.geosociety.org/pubs/ft2012.htm or by request to
[email protected].
analyses yielded 34 concordant 206Pb/238U ages
(Table A1b [see footnote 1]; Figs. 4A and 4B)
ranging from 299 ± 4 Ma to 311 ± 6 Ma. The
TuffZirc (Ludwig and Mundil, 2002) 206Pb/238U
age calculated from a coherent group of 25 zircon analyses is 306 ± 2 Ma.
The quartz diorite sample from the central
part of the Totoltepec pluton (TT-76B) consists
of oligoclase, quartz, muscovite, and chlorite,
with accessory apatite, zircon, and magnetite
(Table A1a [see footnote 1]). Zircons separated
from the dioritic phase are relatively small
(≤200 µm in length) and possess a complex internal texture with partially resorbed cores and
zircon overgrowths, as revealed by cathodoluminescence (CL) imaging. Zircon data (Table
A1c [see footnote 1]; Figs. 4C and 4D) range
from 278 ± 2 Ma to 310 ± 4 Ma, exhibiting a
slightly right-skewed distribution. The TuffZirc
algorithm yields a 206Pb/238U age of 289 ± 2 Ma
for a coherent group of 22 analyses.
Interpretation. The TuffZirc age of 306 ±
2 Ma is interpreted as the time of intrusion of
the Totoltepec hornblende gabbro. The other
two marginal bodies (Fig. 3), which are spatially proximal to the one dated and have similar
dimensions and petrologic characteristics, are
inferred to be coeval. The TuffZirc age of 289 ±
2 Ma is interpreted as the crystallization age of
the quartz diorite, corroborating earlier U-Pb
dating by Yañez et al. (1991) and Keppie et al.
(2004a), who reported concordant U-Pb zircon
ages of 287 ± 2 Ma and 289 ± 1 Ma for the intrusion of the Totoltepec pluton near Tonahuixtla,
respectively.
Tecomate Formation
Three metasedimentary samples from the
Tecomate Formation (TT-486A, TT-81, TT-82),
one sample from metasedimentary rocks previously mapped as the Cosoltepec Formation by
Ortega-Gutiérrez (1978) (TT-612), and a sample of a thin granitoid dike (TT-615) intruding
these metasedimentary rocks were collected
for geochronological analysis (Table A1a [see
footnote 1]; Fig. 3). Zircons from the psammitic
sample TT-486A (consisting of quartz, muscovite, K-feldspar, and opaque minerals) from the
Tecomate Formation in the northwestern part of
the study area, in the hanging wall just above
the fault contact with the Salada Unit (Fig. 3),
yielded only Proterozoic ages (Figs. 5A–5B;
Table A1d [see footnote 1]). Results show that
75% of the 99 concordant zircon analyses fall
in the age range between ca. 1014 and 1368 Ma.
The second-largest population consists of 17 zircons of early Mesoproterozoic age between ca.
1407 and 1629 Ma. The weighted mean age (incorporating both internal analytical and external
systematic error) of the youngest cluster over-
1611
Kirsch et al.
320
TT-72 Gabbro
B
n = 34
90–105% conc.
309 ± 2 Ma
300
(95.7% conf, n = 25)
290
Pb/ 206Pb
Relative probability
301 ± 2 Ma
100 µm
m
5
306 –1/+2 Ma
310
0.064
306 ± 2 Ma
10
TuffZirc 206Pb/ 238U age
0.060
0.056
207
15
Frequency
A
0.052
320
310
300
290
309 ± 2 Ma
0.048
2σ error ellipses
0
19.2
TT-76B Quartz Diorite
C
310 ± 2 Ma
286 ± 2 Ma
5
100 µm
289 ± 2 Ma
310
21.2
21.6
22.0
TuffZirc 206Pb/ 238U age
289 +1/–2 Ma
280
(94.8% conf, n = 22)
0.058
Pb/ 206Pb
285 ± 2 Ma
20.8
300
0.054
207
Frequency
10
20.4
290
278 ± 1 Ma
20.0
D
0.062
n = 40
90–105% conc.
15
19.6
320
310
300
290
280
0.050
294 ± 2 Ma
0.046
2σ error ellipses
0
270
280
290
300
310
320
19
20
Age (Ma)
21
238
22
U/
206
23
Pb
Figure 4. Histograms (A, C) as well as Tera-Wasserburg diagrams (B, D) for U-Pb laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) zircon analyses of Totoltepec pluton rocks; mean 206Pb/ 238U age calculated by TuffZirc age algorithm of Ludwig and
Mundil (2002). Black error bars are for the arguably syngenetic zircons, gray error bars for zircons likely to be xenocrystic, and white error
bars indicate analyses ignored due to anomalously high errors. Also displayed are cathodoluminescence images of representative zircon
crystals from dated rock samples.
lapping in age at 2σ, calculated using the DZ
Age Pick program developed at the LaserChron
Center of the University of Arizona (www.geo
.arizona.edu/alc), is 1005 ± 17 Ma (three grains).
A metapsammite assigned to the Tecomate
Formation in the eastern part of the field area
(TT-81) is composed mainly of quartz, plagioclase, muscovite, and opaque minerals. Zircons
separated from this sample yielded 79 concordant analyses ranging from 273 ± 10 Ma to
1796 ± 34 Ma (Figs. 5C–5D; Table A1e [see
footnote 1]). The most prominent population
is defined by 50 grains between the ages of ca.
277 and ca. 332 Ma. Three smaller populations
are defined by ages of ca. 400–570 Ma, ca. 780–
845 Ma, and ca. 925–1240 Ma, respectively.
The youngest cluster overlapping in age at 2σ
1612
error yields a weighted mean value of 288 ±
3 Ma (eight grains).
A metapelite sample (TT-82) from the
same area as TT-81 contains quartz, chlorite,
and muscovite, as well as accessory minerals. Ninety-seven concordant zircons from this
sample display an age span of 282 ± 2 Ma to
2621 ± 42 Ma (Figs. 5E–5F; Table A1f [see
footnote 1]), where a group of 16 grains with
ages between ca. 293 and ca. 313 Ma defines the
largest probability peak at ca. 303 Ma. Ages between ca. 905 Ma and 1230 Ma define another
significant age cluster, whereas age populations
of ca. 470–570 Ma and ca. 655–720 Ma are represented by 10 and 4 zircons, respectively. Two
zircon analyses with ages between ca. 362 and
ca. 385 Ma indicate a subordinate Devonian
source. The youngest cluster overlapping in age
at 2σ yields a weighted mean age of 299 ± 3 Ma
(six grains).
The metapsammite (TT-612) collected south
of Santo Domingo Tonahuixtla from a unit
originally mapped as the Cosoltepec Formation is primarily made up of quartz, plagioclase,
K-feldspar, and muscovite. Zircon analyses
from this sample (Figs. 5G–5H; Table A1g [see
footnote 1]) yielded 90 concordant ages ranging from 289 ± 2 Ma to 2708 ± 22 Ma. The
most dominant zircon population is made up
of ages between ca. 299 and ca. 326 Ma, yielding a probability peak at ca. 309 Ma. Another
major age population is defined by ages of ca.
950–1340 Ma. A smaller population has ages
between ca. 420 and ca. 605 Ma, and includes
0.13
TT-486A Metapsammite
A
20
1430–1590
0.076
1080
1040
1600
0.072
1000
960
0.09
5.4
1400
0.08
5.6
800
2σ error ellipses
0.06
2
C
TT-81 Metapsammite
309
10
5
925–1240
400–570
10
0.052
1600
280
290
300
310
320
330
330
320
310
300
290
280
270
0.048
1400
0.08
19.5
20.5
21.5
22.5
1200
1000
800
600
340
400
}
}
}
0.060
0.06
270
10
0.056
0
780–845
0.064
8
Weighted mean age =
288 ± 3 Ma
0.10
Pb/ 206Pb
288
D
207
20
6
0.068
1800
15
4
0.12
n = 79
90–105% conc.
30
Frequency
6.4
1000
0.07
0
40
2σ error ellipses
0.04
0
40
0
E
TT-82 Metapelite
303
470–570
282
905–1230
5
}
655–720
340
}
}
24
28
0.054
320
0.052
310
300
290
0.050
0.12
19.8
20.2
20.6
21.0
21.4
21.8
22.2
1400
0.08
320
20
0.16
0
300
16
Weighted mean age = 299 ± 3 Ma
0.060
1800
10
280
12
0.056
Pb/ 206Pb
20
8
0.058
207
Frequency
10
342
F
0.20
n = 97
90–105% conc.
30
4
0.062
1000
360
600
2σ error ellipses
0.04
0
0
TT-612 Metapsammite
G
10
5
950–1340
420–605
10
Pb/ 206Pb
20
H
8
12
16
20
24
28
0.064
0.060
207
Frequency
309
4
0.20
n = 90
90–105% conc.
30
0.16
0.056
340
0.052
330
320
310
300
290
0.12
19
1800
20
21
1400
0.08
}
0
300
310
320
330
1000
340
}
290
600
2σ error ellipses
0.04
0
0
4
8
12
16
20
24
28
0.068
TT-615 Granitoid dike
I
6
635
505–635
10
4
985–1310
2
0.056
Pb/ 206Pb
8
0.060
0.16
1800
}
}
0.08
300
310
320
330
330
320
310
19
20
12
16
300
290
21
1400
0
290
340
0.052
0.12
207
303
0.064
20
J
0.20
n = 57
90–105% conc.
323
Frequency
Figure 5. Relative age probability and histogram plots (A, C, E,
G, I) as well as Tera-Wasserburg
concordia diagrams (B, D, F,
H, J) for U-Pb laser ablation–
inductively coupled plasma–mass
spectrometry (LA-ICP-MS) zircon analyses of Chichihualtepec
Tecomate Formation metasedimentary rocks and a granitoid
dike. Black error ellipses in amplified concordia plot were used
for weighted mean age calculation of the youngest age group.
Histograms indicate number of
analyses within 100 m.y. interval; histograms of the youngest
age group have a 10 m.y. bin
width.
5.8
1200
}
10
1800
0.10
Pb/ 206Pb
Frequency
1265
Weighted mean age =
1005 ± 17 Ma
0.080
0.11
30
0.084
B
n = 99
90–105% conc.
1150
207
40
1000
340
600
2σ error ellipses
0.04
0
0
500
1000
1500
2000
2500
Age (Ma)
0
4
8
238
20
24
U/ 206Pb
1613
Kirsch et al.
a single Ordovician zircon of 469 ± 4 Ma. The
weighted mean of the youngest age cluster overlapping at 2σ error is 303 ± 3 Ma (five grains).
A sample of a thin granitoid dike (TT-615)
intruding the TT-612 Tecomate metapsammites
is principally composed of quartz, plagioclase,
and muscovite. In total, 57 concordant zircon
analyses exhibit an age range from 290 ± 2 Ma
to 2614 ± 22 Ma (Figs. 5I–5J; Table A1h [see
footnote 1]). The two most prominent probability peaks are defined by a group of 16 grains
with ages of ca. 294–316 Ma and by a group
of 11 zircons with ages of ca. 318–335 Ma,
followed by smaller age populations between
ca. 505 and 635 Ma and between ca. 985 and
1310 Ma. The youngest zircons that overlap
within 2σ error give a weighted mean age of
298 ± 3 Ma (five grains).
Interpretation. The ca. 1005 Ma age for the
youngest detrital zircons in sample TT-486A,
located near the stratigraphic base of the Tecomate Formation, suggests that this part of the
unit was deposited at a time when late Paleozoic igneous sources were not exposed. Similarly, the type Tecomate Formation yielded
no zircons younger than ca. 1.0 Ga (SánchezZavala et al., 2004).
U-Pb ages of detrital zircon grains in the other
samples are used to constrain the maximum depositional age of the Tecomate Formation in the
study area (e.g., Dickinson and Gehrels, 2009).
Of the three metasedimentary samples from the
Tecomate Formation south of the Totoltepec
pluton, TT-81 yields the youngest weighted
mean age (288 ± 3 Ma, Lower Permian), which
is taken to represent the maximum depositional
age in that locality. A 40Ar/39Ar whole-rock age
of 263 ± 3 Ma (Morales-Gámez et al., 2009)
from a Tecomate sericitic phyllite northwest of
the Totoltepec pluton provides a younger age
limit for the deposition of the Tecomate Formation as well as the age of metamorphism.
In another locality within the study area, the
depositional age of the Tecomate Formation is
more tightly constrained to ca. 300 Ma. Sample
TT-612 contains detrital zircons of Permian
age, so it is assigned to the Tecomate Formation rather than the Devonian–Carboniferous
Cosoltepec Formation, with which it was originally associated (Ortega-Gutiérrez, 1978). This
conclusion is consistent with field observations.
The weighted mean of the youngest age cluster
in sample TT-612 is 303 ± 3 Ma, which is similar within error to the weighted mean age of the
youngest zircon cluster from the granitoid dike
(298 ± 3 Ma) at the same locality, suggesting
that the host metapsammite in this locality was
deposited at ca. 300 Ma and intruded very soon
afterward. This depositional age is older than
the maximum depositional age obtained from
1614
sample TT-81. The ca. 298 Ma age falls between
the 306 ± 2 Ma age of the marginal gabbro and
the 289 ± 2 Ma of the central Totoltepec pluton,
suggesting that the dike is either a late phase
of the marginal gabbro or an early phase of the
main Totoltepec intrusion.
Whereas deposition of the Tecomate Formation south of the Totoltepec pluton occurred at
ca. 300 Ma in one location and between ca. 288
and ca. 263 Ma in another, fossiliferous limestone horizons in the type Tecomate Formation
in the central Acatlán Complex range from latest
Pennsylvanian to early Middle Permian (Keppie
et al., 2004b) and middle Pennsylvanian (Kazimovian = 306–304 Ma) to Early Permian. Thus,
the Tecomate Formation may be a composite
unit, collectively spanning the middle Pennsylvanian–Early Permian, but of different ages
in different locations. Nevertheless, these data
suggest that some of the Tecomate Formation in
the type area as well as in the study area was
deposited before intrusion and exhumation of
the Totoltepec pluton. To avoid confusion with
rocks in the type area, in this paper, the Tecomate Formation south of the Totoltepec pluton
is informally designated Chichihualtepec Tecomate Formation (CTF; Fig. 3).
Provenance of the Chichihualtepec Tecomate Formation. Taken together, there are 144
zircon grains in the age range between ca. 344
and ca. 273 Ma in analyzed samples from the
Chichihualtepec Tecomate Formation. A compilation of these ages (Fig. 6), including sensitive high-resolution ion microprobe (SHRIMP)
data of a sample from granite cobbles in Chichihualtepec Tecomate Formation metaconglomerates (Keppie et al., 2004b), shows that (1) the
distribution and range of ages are more or less
continuous, and (2) there is a significant overlap
between the detrital zircon age spectra and ages
obtained from samples of the Totoltepec pluton.
The measured Th/U ratios (Table A1 [see footnote 1]), which are >0.01, support a magmatic
origin of these zircons (e.g., Rubatto, 2002).
However, the Totoltepec pluton cannot be a
source of these zircons, as thermobarometric
data suggest that the pluton was at a depth of
~20 km at ca. 289 Ma, and 40Ar/39Ar data indicate it did not cool through the muscovite closure temperature until 283 ± 1 Ma (Kirsch et al.,
2012). Assuming this uplift rate of ~1.4 mm/yr
was maintained, the Totoltepec pluton was not
exposed until ca. 275 Ma. Zircons of Carboniferous–Permian age in parts of the Chichihualtepec Tecomate Formation that were deposited
before ca. 275 Ma therefore cannot have been
derived from the Totoltepec pluton, and are interpreted to have been derived from the regional
arc edifice and from epizonal plutons exposed
during the Pennsylvanian and Early Permian.
All of the U-Pb samples from the Chichihualtepec Tecomate Formation contain major
detrital zircon age peaks between ca. 920 and
1250 Ma, which are within the range of ages
documented from the adjacent Oaxacan Complex (Keppie et al., 2001, 2003; Solari et al.,
2003). Whereas ca. 600 Ma, 1500–1600 Ma,
1750–1900 Ma, and 2100–2500 Ma zircons
could have been derived from Amazonia, Oaxaquia, and/or Laurentia, those with 800–950 Ma
ages can come only from Amazonia (Keppie
et al., 2008a) or Oaxaquia (e.g., the ca. 917 Ma
Etla pluton; Ortega-Obregón et al., 2003). The
source for the five zircons with ages between
454 and 476 Ma may be the rift-related granitoid plutons within the Acatlán Complex, which
have yielded ages between 440 and 480 Ma
(Keppie et al., 2008b). Five detrital zircons in
the samples from the Chichihualtepec Tecomate
Formation are Devonian–Mississippian, spanning ages of 357–402 Ma. A postulated arc on
the western margin of the Mixteca terrane, most
of which was subsequently removed by subduction erosion (Keppie et al., 2008a, 2010), may
have been the source for these zircons.
GEOCHEMISTRY
Analytical Methods
In order to determine the tectonic setting for
the igneous and metasedimentary rocks in the
Totoltepec area, 34 samples from the Totoltepec pluton and 41 metasedimentary rocks of
the Tecomate Formation were analyzed for
major and selected trace elements (Fig. 3) by
X-ray fluorescence at the Regional Geochemical Centre, St. Mary’s University, Canada (for
details of analytical methods, see Dostal et al.,
1994). Of these, 15 representative samples from
the Totoltepec pluton and 7 from the Tecomate Formation were selected for analysis of
additional trace elements (rare-earth elements
[REEs], Y, Zr, Nb, Ba, Hf, Ta, and Th) by ICPMS according to methods described in Jenner
et al. (1990). Sm-Nd isotopic compositions of
these 15 samples were determined in order to
characterize the source regions and tectonic history of the respective geological units according
to the method described in Kerr et al. (1995).
For details on the analytical procedures, see
GSA Data Repository file 1 (see footnote 1).
Results
Results of the geochemical analyses are presented in Table A2 (see footnote 1). The samples
are affected to varying degrees by secondary
processes, including low-grade metamorphism
and deuteric alteration. These secondary processes have modified their primary chemical
Frequency
50
25
270
Totoltepec pluton
ca. 306 Ma Hbl gabbro
0
Totoltepec pluton
ca. 289 Ma Qz diorite
Pennsylvanian
PERMIAN
290
300
310
320
Mississippian
Age (Ma)
CARBONIFEROUS
Early Permian
n = 162
280
330
340
TT-81
Metapsammite
TT-82
Metapelite
TT-612
Metapsammite
TT-615
Granitoid dike
350
TEC-10
Granite cobble
metaconglomerate
(Keppie et al., 2004b)
Rel. prob
Figure 6. A 2σ error bar plot showing concordant 206Pb/ 238U ages of detrital zircons from the Chichihualtepec Tecomate Formation metasedimentary rocks. Data also include inherited zircons extracted from a granitoid dike intruding Chichihualtepec Tecomate Formation
metapsammites as well as U-Pb sensitive high-resolution ion microprobe (SHRIMP) analyses of zircons separated from Chichihualtepec
Tecomate Formation metaconglomerate granitoid cobbles (Keppie et al., 2004b). Diagonally hatched regions and histograms represent
U-Pb age data from Totoltepec pluton rocks. Gray shaded histogram on the right-hand side shows the age distribution of all detrital zircon
data featured in this diagram. Qz—quartz; Hbl—hornblende.
composition, resulting in a scatter on diagrams
featuring alkali and alkaline earth elements and
elevated loss on ignition (LOI) values. Hence,
inferences about the petrogenesis of the rocks
are largely based on high field strength elements
(HFSEs) and rare earth elements (REEs), which
are considered to be relatively “immobile” during alteration processes (e.g., Winchester and
Floyd, 1977), and should reflect original magma
chemistry for the igneous rocks as well as provenance compositions of the sedimentary rocks
(Taylor and McLennan, 1985).
Totoltepec Pluton
Geochronological data indicate that the
Totoltepec pluton was formed in two distinct
intrusive events. Hence, geochemical data for
rocks from the ca. 306 Ma marginal bodies and
for rocks from the ca. 289 Ma main body of the
pluton are presented separately.
Older (ca. 306 Ma) Totoltepec rocks. Samples
from the older marginal bodies of the Totoltepec
pluton range from hornblende gabbro to hornblendite with SiO2 (LOI-free) between 41.9 and
51.1 wt%. These mafic to ultramafic rocks have
relatively wide ranges in TiO2 (0.19–0.99 wt%),
Fe2O3 (2.89–12.6 wt%), MgO (2.45–11.3 wt%),
Cr (38–313 ppm), V (66–434 ppm), Co (11–
47 ppm), and Ni (21–163 ppm) (Fig. 7; Table A2a
[see footnote 1]). The samples have low Nb/Y
(0.03–0.15) and Zr/Ti (0.002–0.009), which is
typical of subalkaline basaltic rocks (Fig. 8). The
rocks are characterized by low Th/Yb and Ta/Yb
and highly variable Th/Hf ratios. On discrimination diagrams using these parameters, the data
straddle the boundary between calc-alkaline and
island-arc tholeiitic fields (Figs. 9A and 9B).
The hornblende gabbros exhibit relatively flat
chondrite-normalized REE patterns (Fig. 10A;
average [La/Yb]n = 1.8) with ΣREE of 3–13
times chondrite, and positive Eu anomalies (up to
Eu/Eu* = 2.6) that decrease with increasing SiO2.
The presence of pronounced positive Eu anomalies in some gabbro samples suggests plagioclase accumulation. The hornblendite sample is
characterized by a concave-upward REE pattern
([La/Sm]n = 0.4; [Gd/Yb]n = 1.7), indicative of
the dominance of cumulus amphibole.
The mid-ocean-ridge basalt (MORB)–normalized multi-element plot of the ca. 306 Ma
marginal rocks (Fig. 10B) shows enrichment
in large ion lithophile elements (LILEs; Cs,
Rb, Ba, U, K, Pb, and Sr), moderate depletion
in the less incompatible elements (Zr, Hf, Ti,
middle to heavy REEs), and strong depletion
in the HFSEs Nb and Ta. This signature reflects
derivation from a mantle wedge affected by slab
fluxing processes, i.e., patterns that are typical
of subduction-related magmas (e.g., Saunders
et al., 1988; McCulloch and Gamble, 1991).
Sm-Nd isotope analyses on the older marginal
Totoltepec rocks yield initial εNd ranging from
+1.3 to +3.3 and 147Sm/144Nd ratios from 0.15 to
0.24 with a TDM model age (147Sm/144Nd < 0.165;
Stern, 2002) of 0.84 Ga (Table 1; Fig. 11). The
306 Ma sample (TT-72) with the lowest εNd (i)
plots well above the mantle depletion-enrichment array in Figure 9A and toward the Th
apex in Figure 9B, indicating contamination by
a crustal or a subduction component. Accordingly, on the εNd (t) versus 147Sm/144Nd diagram
(Fig. 11B), this sample lies on a curve representing assimilation and fractional crystallization (DePaolo, 1981) between one of the more
juvenile 306 Ma samples and the average composition of the Oaxacan Complex (Ruiz et al.,
1988). By contrast, the Sm-Nd isotopic signature of the other hornblende gabbro samples as
well as the hornblendite is similar to Ordovician
mafic rocks within the Mixteca terrane (Murphy
et al., 2006; Ortega-Obregón et al., 2010), which
are interpreted to have been derived from a ca.
1.0 Ga subcontinental lithospheric mantle. The
306 Ma gabbro and hornblendite may hence
1615
TiO2 (wt%)
0.8
30
Al2O3 (wt%)
289 Ma
1.0
Quartz-rich granitoid
Trondhjemite
Plag-rich cumulate
Tonalite
Quartz diorite
Hornblende diorite
306 Ma
Kirsch et al.
Hornblende gabbro
Hornblendite
25
0.6
20
0.4
15
0.2
A
B
0
15
CaO (wt%)
K2O (wt%)
High K
10
Medium K
1
Low K
5
C
0.1
0
Zr (ppm)
D
La Carbonera
(275 Ma)
(La/Yb)n
Chiapas Massif
(272–251 Ma)
100
10
Cozahuico granite
(270 Ma)
10
Tuzancoa
(290–260 Ma)
Cuchumatanes
(318–313 Ma)
1
E
F
45
50
55
60
65
70
75
45
50
SiO2 (wt%)
55
60
65
70
75
SiO2 (wt%)
Figure 7. Variation diagrams for selected major elements, high field strength trace elements, and ratios of Totoltepec pluton rocks and correlative Carboniferous–Permian igneous suites (labeled in part F). Division lines in K2O plot are from Le Maitre et al. (2002). Included in
the comparison (from north to south) are geochemical data from (1) andesitic to basaltic lava flows from the 290–260 Ma Tuzancoa Formation in the Sierra Madre terrane (Rosales-Lagarde et al., 2005); (2) the 270 ± 3 Ma Cozahuico granite (this paper), which intrudes the N-S
dextral transpressive Caltepec fault zone (CFZ); (3) the 275 ± 4 Ma La Carbonera stock, which intrudes the northern Oaxacan Complex
(Solari et al., 2001; this paper); (4) ca. 272–251 Ma orthogneisses of the Chiapas Massif (Maya block; Weber et al., 2005); and (5) ca. 318–
313 Ma plutons in the Altos Cuchumatanes Range, Guatemala (Maya block; Solari et al., 2010; Solari, 2012, personal commun.).
be derived from the same subcontinental lithospheric mantle as the Ordovician mafic rocks.
Mafic rocks with similar isotopic compositions
also occur along other parts of the Gondwanan
margin (Avalonia: e.g., Murphy and Dostal,
2007; Iberia-western Europe: e.g., Murphy
et al., 2008; Keppie et al., 2011), suggesting the
1616
subcontinental lithospheric mantle that underlay
the area in the late Paleozoic may have been regionally widespread.
Main-phase (ca. 289 Ma) Totoltepec rocks.
Totoltepec pluton samples of ca. 289 Ma age
consist of hornblende diorite, tonalite, quartz
diorite, trondhjemite, quartz-rich granitoid, and
plagioclase-rich cumulates from the main body
of the pluton. Trondhjemite dikes that intrude
the ultramafic and mafic marginal bodies of the
pluton are included in the ca. 289 Ma Totoltepec
rocks based on matching petrographic and geochemical characteristics. The samples display a
wide range in chemistry, with an SiO2 content
0.1
1
10
40
50
60
0.001
0.01
Alkali basalt
Subalkaline
basalt
Andesite
Phonolite
Zr/ TiO2
0.1
Basanite
Trachybasanite
Nephelinite
TrAn
Trachyte
1
Cuchumatanes 318–313 Ma
Tuzancoa 290–260 Ma
La Carbonera 275 Ma
Chiapas Massif 272–251 Ma
Cozahuico granite 270 Ma
Hornblende gabbro
Hornblendite
289 Ma
306 Ma
Com/Pan
Trondhjemite
Plag-rich cumulate
Tonalite
Quartz diorite
Hornblende diorite
Rhyolite
10
Zr/Ti
0.1
1
0.01
0.001
0.01
Subalkaline
Basalt
Andes. +
bas. andes.
Rhyolite +
dacite
B
0.1
Nb/Y
1 Alkaline
Alkali
basalt
Trachyandesite
Trachyte
Alkali rhyolite
10
Foidite
IAT
CAB
CAB
SHO
A
Ta/Yb
1
Hornblende gabbro
Hornblendite
10
Trondhjemite
Plag-rich cumulate
Tonalite
Quartz diorite
Hornblende diorite
ALK
Th
SZ
UC
/Th
Hf
=3
D
B
C
LC
B
A
MM
Hf/3
C
Ta
0.01
0.1
1
0.1
Cozahuico granite
(270 Ma)
La Carbonera
(275 Ma)
syn-COLG
1
WPG
ORG
10
Yb (ppm)
Chiapas Massif
(272–251 Ma)
VAG
Tuzancoa
(290–260 Ma)
Cuchumatanes
(318–313 Ma)
Figure 9. Tectonic discrimination diagrams for rocks of the Totoltepec pluton and comparative igneous suites (see caption of Fig. 7 for references). (A) Th/Yb versus Ta/Yb diagram
identifying mantle source and subduction components (modified after Pearce, 1982, 1996). Compositional fields: TH—tholeiitic; TR—transitional; ALK—alkaline; CA—calcalkaline; SHO—shoshonitic. Compositions of normal mid-ocean-ridge basalt (N-MORB), enriched (E) MORB, and ocean-island basalt (OIB) are after Sun and McDonough (1989);
(B) Th-Hf/3-Ta discrimination diagram after Wood et al. (1979). MM—mantle source; UC—upper crust; LC—lower crust; SZ—subduction component. (C) Yb versus Ta diagram
for felsic rocks (after Pearce et al., 1984). VAG—volcanic arc granites; syn-COLG—syncollision granites; WPG—within-plate granites; ORG—ocean-ridge granites.
0.1
NMORB
TH
EMORB
TR
OIB
A = N-MORB
B = E-MORB and
within-plate tholeiites
C = Alkaline within-plate
basalts
D = Destructive
plate-margin basalts:
island arc tholeiites
(Hf/Th > 3) and
calc-alkaline basalts
(Hf/Th < 3)
Ultraalkaline
Tephryphonolite
Phonolite
Figure 8. Geochemical rock classification of samples from the Totoltepec pluton and other igneous suites of similar age (see caption of Fig. 7
for references). (A) Zr/TiO2-SiO2 diagram and (B) bivariate Nb/Y versus Zr/Ti diagram (after Winchester and Floyd, 1977; Pearce, 1996).
0.01
0.01
SiO2 (wt%)
Rhyodacite
Dacite
289 Ma
306 Ma
Th/Yb
Evolved
Intermediate
Basic
70
A
Ta (ppm)
80
1617
Kirsch et al.
A
100
1000
B
100
10
0.1
0.01
1
Sample / chondrite
Sample / NMORB
1
10
0.001
C
100
1000
D
100
10
0.01
La Carbonera 275 Ma
Tuzancoa 290–260 Ma
Trondhjemite
Plag-rich cumulate
Tonalite
Quartz diorite
Hornblende diorite
306 Ma
Chiapas Massif 272–251 Ma
289 Ma
0.1
Sample / NMORB
1
1
Sample / chondrite
10
Hornblende gabbro
Hornblendite
0.001
1000
E
100
F
100
10
0.1
0.01
1
Sample / chondrite
Sample / NMORB
1
10
0.001
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Cs Rb Ba Th U Nb Ta K La Ce Pb Pr Sr P Nd Zr Hf Sm Eu Ti Dy Y Yb Lu
Figure 10. Chondrite-normalized rare earth element (REE) patterns (A, C, E) and normal mid-ocean-ridge basalt (N-MORB)–normalized
multi-element plots (B, D, F) for Totoltepec pluton rocks and comparative igneous suites (see caption of Fig. 7 for references). Normalizing
values are from Sun and McDonough (1989).
(LOI-free) spanning 51.6–77.7 wt% and Mg#
(100 × Mg/[Mg + Fe] molar) of 21–63. With
increasing silica, the samples show a decrease
in TiO2, Al2O3, CaO (Fig. 7), and Ni, suggesting that these rocks may represent a comagmatic series with fractionating plagioclase and
hornblende. When plotted against SiO2, P2O5,
Zr, Nb, and Ce display convex-upward patterns,
1618
indicating fractionation of apatite, zircon, and
other accessory phases. The 289 Ma Totoltepec
rocks are characterized by low abundances of
Cr (≤27 ppm), V (≤288 ppm), Co (≤29 ppm),
and Ni (≤19 ppm). On the Zr/TiO2-SiO2 diagram
(Fig. 8A; Winchester and Floyd, 1977; Pearce,
1996), the samples are classified as mafic to
felsic in composition, and their low Zr/Ti ratios
are typical of subalkaline mafic to intermediate
rocks (Fig. 8B). Their subalkaline character is
also indicated by their low Nb/Y (0.02–0.49)
values as well as their position above the mantle
array in the Ta/Yb versus Th/Yb plot (Fig.
9A). A volcanic arc origin is indicated on the
Th-Hf-Ta and Yb versus Ta diagrams (Figs. 9B
and 9C), and by Zr/Nb (~30), Ce/Yb (~12), and
TABLE 1. Sm-Nd ISOTOPIC DATA FOR SAMPLES FROM THE TOTOLTEPEC AREA, ACATLÁN COMPLEX, MEXICO
Nd
Sm
T(i)
147
143
Rock type
(ppm)
(ppm)
Sm/Nd
Sm/144Nd
Nd/144Nd
2σ
(Ma)
εNd (0)*
εNd (i)
Sample
Totoltepec pluton
Ca. 306 Ma marginal rocks
TT-24
Hornblende gabbro
TT-26A
Hornblende gabbro
TT-26B
Hornblende gabbro
TT-28
Hornblendite
TT-72
Hornblende gabbro
TDM†
(Ga)
1.77
1.58
2.07
4.44
6.45
0.60
0.40
0.71
1.74
1.86
0.340
0.256
0.344
0.391
0.288
0.2054
0.1548
0.2077
0.2365
0.1743
0.512811
0.512722
0.512813
0.512858
0.512659
10
20
10
6
7
306
306
306
306
306
3.4
1.6
3.4
4.3
0.4
3.0
3.3
3.0
2.7
1.3
–
0.84
–
–
(1.47)
Ca. 289 Ma rocks
TT-12§
TT-13A
Tonalite
TT-13B
Tonalite
TT-14
Hornblende diorite
TT-16
Trondhjemite
TT-22
Trondhjemite
TT-27
Trondhjemite
TT-52
Plagioclase-rich cumulate
TT-74
Trondhjemite
TT-78
Tonalite
1.06
7.58
10.23
10.05
2.03
7.51
1.23
1.90
3.07
9.22
0.04
1.98
3.08
2.60
0.47
1.64
0.40
0.44
0.61
2.37
0.035
0.261
0.301
0.259
0.233
0.219
0.327
0.234
0.199
0.257
0.0213
0.1578
0.1821
0.1562
0.1405
0.1322
0.1973
0.1416
0.1202
0.1556
0.512523
0.512642
0.512677
0.512690
0.512561
0.512528
0.512747
0.512492
0.512458
0.512691
8
5
7
7
7
6
8
7
4
7
289
289
289
289
289
289
289
289
289
289
-2.2
0.1
0.8
1.0
–1.5
–2.1
2.1
–2.8
–3.5
1.0
4.2
1.5
1.3
2.5
0.6
0.2
2.1
–0.8
–0.7
2.6
(0.42)
1.09
(1.74)
0.94
1.00
0.97
(2.89)
1.16
0.96
0.93
Chichihualtepec Tecomate Formation (CTF)
TT-5A
Metapsammite
TT-6
Metapelite
TT-7B
Metapsammite
TT-36
Metapsammite
TT-39
Metapsammite
TT-61A
Metapsammite
TT-67
Meta-arkose
13.62
22.03
23.25
16.81
26.36
39.88
16.91
3.13
5.14
4.96
4.06
4.80
7.74
3.51
0.230
0.233
0.213
0.241
0.182
0.194
0.208
0.139
0.1411
0.129
0.1459
0.0988
0.1173
0.1255
0.512520
0.512396
0.512299
0.512558
0.512168
0.512308
0.512319
7
8
6
7
4
5
8
288
288
288
288
288
288
288
–2.3
–4.7
–6.6
–1.6
–9.2
–6.4
–6.2
–0.2
–2.7
–4.1
0.3
–5.6
–3.5
–3.6
1.07
1.35
1.33
1.09
1.16
1.16
1.25
Cozahuico granite
TT-560
Granite
TT-563
Granite
TT-564
Granite
5.08
7.01
10.82
1.02
1.64
1.79
0.200
0.233
0.166
0.1206
0.1411
0.1002
0.512313
0.512384
0.512287
7
7
7
270
270
270
–6.3
–5.0
–6.8
–3.7
–3.0
–3.5
1.19
1.37
1.02
La Carbonera Stock
TT-565A
Diorite
17.71
3.34
0.188
0.1139
0.512303
7
275
–6.5
–3.6
1.13
TT-565B
Diorite
23.72
4.88
0.206
0.1243
0.512336
7
275
–5.9
–3.4
1.20
Gabbro
71.64
18.70
0.261
0.1578
0.512338
7
275
–5.9
–4.5
1.91
TT-568
TT-569
Granodiorite
22.29
3.782
0.170
0.1026
0.512311
6
275
–6.4
–3.1
1.00
Note: Analyses were performed at the Atlantic Universities Regional Isotopic Facility, Memorial University of Newfoundland. For details on analytical procedures, see GSA
Data Repository File 1 (see text footnote 1).
*εNd values are relative to 143Nd/144Nd = 0.512638 and 147Sm/144Nd = 0.196593 for present-day chondrite uniform reservoir (CHUR; Jacobsen and Wasserburg, 1980) and
λ147Sm = 6.54 × 10–12/yr (Steiger and Jäger, 1977).
†
Depleted mantle model ages (TDM ) were calculated using the depleted mantle model of DePaolo (1981). Values in parentheses denote model ages that may be unreliable
due to high 147Sm/144Nd (>0.165; Stern, 2002).
§
Sample has anomalously low Sm and Nd concentrations and is thus excluded from further consideration.
La/Nb (~3) ratios, which are typical of modern
calc-alkaline suites (Gill, 1981; Pearce, 1982;
Cabanis and Lecolle, 1989). However, some of
the samples exhibit a more primitive tholeiitic
character due to lower Th/Yb (Fig. 9A) and
higher Hf/Th (Fig. 9B) ratios.
The chondrite-normalized REE patterns of the
ca. 289 Ma diorite and tonalite samples (Fig. 10C)
are characterized by flat light (L) REEs (average
[La/Sm]n = 1.5), flat to moderately fractionated
heavy (H) REEs ([Gd/Yb]n = 1.1–3.3), small negative to small positive Eu anomalies (Eu/Eu* =
0.7–1.4), and ΣREE abundances of 12–21 times
chondrite. Chondrite-normalized REE patterns
of the trondhjemites, and samples of quartz-rich
granitoid and plagioclase-rich cumulate (Fig.
10E) are typified by an LREE enrichment (average [La/Sm]n = 2.7; average [La/Yb]n = 4.6), flat
HREE patterns (average [Gd/Yb]n = 1.2), negative to positive Eu anomalies (Eu/Eu* = 0.5–2.9),
and low ΣREE. The general trend for these samples is a decrease in ΣREE with increasing SiO2,
which may be an effect of accessory phase fractionation (Miller and Mittlefehldt, 1982).
Multi-element patterns for diorite and tonalite
normalized to N-MORB (Fig. 10D) show enrichment in LILEs (Cs, Ba, K, Pb, and Sr) and
moderate depletion in the HFSEs Ta and Ti.
Abundances of Nb, Zr, and Hf as well as the
middle REEs are similar to N-MORB. The
heavy REEs are depleted in all but one tonalite
sample, which exhibits HREE values identical
to N-MORB. Trace-element profiles (Fig. 10F)
for the Totoltepec trondhjemites, and samples
of quartz-rich granitoid and plagioclase-rich
cumulate are enriched in strongly incompatible elements (Cs, Rb, Ba, Th, U), moderately
depleted in the less incompatible elements
(middle to heavy REEs, Ti, Y), and show strong
Nb and Ta negative anomalies. These patterns
are a characteristic feature of arc magmas (e.g.,
Pearce and Peate, 1995).
The Sm-Nd isotopic data for the ca. 289 Ma
Totoltepec rocks yield initial εNd values between
–0.8 and +2.6 and 147Sm/144Nd ratios from 0.12 to
0.20 (Table 1; Fig. 11). Rocks with 147Sm/144Nd <
0.165 yield TDM ages of 0.93–1.16 Ga. Although
considerably less radiogenic than the contemporary depleted mantle, one of the ca. 289 Ma tonalite samples (εNd [i] = 2.6) and the hornblende
diorite (εNd [i] = 2.5) have similar isotopic compositions to those of the ca. 306 Ma mafic rocks,
suggesting derivation from the same subcontinental lithospheric mantle. The other ca. 289 Ma
Totoltepec rocks exhibit lower εNd (i) and higher
TDM values. These rocks could not have originated by simple differentiation of a Totoltepec
pluton mafic parent, because simple fractional
crystallization should not affect the 143Nd/144Nd
ratio. Their position along assimilation and fractional crystallization (AFC) trajectories in the
εNd (t) versus 147Sm/144Nd diagram (Fig. 11B)
suggests that their isotopic signature may be
an effect of mixing between a basaltic magma
(P) and crustal melts (C) derived from Oaxacan
Complex basement.
1619
Kirsch et al.
Figure 11. (A) ε Nd (t) versus
Deplete
d
time plot comparing Sm-Nd
mantle
isotopic data of the Totoltepec
pluton (vertically hatched) and
5
the Chichihualtepec Tecomate
Formation metasedimentary
rocks (diagonally hatched) with
metasedimentary rocks from
the Tecomate Formation type
0
area (Yañez et al., 1991), rocks
Totoltepec pluton
from the Oaxacan Complex
(Ruiz et al., 1988), and OrdoChichihualtepec Tec. Fm.
vician amphibolites from the
Metapelite
Asis area (Murphy et al., 2006).
Metapsammite
Modern depleted mantle com5
Meta-arkose
position is from DePaolo (1988).
147
144
Asis
amphibolites
(B) Sm/ Nd versus ε Nd (t)
diagram for Totoltepec pluton
Tecomate Fm. type area
rocks as a means to evaluate
Oaxacan Complex
crustal contamination. Fields correspond to Sm-Nd data from the
10
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Cozahuico granite (this paper;
Elías-Herrera et al., 2005;
t (Ga)
Trondhjemite
Torres et al., 1999), the La CarPlag-rich cumulate
bonera stock (this paper), the
8
Tonalite
Depleted
Altos Cuchumatanes granitoids
mantle
Quartz
diorite
(Solari, 2012, personal comHornblende diorite
6
mun.), the Tuzancoa Formation
volcanic rocks (Rosales-Lagarde
Hornblende gabbro
Plag
Ol, Px, Hbl
et al., 2005), and Ordovician
Hornblendite
4
amphibolites from the Asis
lithodeme (Murphy et al., 2006)
P
2
and the Olinalá area (Ortegar = 0.25
Obregón et al., 2010). For
comparison, εNd (t) data for all
0
samples are shown at t = 289 Ma.
The black curves show trends
r = 0.75
-2
for assimilation and fractional
La Carbonera 275 Ma
crystallization (AFC; DePaolo,
r = 10
1981) in which crust (C—aver-4
Ord. amphibolites Olinalá
age composition of the Oaxacan
(Ortega-Obregon et al., 2010)
r=2
Complex calculated from Ruiz
Ord. amphibolites Asis
-6
Oaxacan
(Murphy et al., 2006)
et al., 1988) is assimilated by
Complex
Totoltepec pluton trondhjemite
a basaltic parent magma (P—
(Martiny-Kramer, 2008)
Ol, Px, Ap, Zrc C
K-fsp, Plag
average composition of four
-8
most juvenile 306 Ma marginal
0.10
0.12
0.14
0.16
0.18
0.20
0.22
0.24
ultramafic to mafic rocks of the
147
Sm/144Nd
Totoltepec pluton). Values for r
(rate of assimilation relative to fractional crystallization) are indicated adjacent to AFC lines. For r ≥ 1, curves extend to values of F (fraction
of remaining liquid) = 5; for r < 1, curves end at F = 0.1. Partition coefficients are from Arth (1976). Composition of depleted mantle is from
DePaolo (1988). Gray arrows indicate trends for pure fractional crystallization of olivine (Ol), pyroxene (Px), hornblende (Hbl), plagioclase
(Plag), apatite (Ap), zircon (Zrc), and K-feldspar (K-fsp).
εNd(t = 289 Ma)
306 Ma
B
289 Ma
εNd(t)
A
Comparative Geochemistry
In order to evaluate their regional significance, we compare the Totoltepec rocks to other
Permian to Carboniferous igneous suites along
the North American Cordillera for which ages
have been determined by U-Pb geochronology
1620
(Figs. 2 and 7). Some of these suites form part of
the putative late Paleozoic continental magmatic
arc extending along the length of Mexico (e.g.,
Torres et al., 1999; Centeno-García, 2005).
Harker diagrams display considerable overlap between the Totoltepec pluton and the com-
parative suites for major elements TiO2, Al2O3,
Fe2O3, and CaO (Fig. 7), but the Cozahuico granite, La Carbonera stock, and igneous rocks from
the Chiapas Massif and the Altos Cuchumatanes
exhibit consistently higher SiO2 and K2O. The
more felsic and more alkalic character of these
exhibit an εNd (t) value of –1.3 (t = 275) and a
TDM model age of 1.4 Ga (recalculated from
Rosales-Lagarde et al., 2005). These values,
which are less radiogenic than Totoltepec pluton
rocks with similar SiO2 content, suggest derivation by melting of older continental crust. This
conclusion is consistent with an abundance of
inherited zircons and/or crustal xenoliths documented in these rocks (Elías-Herrera et al., 2005;
Solari et al., 2001, 2010). Other plutonic rocks,
for which their late Paleozoic ages are based on
K-Ar or Rb-Sr dating (not shown), as well as
sedimentary rocks of Permian–Carboniferous
age exhibit εNd (i) values similar to the Cozahuico and La Carbonera stocks (Torres et al.,
1999; Schaaf et al., 2002; Yañez et al., 1991)
and therefore are in broad agreement with this
interpretation.
suites is also apparent in the rock classification
diagrams (Fig. 8), where they plot mainly in the
fields of (trachy-)andesite, rhyolite, and trachyte.
Lavas from the Tuzancoa Formation overlap the
composition of Totoltepec pluton tonalite and
quartz diorite. Tectonic discrimination diagrams
(Fig. 9) classify the majority of the samples from
the comparative igneous suites as calc-alkaline
arc rocks, but they show higher Ta and Yb abundances as well as higher Ta/Yb and Th/Yb ratios
than rocks of the Totoltepec pluton. Chondritenormalized REE patterns of comparative igneous suites are more fractionated (higher[La/Yb]n
ratios; Figs. 7F, 10A, 10C, and 10E), and they
display higher total REE abundances than most
samples of the Totoltepec pluton. The MORBnormalized spidergrams of comparative igneous
suites (Figs. 10B, 10D, and 10F) are similar
to those of rocks from the Totoltepec pluton,
showing a jagged pattern with positive LILE
enrichment and negative HFSE anomalies, typical of arc-derived rocks. On average, however,
the Totoltepec rocks have lower abundances of
Nb, Ta, Zr, and LREE, and are less enriched in
LILEs (Rb, Th, K) than comparative Carboniferous–Permian igneous rocks. The Sm-Nd
isotopic signature of the Cozahuico, La Carbonera, and the Altos Cuchumatanes rocks is less
radiogenic than that of the Totoltepec pluton,
displaying initial εNd values between –4.9 and
–3.0, TDM model ages from 1.1 to 2.2 Ga, and
147
Sm/144Nd ratios between 0.10 and 0.16 (Fig.
11; this paper: Table 1; Torres et al., 1999; ElíasHerrera et al., 2005; Solari, 2012, personal commun.). The Tuzancoa Formation volcanic rocks
Andesitic
arc source
La/Th
10
8
Mixed felsic-basic source
6
Acid arc source
4
Passive
margin
source
2
0.35
B
0.30
OIA
Al2O3 / SiO2 (wt%)
Tholeiitic oceanic
arc source
12
Chichihualtepec Tecomate Formation
Samples from the Chichihualtepec Tecomate
Formation collected for geochemistry include
16 metapsammites, 11 metapelites, 12 metaarkoses, and 2 metaconglomerates. The majorelement abundances of these metasedimentary
rocks lie in the range of typical shales, sandstones, and graywackes, with their SiO2 content
ranging from 56.4 to 76.9 wt% and Al2O3 values
from 11 to 21 wt% (LOI-free basis). SiO2 displays negative correlations with Al2O3 (correlation coefficient r = –0.84), Fe2O3 (r = –0.92), Co
(r = –0.84), and V (r = –0.80), respectively, which
reflect the different proportions of clay/mud-rich
and quartz-rich components, as documented in
other sedimentary sequences (e.g., Bhatia, 1983).
Metapelite
Metapsammite
Meta-arkose
Metaconglomerate
Upper continental crust
North American Shale Composite
Post Archean Australian Shale
A
14
The range of Al2O3/TiO2, Cr/Th, Th/Co,
Cr/V, and V/Ni ratios in the Chichihualtepec
Tecomate Formation rocks suggests that the
majority of samples are derived from felsic
sources (Taylor and McLennan, 1985; Cullers,
1994; Girty et al., 1996), which is consistent
with the low average MgO, Fe2O3, Cr, Ni, and
Co abundances. Incompatible elements such as
Zr, Nb, Hf, Ta, Y, Th, and U have higher abundances in the Chichihualtepec Tecomate Formation rocks than they display in sedimentary
suites derived from mafic sources (Feng and
Kerrich, 1990). Similarly, Hf and La/Th characteristics of the Chichihualtepec Tecomate Formation rocks (Floyd and Leveridge, 1987; Fig.
12A) indicate an acid arc to mixed felsic-basic
source with a minor influence of older sedimentary components.
Chondrite-normalized REE patterns of the
Chichihualtepec Tecomate Formation (Fig.
13A) are characterized by a moderate enrichment in LREE ([La/Yb]n = 3.0–7.1), flat
HREE ([Gd/Yb]n = 1.0–1.5), and negative Eu
anomalies (Eu/Eu* = 0.62–0.82). These features suggest that the source of the clastic rocks
was fractionated with respect to plagioclase
(Slack and Stevens, 1994). One metapsammite
sample exhibits a greater REE fractionation
(LREE/HREE = 16.9, [La/Yb]n = 25.0) and a
slightly steeper HREE slope ([Gd/Yb]n = 2.5).
Total REE abundances for all samples range between 20 and 150 times chondrite.
The Sm-Nd isotopic compositions for Chichihualtepec Tecomate Formation samples are
highly variable (Fig. 11A), with εNd (t) values
0.25
CA
0.20
ACM
0.15
0.10
PM
OIA – Oceanic island arc
CA – Continental island arc
ACM – Active continental margin
PM – Passive margin
0.05
Increasing old sediment component
0
0
0
2
4
6
8
10
12
14
0
2
4
Hf (ppm)
6
8
10
12
14
16
(Fe2O3+MgO) (wt%)
Figure 12. Discrimination diagrams for the metasedimentary rocks of the Chichihualtepec Tecomate Formation. (A) Hf versus La/Th diagram
after Floyd and Leveridge (1987); (B) (Fe2O3 + MgO) versus (Al2O3/SiO2) diagram after Bhatia (1983). Post-Archean Australian Shale, upper
continental crust (Taylor and McLennan, 1985), and North American Shale Composite (Gromet et al., 1984) are shown for comparison.
1621
Kirsch et al.
Sample / chondrite
Tecomate Formation (Fig. 13B) rocks are characterized by positive Cs, Ba, and U anomalies
for some samples and a strong depletion in
HFSEs, particularly Nb and Ta. This signature
suggests that the Chichihualtepec Tecomate
Formation was deposited in a sedimentary basin
that formed in an arc environment. An arc-related provenance is also indicated on the Hf versus La/Th plot (Floyd and Leveridge, 1987; Fig.
12A) and the (Fe2O3 + MgO) versus Al2O3/SiO2
ratio diagram (Bhatia, 1983; Fig. 12B). A limited range in Ti/Zr ratios and the petrographic
observations, such as the high modal abundance
of feldspar, a wide range of grain sizes, and the
angularity of relict porphyroclasts, point to a
compositionally immature, poorly sorted sediment that was only transported over a short distance (Garcia et al., 1994).
Metapsammite
Meta-arkose
Metapelite
100
UC
(Taylor and McLennan,1985)
10
A
1
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
SUMMARY AND DISCUSSION
10
Samples / upper continental crust
Our results indicate that the late Paleozoic
Totoltepec pluton and the metasedimentary
Chichihualtepec Tecomate Formation postdate
collisional orogenesis and developed at different crustal levels along the periphery of Pangea.
The Totoltepec pluton consists of minor maficultramafic rocks (306 ± 2 Ma) that are marginal
to the main felsic-mafic intrusion (289 ± 2 Ma).
Both intrusive phases have an arc geochemistry
but are more primitive than contemporaneous
arc complexes in southern Mexico. The Chichihualtepec Tecomate Formation was derived
from a late Paleozoic arc.
1
0.1
B
Cs Rb Ba Th U Nb Ta K La Ce Pr Sr Nd Zr Sm Eu Ti Dy Y Yb Lu Hf Tb Tm Gd Ho Er
Figure 13. (A) Chondrite-normalized rare earth element (REE) plot (normalizing values
from Sun and McDonough, 1989); and (B) upper continental (UC) crust–normalized traceelement diagram (normalizing values from Taylor and McLennan, 1995) of Chichihualtepec
Tecomate Formation metasedimentary rocks.
ranging from –5.6 to +0.3 (t = 288 Ma) and depleted mantle model ages (TDM) between 1.07
and 1.35 Ga. These data represent the weighted
average of Sm-Nd isotopic compositions for
all the detrital contributions from the source
area (Arndt and Goldstein, 1987; Murphy and
Nance, 2002). The εNd (t) evolution lines of the
Chichihualtepec Tecomate Formation rocks
lie between, and partially intersect, the Sm-Nd
envelopes of both the Oaxacan Complex rocks
and the Totoltepec pluton, suggesting components of both these sources in the clastic rocks.
This interpretation is consistent with detrital
zircon geochronological data, which indicate
that the Oaxacan Complex and the regional
1622
Carboniferous–Permian arc are the two main
contributing source areas. In contrast to the data
presented herein, the Tecomate Formation in the
type area (Yañez et al., 1991) lacks a contribution from the regional Carboniferous–Permian
arc, as their εNd (t) values closely correspond
with the Sm-Nd isotopic composition of the
Oaxacan Complex (Fig. 11A). This inference
is supported by U-Pb geochronological data
of metasedimentary rocks from the Tecomate
type area (Sánchez-Zavala et al., 2004), which
yielded detrital zircon populations of Ordovician and Mesoproterozoic age.
Upper continental crust–normalized traceelement patterns of the Chichihualtepec
Along-Arc Variation
Whereas Torres et al. (1999) advocated the
presence of a Permian–Triassic arc, the ca.
306 Ma age and the arc geochemistry of the
gabbroic component of the Totoltepec pluton
provide firm evidence of magmatic arc activity
in the Pennsylvanian. Other igneous rocks of
a similar age in the southern part of the North
American Cordillera (Fig. 2) include the Cuananá plutonic complex (Vega-Carrillo et al.,
1998), which yielded a SHRIMP U-Pb age of
307 ± 2 Ma (Elías Herrera et al., 2005), and ca.
313–318 Ma granitic to dioritic intrusions in the
Altos Cuchumatanes, Guatemala (Solari et al.,
2010). Further north, the Aserradero rhyolite in
the Sierra Madre terrane yielded a U-Pb TIMS
age of 334 ± 39 Ma (Stewart et al., 1999), and
in the Coahuila terrane, the La Pezuña rhyolite
was dated at 331 ± 4 Ma (Lopez et al., 1996).
However, due to the lack of geochemical data,
an arc association of these Carboniferous rocks
can only be substantiated for the Totoltepec pluton and the Altos Cuchumatanes granitoids.
The overall spatial, geochemical, and isotopic
similarity of the ca. 289 Ma main body of the
Totoltepec pluton with the precursor 306 Ma
gabbroic rocks suggests that regional arc activity continued into the Early Permian. Other
evidence for Early Permian arc magmatism in
southern Mexico (Figs. 2 and 14) includes the
270 ± 3 Ma Cozahuico granite (Elías-Herrera
and Ortega-Gutiérrez, 2002; Elías-Herrera et al.,
2005), the 275 ± 4 Ma La Carbonera stock (Solari
et al., 2001), a 272 ± 10 Ma tonalitic gneiss in
the Xolapa Complex (Ducea et al., 2004), and
an arc-related orthogneiss in the Chiapas Massif that yielded a U-Pb SHRIMP age of 272 ±
3 Ma (Weber et al., 2007). Arc-related ca. 270–
280 Ma granitoid plutons intruding Caborca terrane basement in northwestern Mexico (Arvizu
et al., 2009; Riggs et al., 2009, 2010) indicate
that Early Permian arc magmatism extended
into the North American craton.
Arc magmatism in southern Mexico is likely to
have continued into the Middle to Early Permian,
as suggested by an arc-related orthogneiss of
258 ± 2 Ma age in the Chiapas Massif (Weber
et al., 2005) and by a crystallization age of 254 ±
7 Ma for the Mixtequita stock in the Maya terrane (Murillo-Muñeton, 1994). The northern
extension of the Early to Middle Permian con-
Mixteca
tinental arc into terranes of the North American craton is represented by ca. 258 Ma to ca.
266 Ma arc-related granites and granodiorites in
the Sierra Pinta (Arvizu et al., 2009).
This fragmentary record of late Paleozoic arc
magmatism is in broad agreement with a number of Permian K-Ar and Rb-Sr ages of igneous rocks in Mexico (Fig. 2; Ruiz-Castellanos,
1979; Damon et al., 1981; Torres et al., 1999;
Grajales-Nishimura et al., 1999).
The Chichihualtepec Tecomate Formation
strata, containing interstratified arc-derived volcanic and clastic rocks, provide complementary
data on the nature of the late Paleozoic evolution of the shallow crust. Much of the Chichihualtepec Tecomate Formation was deposited
before the Totoltepec pluton was exposed. Detrital zircon, geochemical and Sm-Nd isotopic
data, together with the presence of plutoniclastic
conglomerate, indicate that the Chichihualtepec
Tecomate Formation was largely derived from a
regional arc. The local abundance of thin granitoid dikes and very fine-grained, green, tuffaceous strata in the Chichihualtepec Tecomate
Formation suggests that arc activity was contemporaneous with Chichihualtepec Tecomate
Oaxaquia
Maya
Mixtequita
251
Sierra
Madre
Formation deposition. Evidence of arc activity
in southern Mexico (Figs. 2 and 14) may also
be preserved in (1) the latest Pennsylvanian to
Middle Permian Tecomate Formation type area,
which contains mafic flows, tuffs, and rare felsic units (Keppie et al., 2004b; Sánchez-Zavala,
2008), (2) the Middle Permian Los Hornos Formation (Ramírez et al., 2000; Vachard et al.,
2004), and (3) the uppermost Devonian to
Lower Permian Patlanoaya Group, which contains intercalations of bentonite horizons representing ash-fall deposits (Vachard et al., 2000;
Vachard and de Dios, 2002). The undeformed
Olinalá Formation of Middle to Upper Permian
age (Buitrón et al., 2005) is potentially also
partially correlative with the Chichihualtepec
Tecomate Formation strata, although volcanic
rocks have not been described in this unit. Further north, the magmatic arc is characterized by
(1) the Early to Middle Permian Tuzancoa Formation (Sierra Madre terrane), which contains
andesitic to basaltic lava flows and felsic tuffs
(Rosales-Lagarde et al., 2005), (2) the Early
Permian bentonite-bearing Guacamaya Formation in the Sierra Madre terrane (Gursky and
Michalzik, 1989), (3) the late Mississippian to
Coahuila
Xolapa
Chihuahua Caborca
Chiapas
Massif
orthogneiss
La Carbonera
Chiapas
Massif
orthogneiss
299
PENNSYLVANIAN
318
MISSISSIPPIAN
Tecomate Fm./ CTF
E
Tonalitic
gneiss
Sierra Pinta
Los Tanques
Cuanana
Patlanoaya Group
Totoltepec
271
Sonoyta
Rara Fm.
Cozahuico
Las Delicias Fm.
M
Guacamaya Fm. Tuzancoa Fm.
260
Totoltepec
CARBONIFEROUS
Age (Ma)
PERMIAN
L
Altos
Cuchumatanes
Aserradero
La Pezuña
Igneous arc-related rocks
dated by U-Pb geochronology
Sedimentary arc-assemblages
containing intercalated arcrelated volcanic rocks
359
Figure 14. Correlation chart of various arc-related igneous and sedimentary suites of Carboniferous to Permian age sorted according to
their location in the various tectonostratigraphic terranes of Mexico. For references see text.
1623
Kirsch et al.
Middle Permian Las Delicias Formation in the
Coahuila terrane (McKee et al., 1999), which
contains interstratified rhyolites, and (4) the
Early Permian, bentonite-bearing Rara Formation of the Sierra del Cuervo in the southern extension of the North American craton (Handschy
and Dyer, 1987).
As one of the samples from near the stratigraphic base of the Chichihualtepec Tecomate
Formation does not contain any Carboniferous–
Permian zircons, this regional magmatic arc
in southern Mexico is inferred to have started
developing during Chichihualtepec Tecomate
Formation deposition (Figs. 15A and 15B). The
Totoltepec pluton did not become a source for
the Chichihualtepec Tecomate Formation until
ca. 275 Ma, by which time a significant amount
of the arc crust had been removed to expose the
pluton (Fig. 15C). Although the population peak
of the late Paleozoic detrital zircon record of the
Chichihualtepec Tecomate Formation occurs at
an age of ca. 307 Ma (Fig. 6), the detrital zircon record extends back to ca. 344 Ma without
any significant gaps, suggesting that regional
magmatic arc activity may have initiated in the
Mississippian.
Taken together, the data suggest that arc magmatism had commenced in some of the southern
to central Mexican continental blocks by Mississippian times, whereas it probably did not
become established in the Laurentian (northern)
part of Mexico until the Early Permian (Fig. 14).
Across-Arc Variation
There are subtle differences in the geochemical and isotopic compositions between the
various magmatic arc suites of southern Mexico
and Guatemala. For rocks with the same SiO2
content, the Totoltepec pluton exhibits lower
HFSE (Nb, Ta, LREEs, Zr) and LILE (Rb, Th,
K) abundances and more radiogenic Sm-Nd isotopic compositions relative to the intermediate
to felsic suites in both Oaxaquia and the Maya
block, which also contain evidence of substantial crustal contamination. As certain southern
Mexican arc suites of different age show similar geochemical characteristics and certain arc
suites of roughly the same age show different
geochemical characteristics, the compositional
differences cannot be ascribed to temporal
variations in arc magmatism. Instead, observed
contrasts in composition between the individual
arc suites considered in this paper are attributed
to spatial intra-arc variation.
In general, arc rock compositions vary both
in time and with distance from the active trench,
reflecting increasing degrees of AFC as magmas pass through thicker crust, and a change
from subduction-enriched to within-plate man-
1624
sea level
OAX
MX
MAYA
pa
A
Pre-arc
ca. 330 Ma (?)
ctf/
tf
Tt—Totoltepec
Cz—Cozahuico
Cu—Cuananá
Ca—La Carbonera
Tz—Tuzancoa
Ch—Chiapas Massif
Ac—Altos Cuchumatanes
ctf/tf—Chichihualtepec
Tecomate/ Tecomate
pa—Patlanoaya
gu/dm—Guacamaya/
Del Monte
50 km
?
sea level
exposed
basement
Arc
development
ca. 300 Ma
pa
ctf/
tf
B
++
++
++
++
++
++
+
Cu
Tt
MX—Mixteca terrane
OAX—Oaxaquia terrane
MAYA—Maya block
Ac
?
++
+
Plutons
v
vv
Lava flow
Fault
Fault, inferred
sea level
gu/dm
Late arc:
Tt exhumation
ca. 270 Ma
pa
v
vv
ctf/
tf
C
++
+
++
+
+
Tt
Tz
Cu
++
+
+
++
+
Cz
++
+
Ch
Ca
Sediment
transport
Basement
Arc crust
Ac
++
+
?
Figure 15. Generalized sections across the active western margin of Pangea in the late Paleozoic, showing arc development and the relative locations of the various magmatic arc assemblages in southern Mexico and Guatemala.
tle sources (e.g., Brown et al., 1984). Typical
transverse geochemical variations include a
systematic increase in LILEs, HFSEs, and alkalis and a decrease in LILE/HFSE ratios and
εNd values from the front to the rear of the arc
(Kimura et al., 2010, and references therein).
Hence, in order to account for the more juvenile
composition of the Totoltepec pluton in comparison to other Carboniferous–Permian arc
suites in Mexico and Guatemala, the Totoltepec
pluton is inferred to have been emplaced into
a more primitive, less mature location within
the Carboniferous–Permian arc. In this model,
the pluton would constitute a more trenchward
part of the arc, lying to the west (modern coordinates) of the more mature arc suites inferred
to represent a more inboard location (Figs. 15B
and 15C). Assuming that the southern Mexican
crustal blocks, in which the Mixteca terrane occupies the western, most outboard position relative to Oaxaquia and the Maya block (Fig. 1A),
were only involved in lateral translation relative
to each other along transcurrent faults trending along strike of the arc (e.g., Dickinson and
Lawton, 2001), the position of the Totoltepec
pluton relative to the other southern Mexican
arc suites should not have changed substantially
since the late Paleozoic. Hence, the increased
arc maturity is consistent with models that advocate an eastward polarity of subduction (e.g.,
Centeno-García, 2005; Keppie et al., 2008a).
An alternative (but not necessarily mutually
exclusive) model to explain the geochemical
differences between the Totoltepec pluton and
contemporaneous arc-related plutonic rocks in
southern Mexico involves the emplacement of
the Totoltepec pluton along a fault in the arc
that facilitated its ascent and made it less prone
to contamination. This model is consistent
with transtensional kinematics associated with
strike-slip faulting documented in Chichihualtepec Tecomate Formation metaconglomerates
(Morales-Gámez et al., 2009) and evidence for
the syntectonic emplacement of the Totoltepec
pluton (Kirsch et al., 2012).
Pangea Implications
Late Carboniferous continental collision in
Mexico was a key event in the amalgamation of
Pangea and is expressed by a southerly source
for flysch deposits in the Ouachitan orogeny in
the Mississippian (Arbenz, 1989) and by the appearance of early Mississippian fossils in Oaxaquia with Midcontinent (U.S.) faunal affinities
(Navarro-Santillán et al., 2002). Because Carboniferous to Permian continental arc magmatism recorded by the Totoltepec pluton, the
Chichihualtepec Tecomate Formation, and correlative rocks elsewhere in the belt postdates the
amalgamation of Pangea, a location of the Mixteca terrane adjacent to a subducting part of the
Panthalassa Ocean on the periphery of Pangea-A
seems most likely (Fig. 1A). Such a location
is preferable to models that assign the Mixteca
terrane to a position within Pangea, either off
northeastern Canada (Fig. 1C; Böhnel, 1999) or
in the Gulf of Mexico, ~2000 km inland from the
western margin of Pangea (Vega-Granillo et al.,
2009; Fig. 1B), because these locations lie too
far from any potential subducting ocean.
ACKNOWLEDGMENTS
We acknowledge the Consejo Nacional de Ciencia y Tecnología (CONACyT; Project CB-2005-1:
24894), Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (PAPIIT:
IN100108-3), and a Natural Sciences and Engineering Research Council of Canada Discovery grant
to Murphy for funds to support the field work and
geochemical and isotopic analyses. Carlos OrtegaObregón and Ofelia Pérez-Arvizu provided technical
assistance in the Laboratorio de Estudios Isotópicos,
Centro de Geociencias. Kirsch is grateful to Maria
Helbig for help in the field and with figure preparation. We thank Associate Editor Luca Ferrari, and reviewers Peter Schaaf and Bodo Weber, as well as two
anonymous reviewers, for constructive comments on
this and a previous version of the manuscript. This is
a contribution to International Geological Correlation
Project 597.
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SCIENCE EDITOR: NANCY RIGGS
ASSOCIATE EDITOR: LUCA FERRARI
MANUSCRIPT RECEIVED 23 NOVEMBER 2011
REVISED MANUSCRIPT RECEIVED 13 FEBRUARY 2012
MANUSCRIPT ACCEPTED 18 MARCH 2012
Printed in the USA
H I S T O R I A E S T R U C T U R A L D E L P L U T Ó N T O T O LT E P E C
Artículo: Kirsch, M., Keppie, J.D., Murphy, J.B., y Lee, J.K.W., Arc plutonism in a transtensional regime: the Late Palaeozoic Totoltepec pluton,
Acatlán Complex, southern Mexico: International Geology Review, en prensa, doi: 10.1080/00206814.2012.693247.
Moritz Kirsch: concepción y el diseño del estudio; trabajo de campo
el cual incluye mapeo, obtención de datos estructurales, selección de
puntos de muestreo y toma de muestras para el análisis de petrografía
y de microsonda, así como la geocronología 40 Ar/39 Ar; adquisición
de datos de microsonda; revisión de literatura; análisis y interpretación de datos; redacción del artículo.
J. Duncan Keppie: contribución a la concepción y el diseño; supervisión de las actividades de campo; participación en la interpretación de
J. Brendan Murphy: contribución a la concepción y el diseño; supervisión de las actividades de campo; participación en la interpretación de
James K.W. Lee: participación en la interpretación de datos y en la revisión del artículo sometido; encargado de las instalaciones de análisis
40 Ar/39 Ar.
33
3
International Geology Review
iFirst, 2012, 1–24
Arc plutonism in a transtensional regime: the late Palaeozoic Totoltepec pluton, Acatlán
Complex, southern Mexico
Moritz Kirscha*, J. Duncan Keppieb , J. Brendan Murphyc and James K.W. Leed
a
Centro de Geociencias, Universidad Nacional Autónoma de México, 76230 Querétaro, Mexico; b Departamento de Geología Regional,
Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México D.F., Mexico; c Department of Earth Sciences,
St. Francis Xavier University, Antigonish, NS, Canada; d Department of Geological Sciences and Geological Engineering, Queen’s
University, Kingston, ON K7L 3N6, Canada
Downloaded by [Moritz Kirsch] at 06:52 18 June 2012
(Accepted 9 May 2012)
The ENE-trending, ca. 306–287 Ma, Totoltepec pluton is part of a Carboniferous–Permian continental magmatic arc on
the western Pangaean margin. The 15 km × 5 km pluton is bounded by two N–S Permian dextral faults, an E–W thrust
to the south, and an E–W normal fault to the north. Thermobarometric data indicate that the main, ca. 289–287 Ma, part
of the pluton was emplaced at ≤20 km depth and ≥700◦ C and was exhumed to 11 km and 400◦ C in 4 ± 2 million years.
We have documented the following intrusive sequence: (1) the 306 Ma northern marginal mafic phase; (2) the 287 Ma
main trondhjemitic phase; and (3) ca. 289–283 Ma sub-vertical dikes that vary from (a) N39E, undeformed with crystal
growth perpendicular to the margins, through (b) ca. N50–73E, foliated and folded with sinistral shear indicators, to (c)
N73–140E and boudinaged. The obliquity of the boundary between the folded and stretched dikes relative to the N–S dextral
faults suggests sequential emplacement in a transtensional regime (with 20% E–W extension), followed by different degrees
of clockwise rotation passing through a shortening field accompanied by sinistral shear into an extensional field. The ca.
289–287 Ma intrusion also contains a steep ENE-striking foliation and hornblende lineations varying from sub-horizontal
to steeply plunging, probably the result of emplacement in a triclinic strain regime. We infer that magmatism ceased when
some of the dextral motion was transferred from the western to the eastern bounding fault, causing thrusting to take place
along the southern boundary of the pluton. This mechanism is also invoked for the rapid uplift and exhumation of the pluton
between ca. 287 Ma and 283 Ma. The distinctive characteristics of the Totoltepec pluton should prove useful in identifying
similar tectonic settings within continental arcs.
Keywords: emplacement; syntectonic pluton emplacement; magmatic arc; transtension; Acatlán Complex; Mexico; Pangaea
Introduction
Calc-alkaline magmatism at convergent plate margins is
commonly associated with strike–slip faulting (e.g. Fitch
1972; Jarrard 1986; Glazner 1991; Tobisch and Cruden
1995; Gibbons and Moreno 2002), which provides conduits
for magma ascent, accommodates pluton emplacement
(Tikoff and Teyssier 1992; Grocott et al. 1994; Grocott
and Taylor 2002), and facilitates the exhumation of deeper
crustal sections (Crawford et al. 1999; Žák et al. 2005).
Due to the complex interaction between thermal and structural effects of plutonism and regional-scale deformation,
the mechanisms responsible for pluton emplacement in
continental magmatic arcs have attracted much attention.
We present a case study of the mechanisms controlling the emplacement of the ca. 306–287 Ma, suprasubduction zone Totoltepec pluton in the eastern Acatlán
Complex, southern Mexico. This pluton is representative
of a Pennsylvanian to Early Permian arc assemblage
*Corresponding author. Email: [email protected]
ISSN 0020-6814 print/ISSN 1938-2839 online
© 2012 Taylor & Francis
http://dx.doi.org/10.1080/00206814.2012.693247
http://www.tandfonline.com
along the western margin of Pangaea that developed
soon after Pangaea formed (e.g. Torres et al. 1999;
Dickinson and Lawton 2001; Centeno-García 2005). A previous contribution (Kirsch et al. 2012) documented the
geochemical/isotopic characteristics and age of the pluton, and indicates that the body is a composite intrusion
with mantle and crustal sources, emplaced along an immature, trenchward part of the late Palaeozoic continental
arc. In this article, we use a combination of meso- and
microfabric analyses, Al-in-hornblende thermobarometry
and 40 Ar/39 Ar geochronology, which provide evidence for
(1) the incremental assembly of the pluton (e.g. Coleman
et al. 2004; Glazner et al. 2004; de Saint Blanquat et al.
2006; Pignotta et al. 2010), (2) sequential injection of
sheets (Miller and Paterson 2001; Mahan et al. 2003),
(3) progressive fabric development during crystallization
of the pluton in a strain field (e.g. Paterson et al. 1989,
1998; Tribe and D’Lemos 1996; Barros et al. 2001), and
2
M. Kirsch et al.
(4) intrusion in a transtensional environment (Petford and
Atherton 1992; Paterson and Fowler 1993; Hanson and
Glazner 1995; Kratinová et al. 2007). Given the pluton
location, our data also provide insights into the geodynamic evolution of the late Palaeozoic magmatic arc that
developed along the periphery of Pangaea.
Geological setting
The Totoltepec pluton is well-exposed in the eastern part
of the Palaeozoic Acatlán Complex (Figure 1A; Mixteca
terrane) and is one of several Carboniferous to Permian
intrusions associated with a continental magmatic arc
that formed as a consequence of subduction along the
palaeo-Pacific margin of Pangaea (Torres et al. 1999;
Keppie et al. 2004a; Kirsch et al. 2012). The Acatlán
Complex is tectonically bound to the south by the
Cenozoic La Venta/Chacalapa Fault (Solari et al. 2007;
Tolson 2007), juxtaposing it against the Xolapa Complex
(Figure 1A). To the west, the Acatlán Complex is thrust
over Cretaceous platformal carbonates, located between
the exposed Acatlán Complex and the accreted Guerrero
terrane (Centeno-García et al. 2008; Ramos-Arias and
Keppie 2011). To the north, the complex is unconformably overlain by Mesozoic rocks and the Cenozoic
Trans-Mexican Volcanic Belt (Ferrari et al. 1999). To the
east, the Acatlán Complex is bounded by the >150 kmlong, N–S-striking, dextral Caltepec Fault Zone (CFZ),
which separates it from the ∼1 Ga Oaxacan Complex
(Elías-Herrera and Ortega-Gutiérrez 2002). White mica
from a mylonitic mica schist in the CFZ yielded a
40 Ar/39 Ar age of ca. 269 million years (Elías-Herrera
et al. 2005). However, two syntectonic plutons – the ca.
307 Ma Cuananá plutonic complex and the ca. 270 Ma
Cozahuico granite – attest to tectonomagmatic activity
along this fault during late Pennsylvanian to Early Permian
times.
The Totoltepec pluton is approximately elliptical in
map view; its long axis (15 km) trends roughly WNW–
ENE (Figure 1B) and it crops out over an area of 68 km2
with a relief of 490 m. External contacts between the
Totoltepec pluton and the surrounding strata are either
non-conformable or tectonic (Malone et al. 2002), i.e.
none of the original contact relationships are preserved.
Along its southern margin, the Totoltepec pluton is thrust
over intensely deformed, lower greenschist-facies metasedimentary rocks of the Pennsylvanian to Middle Permian
Tecomate Formation (Keppie et al. 2004b; Kirsch et al.
2012). To the east, an unnamed, medium-grade metamorphic unit consisting of garnet schist and quartzite with rare
amphibolite dikes is faulted against the Totoltepec pluton (Kirsch et al. 2012). To the north, the granitoid body
is unconformably overlain by and faulted against redbeds
of inferred Jurassic age (Malone et al. 2002). The N–S
trending, dextral San Jerónimo fault (Morales-Gámez et al.
2009) separates the pluton from the Tecomate Formation
and Jurassic redbeds along its western margin.
Field relationships and geochronological data indicate
that the Totoltepec pluton was emplaced over a ca. 19 million year period involving at least two discrete intrusions,
i.e. (1) 306 ± 2 Ma, mafic–ultramafic intrusive bodies
of hornblende-rich gabbros and hornblendites that occur
as three minor (0.2–0.6 km2 ), elongate, fault-bounded
bodies distributed along the northern and northeastern
margin of the pluton (Kirsch et al. 2012), and (2) the
main body, making up approximately 98% of the exposed
area, dated at 287 ± 2 Ma (trondhjemite: Yañez et al.
1991), 289 ± 1 Ma (diorite: Keppie et al. 2004a), and
289 ± 2 Ma (quartz diorite: Kirsch et al. 2012), ranging in composition (in order of decreasing proportion)
from trondhjemite (hornblende-rich) tonalite, and diorite
to quartz granitoid, granodiorite, monzogranite, and rare
plagioclase-rich (cumulate?) layers.
Geochemistry of the older marginal Totoltepec mafic–
ultramafic rocks indicates an arc tholeiitic to calc-alkaline
affinity characterized by high LILE/HFSE ratios, flat REE
patterns, and initial εNd values of +1.3 to +3.3 (t =
306 Ma). The younger Totoltepec main body exhibits a
calc-alkaline trace-element geochemistry with flat to moderately fractionated LREE-enriched patterns, and initial
εNd values of –0.8 to +2.6 (t = 289 Ma; Kirsch et al.
2012). Although minor degrees of crustal assimilation and
fractionation processes are detected by simple isotopic
modelling, the isotopic data plot within the evolutionary
envelope defined by Ordovician mafic rocks of the Mixteca
terrane interpreted to have been derived from a ca. 1.0 Ga
subcontinental lithospheric mantle (Murphy et al. 2006;
Ortega-Obregón et al. 2010).
Lithological units and internal contacts
The oldest, ca. 306 Ma gabbros and minor hornblendites
occur in three fault-bounded, lenticular bodies along the
northern and northeastern margin of the pluton. These
mafic to ultramafic rocks are massive to weakly foliated
and, in places, possess a compositional banding. Locally,
they are intruded by steep, <1 m-wide, intensely deformed,
locally disrupted felsic dikes (Figure 2A) of inferred
289–287 Ma age (Kirsch et al. 2012). The ca. 289–287 Ma
rocks from the main body of the pluton have two modes
of occurrence: (1) hornblende-bearing mafic to intermediate rocks, which occur as sheets consisting of compositionally banded, foliated, locally mylonitic, fine grained
to megacrystic hornblende diorite, quartz diorite, and
tonalite and (2) felsic rocks, forming the interior and
largest proportion of the Totoltepec pluton, chiefly composed of equigranular, weakly to moderately foliated
trondhjemite.
The mafic–intermediate sheeted domain occurs as
smaller bodies along the southern margin of the pluton
-99°
-98°
-97°
-96°
Puebla
st
Fig. B
th
ru
Tehuacán
p an
A
Y
A
Pa
C al te p e c f a u l t
pa
lu
tl a
Te l o l o a
ru
M
th
Acatlán
de Osorio
st
Oa x
J
fau
U
lt
U/Pb and
Ar/Ar ages
Microprobe sampling pts.
A
Oaxaca
32
34
Oaxacan Complex
O
ha
LE
X
ca
la p
72
A X
A Q U I A
af
au l
t
86
42
o Fault
San Jerónim
74
TT-17
39
67
41
TT-28
72
33
41
63
74
68
75
81
27
54
69
45
54
77
89
79
81
86
86
Tonahuixtla fault block
45
71
81
80
78
54
69
44
289 ± 2
75
55
San Jerónimo de Xayacatlán 43
40
TT-54
37
65
88
76
77
X’
TT-55
77
54
TT-13a
36
TT-14
48
63
37
64
50
60
289 ± 1
70
89
52
287 ± 2
41
86
55
283 ± 1
72
80
28
Santo Domingo Tonahuixtla
78
76
63
88
26
14
56
90
71
B
59
25
59
52
82
76
89
85
Fig. 3
40
50
61
57
0
0.5
1
86
18°12'0"N
86
18°14'0"N
90
2
km
Scale 1:65,000
63
97°54'0"W
97°52'0"W
97°50'0"W
97°48'0"W
2x vertical exaggeration
1500
Elevation
(m)
84
67
306 ± 2
z
Matan
57
54
29 55
68
73
78
a fault
16
68
37
X
18°16'0"N
A
Puerto
Escondido
65
5
lt
fa u
9
Acatlán Complex
Trans-Mexican Volcanic Belt
go
te n
uis
MP
C
CO
ng
Tia
PA
Z
LA
f a ul t
Cretaceous
Jurassic
Chichihualtepec
Tecomate Fm.
Unnamed Unit
Salada Unit
Granodiorite, monzo-granite
Trondhjemite
Diorite, tonalite (sheeted domain)
Hornblende gabbro, hornblendite
E
XO
Acapulco
osa
R
L a Ve n t a f a u l t
18°
ta H
erm
aca
M I X T E C A
V is
Cities
Highways
Roads
Rivers
Totoltepec pluton
Foliation
Lineation
Contact
Contact, inferred
Strike–slip fault
Normal fault
Thrust fault
19°
75 km
GUERRERO
MORELOS
PLATFORM
3
1000
C
0
?
?
X
500
1000
1500
2000
2500
3000
3500
4000
?
4500
X’
5000
5500
6000
Figure 1. (A) Location of the study area (box) with respect to the principal geologic features of southern Mexico (modified from Keppie
et al. 2008). (B) Simplified geological map and (C) interpretative cross section of the Totoltepec pluton and surrounding country rocks.
Short, heavy dashes represent locations of measured foliations; crosses are interpreted foliation patterns.
and in a larger, margin-parallel, lenticular, sigmoidal zone
(Figures 1B and 3). These zones are composed of steeply
dipping to sub-vertical, aplitic to coarse-grained sheets,
or dikes of centimetre to several tens(?) of metres width
displaying variable degrees of pinch-and-swell undulations (Figure 2D). Locally, dikes occur as swarms of
4
M. Kirsch et al.
(A)
(B)
(C)
(D)
(F)
(I)
(E)
(G)
(J)
(H)
(K)
Figure 2. Diking in the Totoltepec pluton. (A) Disaggregated felsic dike in marginal hornblende gabbro. (B) Swarm of parallel, narrow,
interconnected mafic dikes that locally display tapering terminations. (C) Boudinaged composite dike with a felsic interior and a mafic
margin. (D) Sequence of pinching and swelling dikes composing the mafic–intermediate sheeted domain in the southern part of the
pluton. (E) Gently folded pegmatite dike, and (F) fabric-discordant late felsic dike in the sheeted zone. (G) Close-up of Figure 2E,
showing elongate, sigmoidal quartz grains growing perpendicular to the dike margin. (H) Sigmoidal internal fabric of a felsic dike in
the mafic–intermediate sheeted zone. (I) Deflection of amphibole into the plane of cross-cutting dikes. (J) Aplitic dike cross-cutting the
fabric of megacrystic diorite. Note the dike-internal foliation parallel to the dike margin. (K) Trondhjemite dike in the felsic interior of the
pluton.
many parallel, narrow (2–15 cm wide), steep, anastomosing sheets that locally show tapering terminations
(Figure 2B), or as 10–15 cm-wide composite dikes with a
felsic, pegmatitic interior and a mafic margin (Figure 2C).
Dikes of trondhjemitic or quartz-rich granitoid composition, which are inferred to be co-magmatic with the
felsic pluton interior based on matching petrographic and
geochemical characteristics (Kirsch et al. 2012), intrude
the mafic–intermediate sheeted domain and are commonly
laterally traceable for several metres along strike. These
felsic dikes are generally steep and either (1) fabricdiscordant, around 10 cm wide, and undeformed to gently folded (Figures 2E and 2F) or (2) fabric-concordant,
5–40 cm wide, and exhibiting pinch-and-swell as well as
boudinage structures (e.g. Figure 3D). The felsic dikes vary
from fine grained to pegmatitic. The transition between
the mafic–intermediate sheeted zone and the more felsic
pluton interior is characterized by the gradual decrease in
the occurrence of mafic dikes.
Compared with the mafic–intermediate sheeted
domain, the felsic interior part of the pluton is compositionally and texturally more homogeneous. In certain
locations, however, the felsic interior exhibits elevated
modal plagioclase or biotite, with subordinate granodiorite
and monzogranite occurring near the northern boundary
of the pluton. Moreover, although less conspicuous due
to their compositional similarity, felsic dikes intrude
trondhjemite in the main body of the pluton (Figure 2K).
Enclaves in the Totoltepec pluton are very rare
and heterogeneously distributed (Figure 4). In the
mafic–intermediate sheeted domain, these include
centimetre- to decimetre-sized, rounded to elongate,
foliated microgranular enclaves (autoliths) of dioritic
composition (Figure 4A), whose contacts with the igneous
host are defined by chilled margins or dark, hornblenderich reaction rims (Figure 4B). Elongate enclaves are
commonly oriented parallel to the foliation in the host
rock (Figure 4C). Locally, within the mafic–intermediate
sheeted domain, 5–15 cm-long, partly disaggregated clots
of hornblende can be observed (Figure 4D). The interior
felsic domain locally contains (1) isolated, centimetresized, ovoid globules made up of coarse-grained biotite
(Figure 4E) and (2) strongly sheared, fault-bounded microdioritic enclaves of 25 cm length (Figure 4F). No xenoliths
derived from the surrounding country rocks have been
recognized in the Totoltepec pluton, consistent with the
absence of xenocrystic zircons (Kirsch et al. 2012).
Locally within the mafic–intermediate sheeted domain,
a steeply dipping textural and compositional banding is
developed, made up of alternating coarse-grained and finegrained bands that coincide with subtle differences in
the relative proportions of hornblende and plagioclase.
This banding is most conspicuous in an outcrop east of
Santo Domingo Tonahuixtla (Figures 1B and 3), where
individual layers are continuous for several metres along
strike. In diorite, the banding is irregularly spaced, consisting of a few millimetres to about 1.5 cm-wide leucocratic
and relatively coarse-grained bands, and approximately
0.5–3.5 cm, locally bifurcating, dark (fine-grained) bands
(Figure 3H). In tonalite, dark and light bands have a similar average width of about 3 cm (Figure 3I). In both
lithologies, light bands exhibit a porphyritic grain-size
5
distribution, containing hornblende (diorite) or plagioclase
(tonalite) phenocrysts of up to 0.5–1 cm length in a finegrained matrix. Dark bands are composed of small grains
with roughly equal grain size. The transition between light
and dark layers is generally sharp and the rocks tend to
split along this anisotropy plane. Locally, within banded
tonalite, however, plagioclase phenocrysts are observed
to grow across the boundaries between fine-grained and
coarse-grained domains.
Petrography
The ca. 306 Ma marginal mafic–ultramafic bodies of the
Totoltepec pluton are dominated by hornblende gabbro,
with averages of 53% modal plagioclase (labradorite), 37%
amphibole, and 10% other phases including magnetite,
ilmenite, chalcopyrite, muscovite, titanite, and zircon, as
well as secondary minerals epidote, chlorite, sericite, and
antigorite. Locally, the gabbro grades into hornblendite,
which is characterized by approximately 90% modal
amphibole.
The ca. 289–287 Ma main body of the pluton predominantly consists of trondhjemite, whose average modal
composition is 54% plagioclase (oligoclase), 35% quartz,
and 11% other constituents, including primary muscovite,
biotite, apatite, magnetite, titaniferous magnetite, ilmenite,
and zircon, as well as rare K-feldspar and titanite.
Secondary minerals include albite (after oligoclase),
sericite, chlorite, epidote, antigorite, haematite, and
calcite. Mafic–intermediate rocks in the southern part
of the pluton are composed of hornblende-rich tonalite
(32% andesine, 38% amphibole, 23% quartz, and 7%
of other phases), hornblende-rich diorite (40% andesine,
53% amphibole, and 7% other), and quartz-diorite (80%
andesine, 15% quartz, and 5% other). Rare leucocratic
felsic dikes (see above) intruding this mafic–intermediate
domain have a composition corresponding to either
trondhjemite or quartz-rich granitoid (68% quartz, 30%
albite, and 2% other). East of the town of Totoltepec de
Guerrero (Figure 1B), plagioclase-rich rocks (93% albite,
3% quartz, and 4% other) and biotite trondhjemite (55%
oligoclase, 35% quartz, 7% biotite, and 3% other) are
the predominant lithologies. Towards the northern margin
of the pluton, the felsic rocks locally contain abundant
potassium feldspar (up to 40%) and are classified as granodiorite and monzogranite according to the nomenclature
of Streckeisen (1976).
Plagioclase is the predominant mineral of the
Totoltepec pluton, occurring as subhedral to euhedral
grains varying in size from 2 mm to 6 mm. Depending
on lithology, plagioclase varies in composition from albite,
through oligoclase to labradorite. In tonalite, diorite, and
gabbro, plagioclase exhibits normal compositional zoning
(Table DR-1; see supplementary material at http://dx.doi.
org/10.1080/00206814.2012.693247). Biotite occurs as
isolated, tabular grains or as inclusions in plagioclase.
6
M. Kirsch et al.
(A)
(B)
(E)
(F)
(C)
(D)
(G)
( H)
(I)
15 cm
SZB
D.
A.
F.
C’ plane
S plane
25 cm
2 cm
20 cm
78
E.
81
C.
B.
61
10 cm
54
49
3 cm
1 cm
Totoltepec
de Guerrero
55
43
59
39
32
37
60
59
50
47
49
55
36
41
61
65
54
70
77
81
38
64
75
G.
36
71
81
28
72
3 cm
28
20
H.
Santo Domingo
Tonahuíxtla
78
25
3 cm
26
Mafic dikes
Megacrystic
hornblende
33
0
63
59
0.5
14
1 km
I.
3 cm
Figure 3. Subset of Figure 1B showing detailed structural information as well as photographs and pictograms of the most intriguing
structures within the high-strain zone in the southern part of the Totoltepec pluton. Stereograms show foliations and dike orientation
plotted as great circles (continuous and dashed lines, respectively), lineations as filled triangles (+ shear sense if kinematic indicators
found). (A) C’ type shear band fabric indicating sinistral shear. Angle between shear band cleavage and shear zone boundary (SBZ) is
15–35◦ (Blenkinsop and Treloar 1995). (B) Sigma-type hornblende porphyroclasts indicating sinistral kinematics. (C) Randomly oriented
hornblende on the foliation plane. (D) Foliation-parallel shearband boudins of a felsic dike indicating left-lateral shear. (E) Curvature
of foliation indicating sinistral shear. (F) Lens-shaped boudins of a mafic dike with sinistral kinematics. (G) Strong mineral lineation in
megacrystic hornblende diorite indicating top-to-SSE thrusting. (H–I) Compositional/textural banding in hornblende diorite and tonalite
defined by variation in grain size and modal proportions of feldspar and hornblende. Note the growth of plagioclase phenocrysts across
layer boundaries in Figure 3I.
(A)
(B)
(C)
(D)
(E)
7
(F)
Figure 4. Magmatic enclaves in the Totoltepec pluton. (A) Foliated, rounded microgranular enclaves in hornblende diorite. (B)
Hornblende-rich reaction rim marking the contact between a microgranular enclave and diorite host. (C) Elongate microgranular enclave
aligned parallel to foliation of host diorite. (D) Disaggregated clot of hornblende in diorite. (E) Ovoid biotite globule in trondhjemite. (F)
Strongly sheared, fault-bounded microdioritic enclave in trondhjemite.
Amphibole is by far the most abundant mafic mineral in the Totoltepec pluton. It occurs as subhedral
to euhedral, prismatic grains, 1–3 mm in length, and
locally as megacrysts up to 4 cm in length. It commonly exhibits simple {100} twinning and commonly
contains inclusion of quartz, plagioclase, apatite, and titanite. In some thin sections, amphibole occurs as coarse,
lath-shaped oikocrysts poikilitically enclosing euhedral
plagioclase or subhedral to euhedral, oriented quartz
grains. In tonalite, quartz diorite, hornblende gabbro, and
8
M. Kirsch et al.
(A) 1.0
Magnesiohornblende
Tschermakitic
hornblende
Mg/(Mg+Fe 2+)
0.9
0.8
Tschermakite
0.7
0.6
0.5
Ferrotschermakitic
hornblende
Ferrohornblende
0.4
7.0
6.8
6.6
6.4
Ferrotschermakite
6.2
6.0
5.8
Si (pfu)
(B)
Main
body
(Na+K)A
Paragasitic
hornblende
Paragasite
0.4
Hornblende
0.2
Tschermakite
Tschermakitic
hornblende
0
7.0
6.9
6.8
6.7
6.6
6.5
6.4
6.3
6.2
6.1
6.0
Si (pfu)
2.0
(C)
Gln
Trm, Ts
Brs
1.5
AlVI p.f.u.
Marginal
TT-13a,Tonalite (intermediate)
TT-55, Tonalite (mafic)
TT-54, Tonalite (mafic)
TT-14, Qtz Diorite (mafic)
TT-17, Hbl Gabbro (mafic)
TT-28, Hornblendite (ultramafic)
1.0
Prg
Wnc, Eck
Ktp
0.5
Ed
Tr, Rct
0
0
0.5
1.0
1.5
2.0
AlIV (pfu)
Figure 5. Electron microprobe major-element data for amphiboles from the Totoltepec pluton (grey symbols – cores; black symbols –
rims). (A) Mg/(Mg + Fe2+ ) vs. Si classification after Leake (1978) and Leake et al. (1997, 2004). (B) Plot of A-site occupancy against Si.
Nomenclature after Leake (1978). (C) Six-fold Al plotted against 4-fold Al. Al determined according to the calculation scheme of Leake
(1978) and Leake et al. (2004). Solid black line denotes slope of 1. Locations for different amphibole end-member compositions are from
Laird and Albee (1981). Mineral abbreviations after Whitney and Evans (2010).
hornblendite, amphiboles are calcic (i.e. have (Ca + Na)B
≥ 1.00 and NaB < 0.50 atoms per formula unit) (Leake
et al. 2003; Table DR-2; see supplementary material at
http://dx.doi.org/10.1080/00206814.2012.693247). On the
Mg/(Mg + Fe2+ ) vs. Si classification diagram (Figure 5A),
they range from (ferrian- to ferri-) tschermakite to
tschermakitic hornblende and magnesio-hornblende in
composition. A few amphiboles in the tonalite and hornblendite have (Na + K)A ≥ 0.50, corresponding to hastingsite to magnesio-hastingsite. On the (Na + K)A vs.
Si classification diagram (Figure 5B), the samples fall in
the field of hornblende, tschermakitic hornblende, pargasitic hornblende, and tschermakite. Aluminium preferentially resides in the tetrahedral position (Figure 5C),
which suggests the dominance of high-T edenite-type
((Na, K)A AlIV = [ ]A Si) substitution. Si in all investigated amphiboles varies between 6.0 and 6.8. These overall
compositional characteristics are typical of igneous amphiboles (Leake 1971; Leake et al. 2003). Although optically
continuous, most investigated amphiboles are zoned, and
most cores contain higher AlIV and (Na + K)A and lower
Si and Mg/(Mg + Fe2+ ) than rims.
Quartz generally occurs as interstitial, anhedral aggregates of variable grain size. The shapes of individual quartz
clusters range from subspherical to lenticular. In places,
quartz is present as hexagonal, equigranular, polygonized
grains. It is also found as a vermicular intergrowth in
plagioclase (myrmekite).
Biotite occurs as small euhedral inclusions in plagioclase and more rarely as subhedral grains in the matrix.
It is generally, partially, or entirely replaced by chlorite.
In the area east of Totoltepec de Guerrero (Figure 1B),
modal biotite is as high as 7%. Muscovite is ubiquitous
in trondhjemite, occurring as large, discrete grains up to
1.5 mm wide or as foliated aggregates wrapping around
hornblende or plagioclase phenocrysts. Si contents of
investigated muscovite grains reach values of 3.17 per
formula unit (Table DR-3; see supplementary material
at http://dx.doi.org/10.1080/00206814.2012.693247), indicating the presence of a minor phengitic component (e.g.
Massonne and Schreyer 1987).
Potassium feldspar occurs as rare interstitial, fine- to
medium-grained crystals of microcline. In granodiorite and
monzogranite near the northern margin, orthoclase forms
subhedral phenocrysts up to 3 mm in diameter containing
flame-shaped albite lamellae.
Opaque phases include (titaniferous) magnetite,
ilmenite, and minor secondary pyrite and chalcopyrite
(Table DR-4; see supplementary material at http://dx.doi.
org/10.1080/00206814.2012.693247). Magnetite is spatially related to the main mafic minerals. It is dominantly
subhedral or euhedral with a diameter of up to 0.5 mm,
containing lamellae of ilmenite, which are interpreted as
oxidation–exsolution intergrowths. Two diorite samples
from the main body of the pluton contain ovoid interstitial
intergrowths of ilmenite with euhedral apatite. Ilmenite
is also observed to form broad lamellae in sandwich-like
intergrowths with an impure Ti-Fe-Al bearing silicate
phase.
Meso- and microstructures
Marginal, ultramafic–mafic plutonic phase (ca. 306 Ma)
Mesoscopic structures in the older, ultramafic–mafic rocks
of the pluton are preserved in one of the gabbroic
9
bodies along the northern margin. Here, a weak magmatic
foliation, defined by the preferred orientation of prismatic
to tabular amphibole, is steeply dipping to sub-vertical and
appears to be folded about a steeply, westerly plunging
fold axis (Figure 6F). An associated moderately plunging to sub-horizontal mineral lineation is locally defined
by the alignment of sub- to euhedral, elongate amphibole.
Dike orientations in this part of the marginal plutonic phase
are highly variable and can be explained by folding about
an axis that coincides with the fold axis derived from the
foliation plane distribution. This suggests that the foliation
and the dikes had similar pre-folding orientations.
Microstructures in the older, marginal phase of the
Totoltepec pluton record magmatic through incipient solidstate deformation at high temperature. Magmatic textures
are typified by large, euhedral to subhedral, unstrained,
and evenly distributed amphibole and plagioclase set in
a feldspathic matrix that lacks evidence of plastic deformation. Plagioclase has a typically igneous composition
(An54–57 ; Table DR-1) and is characterized by a normal growth zoning. The amphibole also has an igneous
composition (Figure 5) and occurs as independent, stubby
to lath-shaped crystals (Figure 7A) or as undeformed
poikilitic grains around plagioclase. Some thin sections
from two of the ultramafic–mafic bodies at the northeastern margin (Figure 8) contain textures indicative of
minor subsolidus deformation at high temperature, such
as (1) albite twins within plagioclase sub-grains that are
misoriented with respect to the host grain (Figure 7E), suggesting progressive sub-grain rotation recrystallization that
occurred at temperatures above upper greenschist-facies
conditions (Fitz Gerald and Stünitz 1993; Rosenberg and
Stünitz 2003), and (2) evidence of myrmekite replacement
at plagioclase grain peripheries, which has been interpreted
to reflect deformation temperatures in excess of 500◦ C
(Menegon et al. 2006, and references therein).
Main, mafic–felsic plutonic phase (ca. 289–287 Ma)
The main body of the Totoltepec pluton contains a
mesoscopic foliation and lineation of variable intensity,
which formed under a variety of temperature conditions.
Foliations that are interpreted to reflect deformation in
the magmatic state or in a high-temperature solid state
are defined by the preferred orientation of elongate,
undeformed, magmatic amphibole in mafic–intermediate
lithologies. Commonly, amphibole is randomly distributed
on the foliation plane (Figure 3C). Locally, however, a
sub-horizontal to sub-vertical lineation is defined by the
alignment of sub- to euhedral amphibole laths within the
foliation plane. In the more leucocratic rocks, deformation at magmatic to high-temperature, solid-state conditions is indicated by sub- to euhedral plagioclase and
interstitial quartz that define a weak planar grain-shape
preferred orientation as well as a poorly developed
10
M. Kirsch et al.
High-temperature
solid-state domain
(B)
Magmatic domain
MAIN BODY
(A)
n(S) = 174
n(L) = 34
Low-temperature
solid-state domain
Moderate-temperature
solid-state domain
Poles to foliation
Mineral lineation
(C)
n(S) = 51
n(L) = 13
(D)
n(S) = 26
n(L) = 8
39°
Dikes
Calculated
fold axis
Undeformed/folded
(E)
Extended/boudinaged
Unclassified
n = 58
(F)
n(S) = 8
n(L) = 3
n(D) = 6
MARGINAL BODIES
73°
Simple
shear
Dike orientations
Foliation
sion Transpre s
nst en
sio
Tr a
n(S) = 13
n(L) = 1
Figure 6. Mesoscopic structural data from the Totoltepec pluton. (A–D) Foliation and lineation data for the magmatic as well as hightemperature, moderate-temperature, and low-temperature solid-state domains in the main body of the pluton. (E) Lower hemisphere, equal
angle projection of dike orientations in the main phase of the pluton. 39◦ corresponds to the minimum clockwise (interpreted as initial)
dike angle; 78◦ marks the clockwise angle of transition between folded dikes, and dikes that show pinch-and-swell and/or boudinage.
Grey lines and arrows indicate the theoretical transitions between the field of finite shortening, and the field of finite shortening followed
by extension based on forward modelling along a vertical, dextral N–S-striking shear zone boundary (modified after Kuiper and Jiang
(2010)). See text for details. (F) Orientation of structural elements in the marginal mafic–ultramafic bodies of the Totoltepec pluton. All
stereograms (except Figure 6E) are equal-area, lower-hemisphere projections. Contours were drawn according to the method of Kamb
(1959) using a 3σ significance level and a 2σ contour interval.
(B)
(A)
(C)
0.1 mm
0.25 mm
0.75 mm
(D)
11
(F)
(E)
(D)
0.75 mm
0.25 mm
(G)
(I)
(H)
0.1 mm
0.25 mm
0.75 mm
0.75 mm
Figure 7. Photomicrographs of characteristic textures in the magmatic domain (m), as well as high-T (hss), medium-T (mss), and low-T
(lss) solid-state domains of the Totoltepec pluton. (A) Euhedral, randomly distributed amphibole (m). (B) Quartz with chess-board subgrain pattern (hss). (C) Rectangular, mosaic-like contours in quartz (hss). (D) Equigranular, polygonal quartz grains (hss). (E) Sub-grain
rotation in plagioclase (hss). (F) Myrmekite formation in plagioclase at the boundary with K-feldspar (hss). (G) Glide twins in plagioclase
(mss). (H) Quartz aggregate recrystallized by sub-grain rotation (mss). (I) Fractured plagioclase grain with development of new grains by
microcracking and bulging-recrystallization (lss).
1
2
3
4
5 km
Magmatic
High-temperature solid state
Moderate-temperature solid state
Low-temperature solid state
Figure 8. Spatial distribution of microstructural types within the Totoltepec pluton based on thin section analyses using criteria outlined
by Blumenfeld and Bouchez (1988), Paterson et al. (1989), Miller and Paterson (1994), and Büttner (1999).
12
M. Kirsch et al.
lineation. Locally, in the mafic–intermediate sheeted
domain, the foliation is defined by primary igneous
compositional banding (Figures 3H and 3I).
Mesoscopic fabrics of tectonic origin occur within
a high-strain zone in the southern part of the pluton
(Figure 3) and show pervasive recrystallization under subsolidus conditions. In this zone, the foliation is defined
by the preferred orientation of amphibole and plagioclase,
as well as mica. An associated linear fabric is defined
by the alignment of stretched amphibole and plagioclase
(Figure 3G), which show evidence of straining (both ductile
recrystallization and fracturing) in a section perpendicular
to the foliation and parallel to the lineation. The compositions of recrystallized amphibole and plagioclase are
similar to those of igneous grains.
In agreement with the range of observed mesoscopic
fabrics, the younger, main phase of the Totoltepec pluton
shows a continuum from primary igneous (i.e. pre-full
crystallization) microstructures to those corresponding to
deformation in the solid state (i.e. subsolidus). Criteria
outlined by Blumenfeld and Bouchez (1988), Paterson
et al. (1989), Miller and Paterson (1994), and Büttner
(1999) allow the distinction of four microstructural types:
(1) magmatic, (2) high-temperature (>500◦ C) solid state,
(3) moderate-temperature (450–500◦ C) solid state, and
(4) low-temperature solid state.
Magmatic microstructures in the main body of the
pluton are predominantly encountered in the northeastern part and locally within the mafic–intermediate sheeted
domain near the southern margin of the pluton (Figure 8).
They are characterized by coarse-grained plagioclase and
amphibole laths with angular outlines surrounded by
a largely isotropic matrix composed of ovoid, interstitial, optically continuous quartz, smaller grains of randomly distributed plagioclase, and decussate, undeformed
muscovite, and/or biotite. The plagioclase has a typically
igneous composition (An30–45 ; Table DR-1), shows normal
compositional zoning, and commonly displays grain aggregation (synneusis) textures. Igneous amphibole (Figure 5)
occurs as single subhedral poikilitic grains or as euhedral
inclusions in plagioclase.
The majority of samples in the main ca. 289–287 Ma
body of the pluton exhibit microstructures consistent
with high-temperature subsolidus deformation (Figure 8).
Quartz shows (1) basal and prismatic (chess-board)
sub-grain patterns (Figure 7B), indicating deformation
at temperatures of about 650–750◦ C (Mainprice et al.
1986; Kruhl 1996), (2) lobate grain boundaries typical
of recrystallization by grain boundary migration (Hirth
and Tullis 1992), (3) rectangular, mosaic-like contours
(Figure 7C), suggesting strong crystallographic control
on grain boundary orientations under high-temperature
deformation (Gapais and Barbarin 1986), and (4) a
strain-free, equigranular, polygonal texture, characteristic of recovery and recrystallization processes above
epidote-amphibolite facies conditions (Figure 7D; Simpson
1985). Plagioclase grains locally show evidence of subgrain rotation recrystallization and myrmekitic intergrowth
(Figure 7F).
Microstructural features diagnostic of moderatetemperature solid-state deformation mostly occur in samples of high-strain zones in the southern part of the
pluton (Figure 8) and include plagioclase showing a sweeping undulatory extinction, bent or tapering twin lamellae
(Figure 7G), as well as internal fracturing (Fitz Gerald
and Stünitz 1993). Locally, plagioclase is recrystallized
along its margins, forming core-and-mantle structures.
Muscovite occurs as kinked or bent grains, and as aligned
fine-grained anastomosing laths that enclose relict phenocrysts. K-feldspar exhibits abundant perthite flames
(Pryer 1993). Quartz is characterized by large relict grains
exhibiting patchy, undulose extinction passing laterally
into polycrystalline quartz aggregates with irregular grain
boundaries developed predominantly by sub-grain rotation
recrystallization (Figure 7H).
Low-temperature, solid-state microstructures in mainphase rocks of the Totoltepec pluton are also locally present
in high-strain zones near the southern margin of the pluton
(Figure 8) and are characterized by a pervasive cataclastic texture (Figure 7I). The presence of angular plagioclase
grains and a wide range of grain sizes suggest that grainsize reduction in feldspar is achieved by microcracking
and comminution (Tullis and Yund 1987). Quartz exhibits
deformation lamellae transected by bands of small, new
grains formed by bulging recrystallization (Hirth and Tullis
1992). Feldspar and amphibole are almost entirely replaced
by chlorite, sericite, epidote, and antigorite, indicating
fluid-enhanced deformation under lower greenschist-facies
conditions.
Overall, the orientations of the foliation in the main
part of the pluton vary from (1) moderately northerly dipping in the southern part of the pluton, (2) sub-vertical,
E–W striking in the centre, to (3) steeply southerly dipping in the northern part, defining a fan-like pattern in
N–S cross section (Figure 1C). There is a close agreement in the orientation of foliations over the entire range
of deformation temperatures (Figures 6A–6D). Moderateto low-temperature foliations tend to be less steeply dipping, because these occur mainly in the southern part of
the pluton.
The foliation within the mafic–intermediate, sheeted
zone is deformed into intrafolial, mesoscopic, recumbent, tight to isoclinal, predominantly S-shaped folds
(Figure 9). Regional variations in the trend of foliation
planes throughout the pluton are attributed to mapscale, open, upright, gently northerly plunging folds,
about which the southern thrust contact is also folded
(Figure 1B).
Lineations show a variation in orientation from
sub-horizontal to down-dip (Figures 3G and 6A–6D).
13
(A)
N
(B)
N
Figure 9. Photographs of tight to isoclinal intrafolial folds in the mafic–intermediate sheeted domain of the Totoltepec pluton.
Sigma-type hornblende porphyroclasts in mylonitic
tonalite and diorite indicate sinistral to top-to-SSE kinematics (Figure 3B). Further evidence for sinistral shear
is provided by C’-type shear bands (Figure 3A), asymmetrically boudinaged mafic and felsic dikes (Figures 3D
and 3F), and foliation deflection patterns (Figures 2G–2I
and 3E).
The predominant orientation of dikes in the main body
of the pluton is concordant with respect to the foliation
(Figure 6E). However, the overall range in the orientations
of individual dikes and the variations in the amount of
strain they display indicate the occurrence of several generations of dikes. Undeformed or gently folded dikes are
steeply dipping and have typical strikes of 36◦ –67◦ (measured clockwise from north), typically cutting the fabric
developed in the earlier intrusive phases (Figures 2E, 2F
and 2J), whereas dikes exhibiting pinch-and-swell structures or boudinage commonly occur at a low angle to
or in the foliation plane and have strikes of 71◦ –136◦
(Figures 2D, 2H, and 6E). Many dikes in the mafic–
intermediate sheeted domain contain a foliation that is
either sigmoidal or parallel with respect to dike margins,
irrespective of the orientation of the dikes relative to the
foliation of the surrounding rocks (Figures 2G, 2H, and 2J).
In a section perpendicular to the foliation and parallel
to the local sub-horizontal lineation, amphibole is locally
observed to be deflected into the plane of cross-cutting
dikes (Figure 2I).
Some areas in the Totoltepec pluton, particularly near
the contacts, exhibit brittle features (Figure 10), including tension gashes, faults, and associated brecciation
zones, jointing, small-scale horst-and-graben structures,
and quartz-carbonate veins that are attributed to hydraulic
fracturing and fluid mobilization late in the cooling
history of the pluton, and to episode(s) of regional
post-emplacement deformation. N-dipping fault planes
and associated N-plunging slickensides within the pluton
are consistent with top-to-the-S thrusting of the pluton
over metasedimentary rocks of the Tecomate Formation
as implied by the regional map (Figure 1B; Malone
et al. 2002). Muscovite from the low-angle, brittle–ductile
thrust contact between the Totoltepec pluton and the
Tecomate Formation yields a mid-Triassic age (Kirsch
et al. 2012). Locally, this shear zone is associated with
a Fe-P-REE deposit containing the mineral association
magnetite, apatite, barite, chlorite, quartz, chalcopyrite, and
14
M. Kirsch et al.
(A)
(B)
Gabbro
Trondhjemite
(C)
(D)
(E)
(F)
N
N
Figure 10. Late- to post-emplacement brittle features in the Totoltepec pluton. (A) Fault contact between marginal gabbro and main body
trondhjemite. (B) Small-scale, horst-and-graben structure in diorite. (C) Pegmatitic quartz-carbonate vein. (D) Jointing. (E) Mylonitic
thrust contact between the Totoltepec pluton and Tecomate Formation. (F) S-C fabrics in Tecomate Formation metasedimentary rocks
indicating top-to-S thrusting.
a cerium mineral (Table DR-4; see supplementary material at http://dx.doi.org/10.1080/00206814.2012.693247).
The mineralization is confined to two discrete, elongated
bodies of about 100 m length coinciding with strong
aeromagnetic anomalies (Servicio Geológico Mexicano
2004a,b).
Al-in-hornblende thermobarometry
Five samples of the Totoltepec pluton (one from the older,
marginal bodies and four from the younger, main body)
were selected for hornblende thermobarometry in order
to obtain an estimate of the emplacement temperatures
and pressures. For this purpose, coexisting hornblende and
plagioclase were analysed by electron microprobe wavelength dispersive spectrometry (WDS) at the Laboratorio
Universitario de Petrología (LUP), Instituto de Geofísica,
UNAM, Mexico City, Mexico. Representative analytical
data are presented in Tables 1, DR-1, and DR-2.
As one of the only available means of calculating
emplacement temperatures in calc-alkaline igneous rocks,
Blundy and Holland (1990) suggested that amphiboleplagioclase mineral pairs in equilibrium could be used as
a geothermometer. Accounting for non-ideal amphibole
solid-solutions, the geothermometer was later extended by
Holland and Blundy (1994), using two different exchange
reactions: (A) edenite + 4 quartz = tremolite + albite,
and (B) edenite + albite = richterite + anorthite. Whereas
thermometer A is only applicable to quartz-bearing rocks,
thermometer B can also be used for silica undersaturated
assemblages, but is restricted to temperatures in the range
of 500–900◦ C and plagioclase with XAn between 0.1 and
0.9 as well as hornblende with XNa(M4) > 0.03, AlIV <
1.8 atoms per formula unit (pfu), and Si in the range of
6.0–7.7 pfu. The precision of both thermometers is ±40◦ C
at 1–15 kbar (Holland and Blundy 1994).
The selected samples satisfy all compositional
constraints with respect to temperature and oxygen
fugacity, so the geothermometers of Holland and Blundy
(1994) are applicable. Because independent pressure data
are not available for the Totoltepec pluton, emplacement
temperatures were calculated at pressures ranging from
0 kbar to 15 kbar using the HB-PLAG program developed by Holland and Powell (http://www.esc.cam.ac.
uk/research/research-groups/holland/hb-plag). Minimum
and maximum pressures determined by the different
non-temperature-corrected Al-in-hornblende barometers
(Table 1) were used to define a narrow pressure interval,
from which average temperature values were calculated.
For sample TT-14 (gabbro from the older, marginal body),
which does not contain quartz and thus does not fulfil the
prerequisites of an Al-in-hornblende barometer, pressure
limits were adopted from the quartz-bearing tonalite
samples.
Geothermometric data yield essentially magmatic temperatures of mineral equilibration in all samples, ranging
from 716◦ C to 788◦ C for thermometer A and 719◦ C
to 843◦ C for thermometer B. Using thermometer B,
which according to Anderson (1996) yields more accurate results, the calculated median value of samples from
the main body of the pluton is 762 ± 40◦ C, whereas the
hornblende gabbro from the northern marginal body yields
a slightly higher median temperature of 807 ± 40◦ C. These
temperatures are broadly consistent with temperatures calculated from the Ti-in-zircon geothermometer of Watson
et al. (2006), yielding 713 ± 76◦ C (1σ error) for zircons of a quartz diorite from the main body of the pluton
and 731 ± 49◦ C for zircons from a marginal hornblende
15
gabbro sample (Table DR-6; see supplementary material at
http://dx.doi.org/10.1080/00206814.2012.693247).
Hammarstrom and Zen (1986) and Hollister et al.
(1987) were the first to conduct empirical studies that suggested a relationship between the total Al-content of calcic
amphiboles and the confining pressure. Subsequent experimental studies (Johnson and Rutherford 1989; Thomas
and Ernst 1990; Schmidt 1992) confirmed this correlation. Based on these experiments, a number of calibrations
for Al-in-hornblende barometry have been developed, with
which an intrusion depth can be calculated from microprobe measurements of amphiboles in granitoids. These
Al-in-hornblende barometers only consider the pressuredependent Tschermak substitution as an influence on the
Al-content of hornblende. Their application, therefore,
requires the presence of an appropriate buffer assemblage
(Qz-Kfs-Pl-Hbl-Bt-Tit/Mag and fluid melt) to limit the
thermodynamic degrees of freedom (Hammarstrom and
Zen 1986). Another important prerequisite is that anorthite compositions of coexisting plagioclase should range
between 25% and 35% (Hollister et al. 1987).
Anderson and Smith (1995) recognized that temperature also strongly influences the Al-content in hornblende
(edenite substitution), developing a new formula that is
based on calibrations of Johnson and Rutherford (1989)
and Schmidt (1992), but introducing a temperaturecorrection term to the pressure estimates. Apart from the
limitations mentioned above, the application of the Al-inhornblende barometer of Anderson and Smith (1995) is
furthermore restricted to amphiboles that crystallized at
high f O2 , i.e. have Fe# ≤ 0.65 and Fe3+ /(Fe3+ +Fe2+ ) ≥
0.25.
Hornblende crystallization pressures of the Totoltepec
pluton were calculated with the calibration of Anderson
and Smith (1995) and compared to the pressures
derived from Al-in-hornblende barometer calibrations
of Hammarstrom and Zen (1986), Hollister et al.
(1987), Johnson and Rutherford (1989), and Schmidt
(1992). The precision of these barometers is estimated
at ±0.5 to ±0.6 kbar (2σ ). All samples exhibit Fe#
and Fe3+ /(Fe3+ +Fe2+ ) ratios that indicate crystallization conditions under high oxygen fugacity, conforming
to the requirements of the method. However, all of the
selected samples from the Totoltepec pluton lack potassium
feldspar, and most of them do not contain biotite or titanite
(Table 1), so the calculated pressures should be considered maximum values (Anderson and Smith 1995). Three
samples contain plagioclase with a higher An content than
recommended, which may lead to lower Al content in
hornblende and thus yield pressures that are lower than
their true value (Anderson and Smith 1995). Temperature
corrections were applied using median temperature values
calculated by the amphibole-plagioclase thermometer of
Holland and Blundy (1994) (see above).
18.214033
−97.88385
18.215866
−97.88085
18.220783
−97.87857
18.258100
−97.85163
289 ± 2
289 ± 2
289 ± 2
306 ± 2
TT-14
TT-13a
TT-55
TT-54
TT-17
Hbl gabbro
HblPIQzMagIIm
Tonalite
HblPIMsQzIIm
Tonalite
HblPIQzTiMag
Tonalite
HblPIQzBtIIm
Hbl diorite
HblPIMsMaglim
Rock type
assemblagea
A1-P1
A2-P3
A3-P2
A1-P1
A2-P3
A3-P2
A1-P2
A2-P3
A3-P1
A1-P1
A2-P2
A3-P3
A1-P1
A2-P1
A3-P2
44.1
45.2
42.7
31.7
32.5
34.9
40.7
41.0
40.7
29.6
34.1
29.3
56.5
56.5
53.5
1.721
1.900
1.833
1.992
2.129
2.113
2.119
2.379
2.104
2.327
2.251
2.183
1.398
1.394
1.453
4.66
5.58
5.24
6.06
6.76
6.66
6.66
7.97
6.60
7.74
7.34
7.01
3.07
3.05
3.35
4.87
5.89
5.51
6.43
7.21
7.10
7.10
8.57
7.04
8.31
7.87
7.50
3.08
3.05
3.40
3.76
4.53
4.24
4.93
5.52
5.44
5.44
6.54
5.39
6.34
6.01
5.73
2.42
2.40
2.66
5.18
6.03
5.72
6.47
7.12
7.05
7.08
8.31
7.01
8.07
7.70
7.38
3.64
3.63
3.90
3.79
4.54
4.26
4.93
5.51
5.44
5.47
6.56
5.40
6.35
6.02
5.74
1.41
1.39
1.62
4.18
±
0.39
5.29
±
0.31
5.79
±
0.65
6.03
±
0.31
2.49
±
0.14
13.7
16.5
15.4
18.0
20.1
19.8
19.8
23.8
19.6
23.1
21.9
20.9
8.8
8.7
9.7
15.2
±
1.4
19.3
±
1.1
21.1
±
2.4
22.0
±
1.1
9.1
±
0.5
807
828
803
788
716
765
743
741
750
757
788
754
774
787
786
PHol
PJR
PSch
PAS c P avg Depthd
Depth T (ed tr)e
Pair
PI An Amp AI PHz b
Amp-PI (%)
(total) (kbar) (kbar) (kbar) (kbar) (kbar) (kbar) (km) avg (km) (◦ C)
836
843
822
780
719
766
755
752
757
752
788
746
802
815
807
833
±
11
755
±
32
755
±
3
762
±
23
808
±
7
T (ed-tr)f T avg
(◦ C)
(◦ C)
Notes: Preferred values indicated in bold font; a mineral abbreviations after Whitney and Evans (2010); b HZ – Hammerstrom and Zen (1986); Hol – Hollister et al. (1987); JR – Johnson and Rutherford
(1989); Sch – Schmidt (1992); c temperature correction in P(AS) based on average temperatures calculated from ed-ri temperatures (Holland and Blundy 1994) limited by PHZ , PHol , PJR , and PSch ;
d average crustal density is assumed as 2.8 g cm–3 ; e temperature calculated using plagioclase-hornblende geothermometer A (edenite-tremolite) of Holland and Blundy (1994); f temperature calculated using
plagioclase-hornblende geothermometer B (edenite-richterite) of Holland and Blundy (1994). Values in grey are unreliable due to lack of full mineralogical assemblage required for the thermobarometer.
18.208433
−97.89087
289 ± 2
Sample
Lat/Lon
(decimal
degrees)
Results of Al-in-hornblende geothermobarometry.
Age
(Ma)
Table 1.
16
M. Kirsch et al.
40 Ar/39 Ar
geochronology
Foliation-parallel muscovite between 180 and 250 μm in
size was separated from a Totoltepec pluton trondhjemite
sample E of Santo Domingo Tonahuixtla (TT-57: 18◦ 12
30 N, 97◦ 52 50 W). The mineral concentrate was
loaded into Al-foil packets and irradiated together with
the hb3gr hornblende standard (1072 ± 11 Ma) as a neutron flux monitor at the McMaster University research
reactor in Hamilton, Ontario, Canada. 40 Ar/39 Ar analyses were performed at the 40 Ar/39 Ar Geochronology
Research Laboratory at Queen’s University in Kingston
by a laser step-heating procedure using a a 30W New
Wave Research MIR 10–30 CO2 laser and a MAP
216 mass spectrometer. The data, corrected for blanks,
mass discrimination, and neutron-induced interferences,
are presented in Table DR-5; see supplementary material
at http://dx.doi.org/10.1080/00206814.2012.693247 and in
300
Apparent age (Ma)
Hornblende diorite and marginal hornblende gabbro
apparently yield much lower pressures than the other samples of the Totoltepec pluton, because both of these samples
have plagioclase compositions well outside the recommended range and, in addition, the diorite lacks quartz.
They are thus omitted from further consideration. The average hornblende Altot -content in tonalite from the main
body of the pluton is 2.177 ± 0.122. Resulting pressures calculated with calibrations without a temperature
correction term range from 5.3 to 7.9 kbar (Table 1).
The lowest values are obtained by the Al-in-hornblende
barometer of Johnson and Rutherford (1989), whereas
the formula of Hollister et al. (1987) yields the highest
values. Because the amphibole-plagioclase thermometer
of Holland and Blundy (1994) generates temperatures
well above the solidus of wet tonalite (Schmidt 1993), a
temperature correction according to Anderson and Smith
(1995) is reasonable. For samples within the recommended
compositional range of plagioclase as well as tonalite sample TT-55 with a slightly higher average XAn of 0.41,
an average pressure of 5.7 ± 0.6 kbar is obtained. This
pressure value is equivalent to the average pressure calculated with the Johnson and Rutherford (1989) barometer,
which is attributable to the fact that the experiments conducted by Johnson and Rutherford (1989) were calibrated
at temperatures between 720◦ C and 780◦ C, corresponding to the crystallization temperatures of hornblende from
the Totoltepec pluton. The calculated emplacement pressure of 5.7 ± 0.6 kbar for tonalite from the main body of
the pluton translates into a maximum emplacement depth
of 20.7 ± 2.2 km, assuming an average crustal density
of 2.8 g/cm3 . In summary, the main, ca. 289–287 Ma,
body of the Totoltepec pluton was emplaced at moderate temperatures (762 ± 40◦ C) and middle to high
pressures (≤5.7 ± 0.6 kbar) into middle crustal levels
(around 20 km).
17
Plateau age
283 ± 1 Ma
280
2σ errors
260
240
AOR-1107 /TT-57
Totoltepec pluton trondhjemite
Muscovite
220
0
10
20
30
40
50
60
70
80
90
100
Fraction 39Ar (%)
Figure 11. 40 Ar/39 Ar age spectrum for foliation-parallel
muscovite from Totoltepec pluton trondhjemite. For sample location see Figure 1B.
Figure 11. The plateau age and mean square of the
weighted deviates (MSWD) are obtained based on the following criteria, i.e. when the apparent ages of at least three
consecutive steps, comprising a minimum of 50% of the
total 39 Ar released, agree within 2σ error with the integrated age of the plateau segment (e.g. McDougall and
Harrison 1999; Baksi 2006). All age errors are quoted at
the 2σ level.
Muscovite from sample TT-57 yields an excellent
plateau age of 283 ± 1 million years (MSWD = 0.248),
defined by 11 fractions and representing 99.2% of the total
39 Ar released (Figure 11). The first step, comprising 31%
of atmospheric argon, is associated with a small amount
of contaminating phases as indicated by the corresponding
Ca/K ratio (Table DR-6). Assuming a relatively high cooling rate of 50◦ C/million years, consistent with the plateau
age spectrum, the closure temperature for muscovite from
this sample is calculated to be 390–400◦ C, using the equation developed by Dodson (1973). These data suggest that
by 283 ± 1 Ma, the main body of the Totoltepec pluton
had cooled through 390–400◦ C. Assuming a geothermal
gradient of 35◦ C/km, which is consistent with modelled
values for active portions of continental magmatic arcs
(e.g. Rothstein and Manning 2003), the calculated closure temperature for muscovite corresponds to a depth of
11.1–11.4 km. Given that barometric data indicate that the
main phase of the pluton was emplaced at around 20 km,
the 40 Ar/39 Ar data require a substantial and rapid uplift
and exhumation of the pluton between ca. 287 and 283 Ma
(around 2.25 km/million years).
Discussion
Structural context
The Totoltepec pluton is a component of a regional
Carboniferous–Permian continental arc extending from
18
M. Kirsch et al.
Guatemala to the southern USA (Kirsch et al. 2012). In the
southern Mexican portion of this arc, ca. 307–269 Ma
dextral shear along the >150 km-long, N–S-striking CFZ
that separates the Acatlán Complex from the Oaxacan
Complex (Figure 1A) has been well-documented (ElíasHerrera and Ortega-Gutiérrez 2002; Elías-Herrera et al.
2005). The significance of dextral shear along N–S-striking
faults within the Mexican Carboniferous–Permian continental arc is further supported by the presence of a
S-directed, dextral, sub-vertical, ca. 330–300 Ma fault
(Dowe et al. 2005) that separates the Palaeozoic Granjeno
Schist (a correlative of the Acatlán Complex; e.g. Nance
et al. 2007) from the ca. 1 Ga Novillo Gneiss (a correlative
of the Oaxacan Complex; e.g. Ortega-Gutiérrez et al. 1995)
in northeastern Mexico. In addition, the Totoltepec pluton is bounded to the W by the N–S dextral San Jerónimo
fault. Muscovite from the N–S Las Ollas fault lying to the
west yielded a 40 Ar/39 Ar age of 278 ± 2 million years
(Morales-Gámez et al. 2009).
The emplacement history of the Totoltepec pluton
can be explained within this regional context. The pluton
occurs in a crustal block bounded by two N–S-striking
dextral faults – the San Jerónimo fault to the west and
the Caltepec fault to the east (Figure 12). Dextral shear
along these boundary faults is inferred to have led to
(A)
SJF
CFZ
(B)
SJF
CFZ
the development of an intervening, sub-vertical, SW–NE
extensional fault (Figure 12A), which may have controlled
the emplacement of the Totoltepec pluton. Progressive
dextral movement on the bounding faults would have led
to clockwise rotation of NE–SW lines and objects in the
intervening block.
Interpretation of dike orientations
The systematic variation in dike orientation with progressive strain (Figure 6E) is consistent with the hypothesis
that the Totoltepec pluton was emplaced during deformation. The younger dikes, as identified by cross-cutting
relationships, are steeply dipping to vertical, undeformed
to gently folded, and are discordant with respect to the
foliation. These dikes exhibit a minimum clockwise angle
of 39◦ with respect to the N–S boundary faults, which is
inferred to represent the initial dike orientation. The perpendicular orientation of plagioclase and quartz adjacent
to the margins of late SW–NE pegmatitic dikes in the main
phase of the pluton (Figure 2G) attests to the orthogonal dilation accompanying initial intrusion. A permissive
mechanism of pluton emplacement along extensional fractures is also supported by the relatively minor crustal contamination of the mantle-derived, ultramafic–intermediate
(C)
SJF
A’
B’
C’
A
B
C
CFZ
(D)
SJF
CFZ
D’
thrust
39°
?
ca. 306 Ma
ca. 289 Ma
ca. 287 Ma
ca. 283 Ma
entrained
blocks
gabbro/
hornblendite
thrust
diorite
tonalite
A
D
A’
B
trondhjemite
B’
C
C’
D
D’
Figure 12. Plan-view structural models and hypothetical cross-sections illustrating the emplacement of the Totoltepec pluton. (A)
Intrusion of early mafic to ultramafic magma along a lineament in the transfer zone between the dextral, N–S-striking San Jerónimo
Fault (SJF) and the Caltepec Fault Zone (CFZ). (B) Ascent of several sheet-like mafic to intermediate magma batches during regional
transtension along a vertical, initially extensional SW–NE fault that became a WSW–ENE, sinistral cross-fault, rotating clockwise due
to dextral displacement on N–S boundary faults. (C) Synkinematic emplacement of a larger, more felsic batch of melt during continued
clockwise rotation of a cross-fault in the regional transtension zone. (D) Transference of dextral motion on the SJF to the CFZ, resulting
in south-southeastward thrusting of the pluton and rapid uplift/exhumation.
rocks and the lack of xenoliths or xenocrystic zircon in
marginal and main phases of the pluton (Kirsch et al.
2012).
In contrast, older, sub-vertical dikes are folded, variably sheared, foliation-concordant bodies that appear to
have been reoriented during progressive dextral shear. With
progressive dextral shear on the bounding faults, these
NE-striking dikes would have initially rotated clockwise
into a sector involving sinistral shear (Figure 12B), which
is consistent with the orientation of the sigmoidal internal fabric of some dikes (Figures 2G and 2H) and the
locally observed deflection of amphibole into dike planes
(Figure 2I). Further clockwise rotation of the dikes led to
the development of extensional structures, such as boudinage and pinch-and-swell.
In order to assess the significance of the dike array in
terms of the strain regime that accompanied its emplacement, we compare the dike patterns in the Totoltepec
pluton to theoretical finite strain geometries and predicted material line sectors for simple shear, transpression,
and transtension (Figure 6E). The present surface of the
Totoltepec pluton limits the strain analysis to 2D rather
than a comprehensive 3D analysis (Kuiper and Jiang 2010).
The ca. 307–269 Ma dextral shear along bounding vertical N–S faults was synchronous with emplacement of the
Totoltepec pluton. If the movement on the N–S faults was
purely strike–slip, the transition from the shortening to the
extensional field of the finite strain ellipse, i.e. between the
orientation of folded dikes, and dikes that have been folded
and subsequently boudinaged, should occur at angles of 90◦
to the N–S Caltepec and San Jerónimo faults. However,
in the Totoltepec pluton, this transition occurs at angles of
73◦ , i.e. before the clockwise rotation reaches 90◦ relative
to the N–S-striking shear zone boundaries. This geometrical distribution pattern of material line sectors is indicative
of transtensional deformation (Figure 6E; Kuiper and Jiang
2010).
Transtensional strain within the crustal block that
contains the Totoltepec pluton is consistent with the
prolate spheroid shapes in pebbles of metaconglomerates in the Pennsylvanian–Middle Permian Tecomate
Formation north and south of the Totoltepec pluton
(Morales-Gámez et al. 2009). The long axes of these
clasts are oriented parallel to the shallow NNE-plunging
stretching lineation in the metasedimentary rocks of
the Tecomate Formation. A sericitic phyllite from the
Tecomate Formation northwest of the Totoltepec pluton
yielded a 40 Ar/39 Ar whole-rock age of 263 ± 3 million
years (Morales-Gámez et al. 2009) and may record syntectonic growth of sericite. However, earlier transtensional
deformation is indicated by the ca. 306 million year age
of the mafic part of the Totoltepec pluton, suggesting
that dextral movement along N–S striking faults in the
regional arc was long-lived. Three components of strain
are documented in the Totoltepec pluton: (1) NW–SE
19
extension, as indicated by the orientation of late pegmatitic
dikes; (2) sub-vertical emplacement, as indicated by
down-dip hornblende mineral elongation lineations; and
(3) sub-horizontal, WSW–ENE-directed sinistral shear, as
indicated by along-strike mineral lineations and a range
of different kinematic indicators. As there is no evidence
for one set of lineations overprinting another, and as both
sets of lineations are defined by magmatic hornblende, i.e.
formed during the early stages of pluton crystallization,
these three components of shear are inferred to belong to a
single episode of deformation. Although only 2D data are
available for the Totoltepec pluton, the vorticity axis was
probably oblique to these axes, indicating triclinic deformation (e.g. Jiang and Williams 1998; Lin et al. 1999).
In this context, the relative predominance of lineations with
shallow and steep plunges in different parts of the mafic–
intermediate sheeted domain may be attributed to either
deformation-path partitioning into simple shear-dominated
and pure shear-dominated movement components across
the shear zone (Lin and Jiang 2001), or superimposition
of the sinistral shear component on vertical emplacement.
The latter is consistent with the clockwise rotation of the
pluton, and the lack of significant lateral displacement in
the 2D outcrop shape of the pluton, suggesting that the
sinistral component during emplacement was minor compared with the amount of vertical extension. The amount of
vertical emplacement is constrained by thermobarometric
and geochronological data, which indicate a rapid (around
2.25 km/million years) exhumation of the pluton between
ca. 287 Ma and ca. 283 Ma. Using the present horizontal width of the main plutonic phase (around 4 km) as a
measure for NW–SE extension yields around 20% of E–W
extension across the zone. More structural data are required
to more rigorously quantify the strain in the pluton.
Ascent/emplacement mechanism
Geochronological data indicate that the Totoltepec pluton
was assembled by at least two magmatic episodes separated
by around 17 million years. According to thermal modelling results (e.g. Stimac et al. 2001), this time span of
pluton construction exceeds the thermal lifetime of a large
magma reservoir, indicating that the compositional variability between the main and marginal phase of the pluton
is not due to in situ differentiation of a steady-state magma
chamber, but represents at least two compositionally distinct magma pulses.
Field evidence indicates that the younger intrusion
was also generated by a series of different magma batches
ranging from felsic to mafic in composition. Physical
interaction between magmatic increments of this main
plutonic phase is indicated by the occurrence of autoliths,
microgranular enclaves, and composite dikes. The crystallization ages obtained for various phases of the main
plutonic body are the same within error (Yañez et al. 1991;
20
M. Kirsch et al.
Keppie et al. 2004a; Kirsch et al. 2012). However, contacts
between undated individual sheets, dikes, and enclaves
are usually sharp and locally show chilled margins or
reaction rims, suggesting that magmatic injections were
sufficiently spaced in time for preceding increments to cool
and solidify. On the other hand, within the compositionally
banded zone, which on the basis of its field relationships,
steepness of banding, and lack of ‘sedimentary’ structures
(e.g. Barbey 2009), is interpreted as having originated by
multiple dike injections, feldspar phenocrysts grow across
dike margins, suggesting that some magmatic increments
were intruded before the igneous host was completely
crystallized.
These relationships suggest that diking was an important emplacement mechanism, at least for the highly
heterogeneous mafic–intermediate sheeted zone in the
southern part of the pluton, where individual narrow,
sub-vertical sheets can be traced for tens of metres along
strike and locally show tapering terminations (e.g. Paterson
and Miller 1998; Petford et al. 2000). An emplacement
mechanism involving magma migration through propagating dike conduits is consistent with the regional structural
context indicating extension oblique to strike–slip faults,
which favours the emplacement of plutons as multiple
injections with thin, dike-like geometry (e.g. Pitcher and
Berger 1972). Trondhjemitic rocks in the interior of the
pluton are more voluminous and more homogeneous in
composition with the marginal mafic–intermediate sheeted
zone. This outcrop pattern agrees with thermal models
that predict a transitory sheeted-dike phase followed by
the formation of an ephemeral, central magma chamber (Hanson and Glazner 1995; Coleman et al. 2004).
However, the identification of rare felsic dikes and the
presence of different microstructural types within this
domain suggest that the trondhjemitic part of the pluton
may also have an episodic emplacement history. More
generally, Bartley et al. (2008) point out that intrusive
contacts between magmatic increments may be more
numerous than is apparent in the field because internal
contacts may have become cryptic due to recrystallization
processes related to the extended periods of high temperatures that accompany slow incremental growth of a
pluton.
Synthesis/intrusive sequence
Geochronological (Kirsch et al. 2012), combined with
thermobarometric, structural, and kinematic data, lead us
to propose the following sequence of intrusive events.
Early mafic–ultramafic rocks were emplaced at ca. 306 Ma
along a crustal lineament (Figure 12A). At ca. 289 Ma,
renewed magmatic activity in a transtensional regime
within the regional magmatic arc led to several successive
sheet-like intrusions of dike-fed, mafic–intermediate magmas (Figure 12B). Heat provided by mafic–intermediate
magma and regional arc activity (Solari et al. 2001; ElíasHerrera et al. 2005; Rosales-Lagarde et al. 2005; Solari
et al. 2010) may have led to crustal melting and the
formation of felsic magma at ca. 287 Ma. The stabilization of partially molten pathways (e.g. Miller and Paterson
2001) potentially allowed for these voluminous, more felsic batches of melt to become wedged between the older
mafic–intermediate rocks (Figure 12C). Parts of the older
mafic–ultramafic phase may have become entrained in the
rising felsic melts, physically disaggregated by diking,
rotated and dispersed along the margin of the pluton.
Entrainment of the mafic–ultramafic phase is consistent
with (1) the presence of inherited zircons of ca. 306 Ma age
in ca. 289 Ma rocks from the pluton interior (Kirsch et al.
2012), suggesting that these older mafic–ultramafic blocks
were partly assimilated; (2) the scattered spatial distribution of the marginal bodies; and (3) the visible evidence
that the marginal bodies are intruded by felsic dikes. The
occurrence of undated boundinaged folded dikes, folded
dikes, and undeformed dikes suggests that dike intrusion
started with, and continued after, intrusion of the main
phase. Immediately following intrusion, clockwise rotation of the main phase of the pluton into its current
WSW–ENE orientation produced a vertical foliation and
horizontal lineation as well as intrafolial folds in the pluton.
Fabric development occurred synchronously with deformation over a large temperature range from magmatic to
low-temperature conditions and was spatially diachronous.
This is consistent with the continuum from magmatic to
solid-state foliations and the parallelism between these
respective fabrics (e.g. Paterson et al. 1989; Vernon et al.
1989; Miller and Paterson 1994; Tribe and D’Lemos 1996).
With decreasing temperature, the plutonic body may have
become increasingly coupled to the country rocks (e.g.
Tribe and D’Lemos 1996; Barros et al. 2001), which led
to the overprinting of igneous structures by solid-state
fabrics. Deformation was concentrated in zones of competency contrast, i.e. the mafic–intermediate sheeted domain
near the pluton margin, where it produced discrete mylonite
zones (Figure 3).
Structural evidence within these mylonite zones, such
as the local development of tectonic down-dip lineations
with kinematic indicators of top-to-SSE transport, suggests that in the last stages of the emplacement history,
thrusting may have developed locally within the regional
transtensional environment. Thrusting may be associated
with a decrease of slip along the San Jerónimo fault and
resulting transfer of dextral displacement onto the Caltepec
fault (Figure 12C). This transfer may have led to (1) termination of magma supply by truncating the magma conduit,
although regional magmatism occurred elsewhere in the
arc and (2) substantial (around 2.25 km/million years)
uplift of the pluton between ca. 287 Ma and ca. 283 Ma as
inferred by Al-in-hornblende thermobarometry combined
with 40 Ar/39 Ar geochronology.
Regional significance
Transtensional deformation is a common feature of
magmatic arcs, resulting from oblique convergence and
strain partitioning at plate margins (e.g. Teyssier et al.
1995; Dewey 2002). The southern Mexican portion of the
extensive Carboniferous–Permian continental arc exhibits
a well-pronounced arc-parallel structure of N–S oriented, dextral strike–slip faulting and synkinematic plutons
emplaced along these faults. The Totoltepec pluton is interpreted to have been emplaced along a SW–NE extensional
fault that was synchronous with the dextral shear along
N–S fault zones, and is thus an example of arc-transverse
strike–slip tectonics in the southern Mexican arc. The
geochemistry of the Totoltepec pluton, which is isotopically more primitive than coeval igneous rocks elsewhere
in the regional magmatic arc (Kirsch et al. 2012), and
the intrusive history involving the incremental injection
of several sheet-like magma batches into mid-crustal levels during transtensional deformation, followed by local
thrusting resulting in uplift and exhumation, may be characteristic of pluton emplacement in such a specialized
tectonic environment and may be utilized in identifying
similar tectonic settings within continental arcs.
Acknowledgements
MK thanks Maria Helbig for invaluable assistance in the field and
support throughout the writing process. MK also acknowledges
the helpful discussions with Uwe Kroner, Luigi Solari, Fernando
Ortega-Gutiérrez, Harald Böhnel, Axel Renno, and Ángel F. Nieto
Samaniego. Carlos Linares provided technical assistance during
microprobe work at the Laboratorio Universitario de Petrología,
UNAM. This study was funded by CONACyT and PAPIIT
grants to JDK, and by NSERC discovery grants to JBM and
JKWL.
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E V E N T O S D E L PA L E O Z O I C O TA R D Í O H A S TA E L
MESOZOICO TEMPRANO EN LA PERIFERIA DE
PA N G E A
Guía de la excursión geológica: Keppie, J.D., Galaz-Escanilla, G., Helbig,
M., y Kirsch, M. (2012). Late Paleozoic–Early Mesozoic of the Acatlán and
Ayú complexes, southern Mexico: events on the periphery of Pangæa synchronous with amalgamation and breakup. GSA Cordilleran Section, 108th
Annual Meeting, Field Trip 1, 31 March – 4 April, Geological Society of
America, IGCP Project 597, 17 p.
J. Duncan Keppie: líder y organizador de la excursión; concepción y
diseño de la guía de excursión.
Gonzalo Galaz-Escanilla: co-líder de la excursión; descripción de las
paradas 3-1 a 3-7; redacción de las figuras 7 y 8.
Maria Helbig: co-líder de la excursión; descripción de las paradas 1-1
a 1-6; redacción de las figuras 3, 4 y 5.
Moritz Kirsch: co-líder de la excursión; descripción de las paradas 21 a 2-8; elaboración de la figura 6; con respecto a los nuevos datos
de una unidad metamórfica del Misisipiense en la parte oriental del
área de estudio: trabajo de campo incluyendo mapeo y muestreo para
la geocronología 40 Ar/39 Ar; análisis geoquímico e isotópico; adquisición de datos de los análisis 40 Ar/39 Ar incluyendo la separación de
minerales, el análisis y la interpretación de datos.
58
4
GSA Cordilleran Section, 108th Annual Meeting
Field Trip 1
31 March–4 April 2012
Amalgamation and Breakup of Pangæa:
the type example of the supercontinent Cycle
International Geological Correlation Program Project #597: Late Paleozoic–Early Mesozoic of the Acatlán and Ayu
complexes, southern Mexico: events on the periphery of Pangæa synchronous with amalgamation and breakup
J. Duncan Keppie
Gonzalo Galaz-Escanilla
Departamento de Geología Regional, Insituto de Geología, Universidad Nacional Autónoma de México, 04510 Mexico, D.F.
Maria Helbig
Mortiz Kirsch
Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, 76230 Querétaro, QRO, Mexico
INTRODUCTION
There is widespread acceptance that between 300 and 200 million years ago, all of
the Earth’s continental land masses were assembled into a giant supercontinent, Pangæa, surrounded by a superocean, Panthalassa. However, different configurations
have been proposed, e.g., Pangæa A1, A2, B, and C (Fig. 1A). Reconstructions based
on Mexican paleomagnetic data have been used to support both A and B models:
(a) PANGEA-A. A Permo-Triassic Pangea-A reconstruction where southern
Mexico lies approximately in its present location relative to North America
(Fang et al., 1989, Alva-Valdivia et al., 2002);
(b) PANGEA-B. A Pangea-B reconstruction placing southern Mexico off eastern
Canada during the Jurassic (Fig. 1B: Böhnel, 1999).
There are also Middle American variants of the Pangea-A reconstruction:
(i) southwestern Mexico is placed either along the western margin of Pangea (Fig. 1C and 1D: Keppie, 2004, Keppie et al., 2008, 2010), or within
Pangea between the Maya terrane and southern USA (Fig. 1E: TalaveraMendoza et al.,2005, Vega-Granillo et al., 2007, 2009);
(ii) the Yucatan block is placed either within Pangea along the southern margin of USA (Fig. 1F: Pindell and Dewey, 1982), or on the western margin
of Pangea during the mid-late Permian migrating into the Gulf of Mexico
by the Middle Jurassic (Steiner, 2005);
(iii) the Chortis block has generally been placed off southwestern Mexico on
the western marin of Pangea (Fig. 1E)(e.g., Pindell and Dewey, 1982), or
within the within Pangea along the eastern margin of Mexico (Fig. 1G:
Keppie and Keppie, in review).
On this field trip we will examine the evidence for subduction-related tectonics
during the Pennsylvanian-Jurassic in the Ayu and Acatlán complexes, which suggests
proximity to an ocean that is more consistent with the Pangea-A model (Fig. 2).
1
2
Keppie et al.
A
C
B
D
350–330 Ma
E
300–270 Ma
G
F
Figure 1. Reconstructions of Pangea by various authors.
Amalgamation and Breakup of Pangæa: the type example of the supercontinent Cycle
3
Figure 2. (A) Terranes of Middle America (after Keppie, 2004); (B) Ages od units in the Acatlán Complex; (C) Map of the Acatlán Complex
(modified after Keppie et al., 2010) showing the field trip route.
4
Keppie et al.
DAY 1
Maria Helbig and J. Duncan Keppie
The Triassic-Jurassic Ayú Complex Southern Mexico:
Evidence for Deposition on the Proximal Margin of a
Backarc Basin, Underthrusting and Extrusion into the
Acatlán Complex during the Breakup of Pangea-A
Helbig, M, Keppie, J.D., Murphy, J.B., and Solari,
L.A., in press. U-Pb geochonological constraints on the
Triassic–Jurassic Ayú Complex southern Mexico: derivation
from the western margin of Pangea: Gondwana Research.
ABSTRACT
Rocks of the newly designated Ayú Complex are located in
the eastern Mixteca terrane (southern Mexico), and comprise
polyphase-deformed turbiditic rocks (Chazumba Lithodeme)
that are intercalated with boudinaged ortho-amphibolites. In
the south, the metasedimentary sequence is affected by partial
melting and grades into the ~171 Ma Magdalena Migmatite.
Migmatitzation was accompanied by 171–168 Ma granitoid
minor intrusions and pegmatites with inherited zircon populations of ca. 260–290, 320–360, 420–480, 880–990, and 1080–
1250 Ma that are also found in the Chazumba Lithodeme.
Detrital U/Pb zircon ages from the migmatized and unmigmatized Chazumba Lithodeme yielded clusters of ca. 297, 266,
250, 214, 198, and 192 Ma, suggesting Upper Triassic—Lower
Jurassic deposition. The MORB tholeiitic geochemistry of
the amphibolites within the Chazumba Lithodeme indicates
a back-arc environment with sedimentation occurring along
the inboard rifted passive margin, the Upper Triassic–Lower
Jurassic detrital zircons being derived from a contemporaneous, outboard magmatic arc. These characteristics suggest correlation with the lens-shaped Central terrane typified by the
Potosi turbiditic fan in the rift-passive margin of Pangea that
is absent west of the Mixteca terrane. The presence of this arc
requires deposition adjacent to a subducting ocean and thus
supports a Pangea-A reconstruction. Early Jurassic flattening
of the subduction zone is inferred to have led telescoping of
the Triassic–Early Jurassic back arc basin, during which the
Chazumba Lithodeme was thrust beneath the Pangean margin
where it was metamorphosed under amphibolite facies metamorphic conditions. It is further inferred that Middle-Upper
Jurassic steepening of the subducting zone led to tectonic
exhumation of the Chazumba Lithodeme by normal faulting
along the reactivated Providencia Shear Zone. Deposition,
underthrusting and exhumation of the Chazumba Lithodeme
are synchronous with the breakup of Pangea and the opening
of the Gulf of Mexico.
STOP 1-1 (W97.78834, N17.9387426: Fig. 3)
Location: Road between Sta. María Ayú and
Ahuehuetitlán, riverbed of Río La Peña.
Micaceous schists and garnet-biotite gneisses are intercalated with boudinaged amphibolites, that underwent migmatization at ~171 Ma (leucosome dated by Keppie et al., 2004) and
formed a mappable unit, called the Magdalena Migmatite. This
tectonothermal event was accompanied by syntectonic intrusion
of granitic, granodioritic and dioritic dikes and sheets (Yañez
et al., 1991). A granite dike that cuts the paleosome yielded only
one igneous zircon of 171 ± 4 (Middle Jurassic), whereas the
rest of the dated grains are inherited zircons. Two paleosome
samples of the Magdalena Migmatite yielded youngest detrital
zircons of ~198 Ma (Early Jurassic) and 214 Ma (Late Triassic),
respectively. Amphibolites were previously dated by Keppie
et al. (2004) and showed 40Ar/39Ar cooling ages of 150 ± 2 Ma
for biotite and 136 ± 2 for hornblende, suggesting rapid exhumation. Geochemically, amphibolites sampled across the Ayú Complex are MORB-like, rift-related tholeiites (Helbig et al., 2010).
The majority of the ortho-amphibolites have jagged NMORBnormalized REE patterns that imply contamination either by a
crustal and/or subduction component and suggest a formation in
a back-arc basin.
STOP 1-2 (W97.807052°°, N17.9987634°°: Fig. 3)
Location: short road stop east of Tetaltepec.
Structural relationships in the Magdalena Migmatite: Large
scale, close to open, upright to gently inclined parasitic fold (F4)
that folds the leucosome and boudinaged S3-parallel granite
sheets.
STOP 1-3 (W97.830789°°, N18.036058°°: Fig. 3)
Location: Riverbed, south of San Miguel Ixtápan.
Partially molten, and strongly deformed metasedimentary
rocks that are intruded by granodiorites and pegmatites. Xenoliths are probably the metasedimentary host rock and show internal foliation as well as partial melting of the fertile domains.
40
Ar/39Ar dating of a pegmatite and a granitic sheet yielded
167 ± 2 Ma for muscovite, and 155 ± 5 Ma for biotite (Keppie
et al., 2004).
STOP 1-4 (W97.832239°°,N18.0421378°°: Fig. 3)
Location: Road section, south of San Miguel Ixtapan.
Outcrop exhibits a dike that cuts across the micaceous
schists and feeds a granite sheet. The emplacement of the granite
sheet is parallel to the main foliation, inflating the surrounding
metapelitic host rock. The dike continues its way into the hanging metasedimentary host rock. Where in the contact with the
host rock, the dike is overprinted by the same fabric as in the
metasedimentary rocks. The rock is affected by later brittle normal block faulting. The fabric-parallel granite sheets show sharp
contacts with the metapelites and exhibit minor pinch-and-swell
structures and a distinct tectono-magmatic foliation at their margins suggesting stress-related emplacement.
–97°48′
–97°42′
18°00′
18°06′
18°12′
X –97°54′
5
X′
X
X′
Figure 3. Geological map and section of the Totoltepec-Ayu area, southern Mexico showing field trip stops (modified after Helbig et al., in press).
6
Keppie et al.
STOP 1-5 (W97.828639°°, N18.0526397°°: Fig. 4)
Location: Foothills of the Cerro de La Peña
(Cenozoic volcanic plug), north of Tejepillo;
San Miguel Ixtapan road exit to Tultitlán.
Micaceous schists intercalated with minor quartzites are intruded by granites, leucogranitic and aplitic dikes. A granite dike
cuts a tight, recumbent E-trending F3 fold in the metasedimentary
host rock. Small leucogranite veins that probably originate from
the dike are parallel to the folded S2 fabric. These relationships
suggest that the intrusion was syn- to late-tectonic with respect
to F3. The granite is characterized by zircon inheritance and the
crystallization age is inferred from the youngest grain with an
age of 168 Ma. U-Pb detrital zircon analyses of a psammitic
and a pelitic mica schist yielded maximum depositional ages of
~269 Ma and ~263 Ma (Middle Permian), respectively.
In the hanging wall, the mafic-ultramafic Tepejillo lens lies
structurally as a nappe above the Chazumba Lithodeme (Keppie
et al., 2004) and consists of four bodies that crop out along the
foothills of Cenozoic volcanic plug (C. La Peña). The Tepejillo
lens comprises coarse crystalline ultramafic (mainly dunite) to
gabbroic rocks that are cut by diabase dikes. Geochemically,
they are interpreted as part of a cumulatic body intruded into
the lower continental crust (Keppie et al., 2004). The contact between the metasedimentary rocks of the Chazumba Lithodeme
and the Tepejillo lens has been mapped as a folded thrust (Keppie et al., 2004). The Tultitán lens, 4 km to the northeast of
the Tepejillo lens, consists of massive amphibolite and a core
of metamorphosed norite. One concordant U-Pb LA-ICP-MS
analysis of a prismatic tip of a euhedral zircon from a metanorite
yielded an age of 174 ± 1 Ma, which is interpreted as age of
intrusion for both lens (Keppie et al., 2004). Biotite from a gabbroic dike of the Tepejillo lens yielded a 40Ar/39Ar cooling age
of 166 ± 2 Ma, whereas muscovite from a granite dike yielded
a 40Ar/39Ar age of 161 ± 2 Ma (Keppie et al., 2004), suggesting
excess argon in the biotite. Lower power increments of Late Cretaceous to Tertiary age can be observed in almost all 40Ar/39Ar
analyses, implying that the Ayú Complex was affected by a later
deformational event.
STOP 1-6 (W97.899842°°, N18.113004°°: Fig. 5)
Location: road section near the town La Providencia,
on the road between Petlalcingo and Tonhuixtla.
Reactivation of a Triassic S-vergent thrust fault as a listric normal fault in the Middle-Late Jurassic. The Providencia
shear zone forms a major structural feature between rocks of the
Acatlán Complex (Tecomate Formation and Cosoltepec Formation) and the Ayú Complex and comprises weathered mylonites.
A micaceous metapsammite just south of the shear zone
yielded only seventeen concordant analyses. Relatively narrow
age spectra ranging from 194 to 339 Ma were obtained with the
two youngest grains (190 ± 4, 193 ± 4 Ma) forming a mean of
192 ± 19 Ma (Early Jurassic). To the north of the shear zone, a
mylonitic phyllite yielded a youngest detrital zircon age of 314 ±
4 Ma, which lies within the error of the mean of the three youngest grains with an age of 321 ± 30 Ma (Late Mississippian/Early
Pennsylvanian). A graphite- and feldspar-bearing mylonitic
metasedimentary rock, yielded two youngest detrital zircon ages
of 281 ± 4 Ma and 295 ± 8 Ma with a mean age of 284 ± 71 Ma
(Early Permian).
The presence of a major shear zone (Providencia Shear Zone)
that separates the Acatlán Complex from the Ayú Complex was
previously mapped as a thrust based on s-c fabrics in the hanging block (Malone et al., 2002; Keppie et al., 2004). However,
40
Ar/39Ar cooling ages for amphibole of an amphibolite lens and
muscovite from micaceous schists, north of the shearzone yielded
cooling ages of ~214 Ma and ~224 Ma, respectively (Keppie
et al., 2004). These fabrics are Late Triassic, and thus developed
before or during the deposition of the Chazumba Lithodeme. It is
envisaged that this Triassic shear zone was reactivated during or
after the Middle Jurassic as a listric normal fault and formed the
upper boundary of the exhuming Chazumba Lithodeme.
DAY 2
Moritz Kirsch and J. Duncan Keppie
Lower Permo-Carboniferous Arc Magmatism and
Sedimentation on the Margin of Pangea-A
Kirsch, M., Keppie, J.D., Murphy, J.B., and Solari, L.A.
in press. Permian-Carboniferous arc magmatism and
basin evolution along the western margin of Pangea:
geochemical and geochronological evidence from the
eastern Acatlán Complex, southern Mexico: GSA Bulletin.
ABSTRACT
The Late Paleozoic evolution of Mexico records part of a
continental arc that extends along the western margin of Pangea from western USA to the northern Andes. In the Acatlán
Complex of southern Mexico, an arc assemblage consisting
of a Permo-Carboniferous intrusion (Totoltepec pluton) and
Permian sedimentary rocks (Tecomate Formation) offers a rare
opportunity to examine events along the periphery of Pangea at
the critical stage of final amalgamation.
The Totoltepec pluton ranges in composition from hornblendite and hornblende gabbro through diorite to tonalite,
trondhjemite, granodiorite and monzo-granite. U-Pb LA-ICPMS zircon analyses yield concordant ages of 306 ± 2 Ma in
minor marginal mafic to ultramafic rocks and 289 ± 2 Ma for
the main, more voluminous mafic to felsic intrusion. Major and
trace element geochemistry of the Totoltepec rocks exhibit a
tholeiitic to calc-alkaline character, high LILE/HFSE and flat
REE patterns, which is typical of arc-related magmas. The precursor gabbroic rocks display εNd(t) values ranging from +1.3
to +3.3 (t = 306 Ma), whereas rocks from the main body of the
pluton have εNd(t) values between −0.8 and +2.6 (t = 289 Ma).
7
A′
B
B′
A
A′
A
B
B′
Figure 4. Stop 1-5: geological map, age data, and section of the Tepejillo ultramafic lens (after Keppie et al., 2004).
18°07′30″
18°07′00″
00
15
m
–97°54′00″
400
m
50
14
m
–97°53′30″
Figure 5. Stop 1-6: geological map and geochronology of the La Providencia shear zone (modified after Helbig et al., in press)
0m
1 40
1450
m
1
–97°54′30″
18°06′30″
8
Keppie et al.
9
All of the samples are variably affected by wall rock assimilation, mixing and fractionation processes, but are more juvenile compared to contemporaneous arc-related igneous rocks
in southern Mexico, suggesting the pluton was emplaced into
thinner crust in a less mature part of the arc or along a fault that
acted as a conduit for mantle-derived melts.
The Tecomate Formation consists of low-grade, poorly
sorted, compositionally immature and largely unweathered
metapsammites and metapelites. Several factors indicate derivation from the Permo-Carboniferous arc: (i) an arc-related
geochemistry, (ii) εNd(t) values ranging from −5.7 to +0.3
(t = 280 Ma) that overlap those of the Totoltepec pluton, and
(iii) detrital zircons with predominantly Permo-Carboniferous
ages. The depositional age of the Tecomate Formation is constrained between the youngest detrital zircon population (ca.
280 Ma) and a published Ar/Ar age of 263 ± 3 Ma from the Tecomate Formation in the adjacent area. However, a metapsammite
sample from the base of the Tecomate Formation yielded only
Proterozoic zircons, indicating that deposition may have initiated earlier. Possible correlative sequences that may have been
deposited in a similar peri-arc setting include the latest Pennsylvanian to Middle Permian Tecomate Formation type area, the
latest Devonian to Lower Permian Patlanoaya Group, the Early
to Middle Permian Tuzancoa Formation, the Middle Permian
Los Hornos Formation, and the Olinalá Formation of Middle to
Upper Permian age.
ment along a transpressional fault. Hornblende-bearing diorites
and tonalites within the low to medium-temperature solid-state
domain in the southern part of the pluton exhibit a compositional and textural banding that is interpreted to have formed
by a combination of steep igneous layering, layer-parallel dike
injection and melt-enhanced deformation.
Although we were unable to document any regional-scale
structures that may have controlled its intrusion, the timing and
emplacement mechanism of the Totoltepec pluton is similar
to that reported for syn-tectonic Late Carboniferous to Early
Permian plutons along the Caltepec Fault zone that separates
the Mixteca terrane from the Oaxacan Complex. Strike-slip tectonism along this fault may be associated with oblique subduction of the paleo-Pacific beneath the western margin of Pangea.
Kirsch, M., Keppie, J.D., Murphy, J.B. and Lee, J.K.W., in
preparation. Structural history of the arc-related Totoltepec
pluton, Acatlán Complex, southern Mexico: Syntectonic
emplacement along a mid-crustal transpressional shear zone.
STOP 2-2 (W97.890711°°, N18.208455°°: Fig. 6)
ABSTRACT
The 306–289 Ma tholeiitic to calc-alkaline Totoltepec pluton in the eastern Acatlán Complex, southern Mexico, is part
of a Permo-Carboniferous continental magmatic arc along the
western margin of Pangea. The pluton is a well-exposed, composite, felsic to ultramafic intrusive suite containing a conspicuous mesoscopic fabric, making it an ideal place to study the
relationship between tectonic processes in magmatic arcs and
pluton emplacement.
We use an integrated approach combining field observations, structural measurements, analysis of micro-fabrics, as well
as Al-in-hornblende thermobarometry and 40Ar/39Ar thermochronology to decipher the structural evolution of the Totoltepec pluton. The data suggest that the pluton was emplaced in
~20 km depth and rapidly uplifted to allow it to cool to ~400 °C
within 6 ± 2 Ma. The elongate pluton shape, parallel, decreasing temperature fabrics, similar crystallization and deformation
ages and the rapid exhumation of the pluton speak for a syntectonic emplacement. A subvertical, fanning foliation and subhorizontal to subvertical lineations as well as the presence of
internal, margin-parallel sinistral shear zones suggest emplace-
STOP 2-1. (W97.88385°°, N18.214033°°: Fig. 6)
Transpressional shear zone within the Totoltepec pluton near
Santo Domingo Tonahuixtla. Here, strongly banded and foliated
hornblende-bearing diorite and tonalite is intruded by felsic and
mafic dikes at low angles to the WSW-striking planar fabric.
Hornblende fish and asymmetrically boudinaged dikes consistently display sinistral kinematics. The crystallization age of the
mafic rocks give an age of 289 ± 2 Ma (Keppie et al., 2004),
whereas foliation-parallel muscovite in trondhjemite (1 km due
SE) yield a 40Ar/39Ar age of 283 ± 1 Ma.
Aplitic dikes intruding megacrystic hornblende diorite/
tonalite north of Santo Domingo Tonahuixtla. Dikes are mostly
foliation-parallel, but are locally observed to cut the foliation at
low angles. Some dikes contain an internal tectono-magmatic
fabric parallel to the dike wall and dike-host contacts are sharp
to irregular suggesting dike emplacement was syntectonic and
occurred prior to complete crystallization of the host. The megacrystic hornblende-bearing rocks are laterally traceable. Whereas
at this location, lineations are weakly developed or subhorizontal
with sinistral kinematics, further east, between the villages of
Tonahuixtla and Totoltepec, the rocks possess a strong down-dip
mineral lineation and sigma-shaped tails on hornblende porphyroblasts suggest thrusting toward the south.
STOP 2-3 (W97.874964°°, N18.207481°°: Fig. 6)
Compositional/ textural banding in hornblende-bearing tonalites east of Tonahuixtla. Rocks at this stop have a mylonitic fabric and contain a conspicuous banding defined by a more or less
rhythmic variation in grain size and modal proportions of feldspar
and hornblende. Locally, these rocks exhibit gentle, ca. 2 m wavelength, fold-like structures resembling trough-banding characteristic of layered intrusions. These features indicate that the banding
may have a complex, multi-stage history of development, involving magma chamber, injection as well as tectonic processes.
10
Keppie et al.
97°54′0″W
320
Hbl Gabbro
97°48′0″W
Pb/206Pb
300
(95.7% conf, n=25)
290
207
18°16′0″N
97°50′0″W
310
306 ± 2 Ma
0.064
0.060
97°52′0″W
TuffZirc 206Pb/238U age
306 –1 +2 Ma
0.056
2-6
0.052
320
0.048
238
300
206
U/ Pb
19.6
20.0
2-4
290
2-5
2σ error ellipses
20.4
20.8
21.2
21.6
22.0
18°14′0″N
19.2
310
Contact
Contact, inferred
Strike-slip Fault
Normalfault
Thrustfault
San Jerónimo de Xayacatlán
2-1
Qtz Diorite
0.062
2-2
2-3
Pb/206Pb
280
(94.8% conf, n=22)
2-8
320
1
310
300
290
280
0.050
2-7
0.5
Totoltepec Pluton
granodiorite,
monzo-granite
trondhjemite
diorite, tonalite, felsic
and mafic dikes
hornblende gabbro,
hornblendite
207
18°12′0″N
0.058
0.054
0
300
290
Santo Domingo Tonahuíxtla
A
Cretaceous
Jurassic
Tecomate Formation
Amarillo Unit
Salada Unit
TuffZirc 206Pb/238U age
289 +1 –2 Ma
310
289 ± 2 Ma
Chichihualtepec
2
km
0.046
238
Scale 1:65,000
19
U/206Pb
20
2σ error ellipses
21
22
23
Frequency
50
B
Totoltepec Pluton
~306 Hbl Gabbro
0
Totoltepec Pluton
~289 Ma Qz Diorite
25
270
Pennsylvanian
PERMIAN
290
300
310
320
Mississippian
CARBONIFEROUS
Early Permian
n = 162
280
330
340
TT-81
Metapsammite
TT-82
Metapelite
TT-612
Metapsammite
TT-615
Granite veinlet
(detrital zircons)
350
80
C
5
Rhyodacite
Dacite
50
Basanite
Trachybasanite
Nephelinite
Subalkaline
Basalt
Alkali Basalt
Zr/TiO
40
289 Ma
Phonolite
quartz-rich granitoid
trondhjemite
plag-rich cumulate
tonalite
quartz diorite
hornblende diorite
hornblende gabbro
hornblendite
0
Nd
(t)
Trachyte
TrAn
Andesite
306 Ma
60
SiO [wt %]
Com/Pan
70
Totoltepec pluton
0.01
0.1
1
Tonahuixtla Member
metapelite
metapsammite
metaarkose
5
Asis amphibolites
Tecomate Fm. type area
10
0.001
Rel. Prob
Deplete
d
Mantle
D
Rhyolite
TEC-10
Granite cobble
Metacongl.
(Keppie et al., 2004)
t [Ga]
0
0.2
0.4
0.6
0.8
Oaxacan Complex
1.0
1.2
1.4
Figure 6. Stops 2-1 to 2-8: geological map of the Totoltepec pluton (after Kirsch et al., in press) showing field trip stops.
STOP 2-4 (W97.86816°°, N18.218361°°: Fig. 6)
Hornblende gabbro at the northern margin of the Totoltepec
pluton in contact with Jurassic redbeds. This outcrop is located
in one of three ca. 0.2–0.6 km2, fault-bounded, precursor (306 ±
2 Ma) gabbroic phase, which is distributed along the northern
and north-eastern margin of the pluton. Locally, these rocks are
intruded by intensely deformed felsic dikes. To the north, the
pluton is unconformably overlain by redbeds of inferred Jurassic
age, which sit steeply against the pluton buttress due to a subsequent period of normal faulting.
sional deformation. Rotated pebbles with asymmetric tails show
top-to-the-south shear, which is consistent with other kinematic
indicators in this area.
DAY 3
Gonzalo Galaz-Escanilla and J. Duncan Keppie
A High Pressure Zone within the Acatlán Complex:
Uppermost Devonian: Lower Carboniferous Subduction
and Extrusion under Extension during the Initial Stages of
Pangea Amalgamation
STOP 2-5 (W97.851633°°, N18.2581°°: Fig. 6)
Center of High Pressure Zone
Amarillo Unit (new name), SE of Santo Domingo Tianguistengo. This unit is characterized by medium- to high-grade
metasedimentary rocks locally intruded by amphibolite dikes.
Youngest detrital zircons from a garnet schist sample indicate a
maximum depositional age of 337 ± 4 Ma (Mississippian). The
amphibolite dikes exhibit a MORB-like geochemistry with εNd (i)
values of +5.2 to +7.6 and TDM model ages between 333 and
433 Ma. These features are very similar to those documented in
the Salada Unit (Morales-Gámez et al., 2008), on the western
side of the Totoltepec pluton.
Keppie, J.D., Nance, R.D., Dostal, J., Lee, J.K.W., and
Ortega-Rivera, A. 2011 Constraints on the subduction
erosion/extrusion cycle in the Paleozoic Acatlán
Complex of southern Mexico: geochemistry and
geochronology of the type Piaxtla Suite. Gondwana
Research, doi:10.1016/j.gr.2011.07.020
STOP 2-6 (W97.776016°°, N18.257016°°: Fig. 6)
Thrust contact between the Totoltepec pluton and the Tecomate Formation metasedimentary rocks. The exposed contact is
a low-angle brittle-ductile thrust. At another location, this thrust
is mylonitic and yielded a Middle Triassic 40Ar/39Ar age on muscovite. The contact is furthermore associated with a Fe-P-REE
deposit containing the mineral association magnetite, apatite,
barite, chlorite, quartz, chalcopyrite, and a cerium mineral. The
mineralization is confined to two discrete, elongated bodies of
~100 m length coinciding with strong aeromagnetic anomalies.
STOP 2-7 (W97.794857°°, N18.262697°°: Fig. 6)
S-C fabrics in the Tecomate Formation ~1 km south of the
margin of the Totoltepec pluton, indicating top-to-the-south
thrusting. Thermochronological data from this area as well as
other samples from the Tecomate Formation and Amarillo Unit
reveal a regionally significant tectonothermal event of midTriassic age.
STOP 2-8 (W97.892266°°, N18.190066°°: Fig. 6)
Pebble metaconglomerates of the Tecomate Formation near
Chichihualtepec. The pebbles from this outcrop, which are petrographically similar to the Totoltepec pluton trondhjemite, yielded
zircons with ages between 320 and 264 Ma (Keppie et al., 2004).
Morales-Gámez et al. (2009) conducted strain measurements in
these rocks, documenting prolate spheroids typical of transten-
11
ABSTRACT
The type high-pressure (HP) Piaxtla Suite in the Acatlán
Complex of southern Mexico consists of retrogressed eclogite
(amphibolite), megacrystic granitoids and high-grade metasedimentary rocks. Exhumation of these HP rocks has recently
been interpreted as the result of extrusion into the upper plate,
rather than by return flow up the subduction zone. Geochemical
analyses of the retrograde eclogites indicate that they have a
rift tholeiitic-transitional alkalic composition. These are closely
associated with a megacrystic meta-granitoid that has yielded
an intrusive age of 452 ± 6 Ma (concordant U-Pb zircon analyses) with inherited zircon populations at ca. 800–950 Ma and
1000–1200 Ma derived from the underlying basement, probably the Oaxacan Complex which borders the Acatlán Complex
to the east. The bimodal nature of these igneous rocks and their
close association with continentally-derived sedimentary rocks
is similar to most HP rocks in the Acatlán Complex derived
from a rifted passive margin. The youngest detrital zircon
population in a metapsammite sample yielded an U-Pb age of
365 ± 15 Ma with older analyses distributed along a chord with
an upper intercept of 1287 ± 29 Ma. The ca. 365 Ma age provides a maximum age for the time of deposition of this sample.
40
Ar/39Ar ages from the retrogressed eclogites provided hornblende plateau ages of 342 ± 2 Ma and 344 ± 2 Ma, whereas
muscovite from the granitoid and metapsammite yielded 334 ±
2 Ma plateau ages. These data constrain the subduction erosionextrusion cycle to ≤35 my during which the rocks were taken
to a depth of ca. 40 km at a rate of 2.7 km/my and back to the
surface at 2.4 km/my. Such exhumation rates are slower than
those in continent-continent collision zones, but similar to those
in the Iberia-Czech Variscan belt where tectonic interpretation
also suggests extrusion into the upper plate.
12
Keppie et al.
Western Boundary of High Pressure Zone: A HighPressure Folded Klippe Explaced during the Lower
Carboniferous at Tehuitzingo
Galaz E., Gonzalo, et al., in press. A high-pressure
folded klippe at Tehuizingo on the western margin of an
extrusion zone, Acatlán Complex, southern Mexico
ABSTRACT
The Acatlán Complex is divided into two blocks of lowgrade metamorphic rocks by a central belt of high-pressure (HP)
rocks, which at Tehuitzingo is composed of metabasites, serpentinite, granite and mica schist. 580–430 Ma detrital zircon ages
indicate that these rocks were deposited adjacent or very close
to the Gondwana supercontinent during the Early Paleozoic and
are more consistent with a development on the southern margin
of the Rheic Ocean rather than the Iapetus Ocean. These rocks
were then removed by a subduction-erosion to depths of ~50km,
reaching a metamorphic peak of ~16 kbar and 750 °C (eclogite
facies). The HP rocks underwent rapid extrusion during a major
Late Devonian-Pennsylvanian tectonothermal event indicated by
40
Ar/39Ar analyses, which yielded ages of ~373 Ma (hornblende
in metabasite) and of 328–317 Ma (muscovite in granite, mica
schist and metabasite) that indicate cooling through ~570 °C
and ~350 °C respectively, indicating a very high cooling rate of
~4.9–3.9 °C/m.y. During the extrusion process these rocks were
affected by retrogression to amphibolite-epidote and green schist
facies, and finally emplaced as a klippe on a greenschist facies
psammite-pelite unit that constitutes the western block of the
Acatlán Complex. Petrologic, deformational and geothermobarometric data suggest that west and east blocks belong to the
same terrane, indicating that a subduction-erosion process and
subsequent extrusion is more consistent with the genesis of the
HP central belt than a collisional event as has been proposed.
The P-T-t pattern of these HP rocks is consistent with subduction environments reported elsewhere in the world and suggests a
serpentinite extrusion channel on the western margin of Pangea.
Eastern Boundary of High Pressure Zone: A Listric
Normal Shear Zone Synchronous with Deposition of the
Uppermost Devonian–Lower Permian Patlanoaya Group
Keppie, J.D., Nance, R.D., Ramos-Arias, M.A., Lee, J.K.W.,
Dostal, J., Ortega-Rivera, AQ., and Murphy, J.B. 2010.
Late Paleozoic subduction and exhumation of CambroOrdovician passive margin and arc rocks in the northern
Acatlán Complex, southern Mexico: geochronological
constraints. Tectonophysics, v. 495, p. 213–229.
ABSTRACT
The origin and age of high pressure (HP) rocks is crucial
for paleogeographic reconstruction because they either mark an
oceanic suture or an extrusion zone within the upper plate. HP
rocks in the San Miguel Las Minas area in the northern part of
the complex has been inferred to be of early Paleozoic age and to
mark oceanic sutures. However, blueschists in the northern part
of the Acatlán Complex in southern Mexico have yielded Mississippian 40Ar/39Ar plateau ages of 344 ± 5 Ma for glaucophane
and 338 ± 3 Ma and 337 ± 2 Ma for muscovite. These ages are
slightly younger than recently published ages: a U-Pb zircon
age of 353 ± 1 Ma from associated eclogite, and a 347 ± 3 Ma
muscovite age from the tectonically overlying, greenschist facies
Las Minas Unit. Taken together, these data indicate rapid cooling
between 700° and 340°C in ca. 17 Myr. On the other hand, associated Ordovician Anacahuite Amphibolite cooled through ca.
500°C at 299 ± 6 Ma (40Ar/39Ar on hornblende) suggesting a second, Permian period of exhumation. Protoliths of the high grade
rocks include Cambrian-Ordovician, rift-passive margin, psammites, pelites, and tholeiitic dykes, an Ordovician mafic intrusion
(Anacahuite Amphibolite dated at 470 ± 10 Ma: U-Pb zircon)
and megacrystic granite (dated at 492 ± 12 Ma: U-Pb zircon),
and arc-related mafic rocks of unknown age. These upper plate
rocks are inferred to have been removed by subduction erosion
and taken to depths between 35 and 55 km where they underwent
blueschist-eclogite facies metamorphism. This was followed by
rapid extrusion along a channel bounded by an easterly dipping,
Mississippian, listric normal shear zone, and a thrust modified
by a Permian dextral fault. Rocks above and below the extrusion
zone are mainly Cambro-Ordovician rift-passive margin units,
but a small vestige of the arc preserved as dikes cutting rocks
lying unconformably beneath the fossiliferous latest DevonianLower Permian Patlanoaya Group. Since faunal data indicate that
Pangea had amalgamated by the Mississippian, at which time the
Acatlán Complex lay 1500–2000 km south of the Ouachita collisional orogen between Gondwana and Laurentia, it is inferred
that subduction and extrusion of the high pressure rocks occurred
on the active western margin of Pangea.
Ramos-Arias, M., Keppie, J.D., Ortega-Rivera, A., and Lee,
J.W.K. 2008. Extensional late Paleozoic deformation on
the western margin of Pangea, Patlanoaya area, Acatlán
Complex, southern Mexico. Tectonophysics, v. 448, p. 60–76.
ABSTRACT
New mapping in the northern part of the Paleozoic Acatlán
Complex (Patlanoaya area) records several ductile shear zones
and brittle faults with normal kinematics (previously thought to
be thrusts). These movement zones separate a variety of units
that pass structurally upwards from: (i) blueschist-eclogitic metamorphic rocks (Piaxtla Suite) and mylonitic megacrystic granites
(Columpio del Diablo granite ≡ Ordovician granites elsewhere in
the complex); (ii) a gently E-dipping, listric, normal shear zone
with top to the east kinematic indicators that formed under upper
greenschist to lower amphibolite conditions; (iii) the MiddleUpper Ordovician Las Minas quartzite (upper greenschist facies
psammites with minor interbedded pelites intruded by mafic dikes
and a leucogranite dike from the Columpio del Diablo granite)
unconformably overlain by the Otate meta-arenite (lower greenschist facies psammites and pelites): roughly temporal equivalents are the Middle-Upper Ordovician Mal Paso unit and prelatest Devonian Ojo de Agua unit (interbedded metasandstone and
slate, and metapelite and mafic minor intrusions, respectively)—
the Otate and Mal Paso units are intruded by the massive, 461 ± 2
Ma, Palo Liso megacrystic granite: decussate, contact metamorphic muscovite yielded a 40Ar/39Ar plateau age of 440 ± 4 Ma;
(iv) a steeply-moderately, E-dipping normal fault; (v) uppermost
Devonian-Lower Permian sedimentary rocks (Patlanoaya Group:
here elevated from formation status). The upward decrease in
metamorphic grade is paralleled by a decrease in the number
of penetrative fabrics, which varies from (i) three in the Piaxtla
Suite, through (ii) two in the Las Minas unit (E-trending sheath
folds deformed by NE-trending, subhorizontal folds with top to
the southeast asymmetry, both associated with a solution cleavage), (iii) one in the Otate, Mal Paso, and Ojo de Agua units
(steeply SE-dipping, NE-SW plunging, open-close folds), to (iv)
none in the Patlanoaya Group. 40Ar/39Ar analyses of muscovite
from the earliest cleavage in the Las Minas unit yielded a plateau
age of 347 ± 3 Ma and show low temperature ages of ~260 Ma.
Post-dating all of these structures and the Patlanoaya Group are
NE-plunging, subvertical folds and kink bands. An E-W, vertical
normal fault juxtaposes the low-grade rocks against the Anacahuite amphibolite that is cut by megacrystic granite sheets, both
of which were deformed by two penetrative fabrics. Amphibole
from this unit has yielded a 40Ar/39Ar plateau age of 299 ± 6 Ma,
which records cooling through ~490 °C and is probably related to
a Permo-Carboniferous reheating event during exhumation. The
extensional deformation is inferred to have started in the latest
Devonian (~360 Ma) during deposition of the basal Patlanoaya
Group, lasting through the rapid exhumation of the Piaxtla Suite
at ~350–340 Ma synchronous with cleavage development in the
Las Minas unit, deposition of the Patlanoaya Group with active
fault-related exhumation suggested by Mississippian and Early
Permian conglomerates (~340 and 300 Ma, respectively), and
continuing at least into the Middle Permian (≡ 260 Ma muscovite
ages). The continuity of Mid-Continent Mississippian fauna from
the USA to southern Mexico suggests that this extensional deformation occurred on the western margin of Pangea after closure
of the Rheic Ocean.
STOP 3-1 (N18°° 11.728′, W98°° 14.690′ to N18°° 11.652′,
W98°° 15.065′: Fig. 2)
Contact between a deformed, Ordovician megacrystic granitoid, a Tertiary dike, and the HP Piaxtla Suite at Piaxtla.
STOP 3-2 (UTM: 1405110/2023872: Fig. 7)
Thrust contact between Tehuitzingo serpentinite and
polydeformed psammitic-pelitic rocks at Solozuchitl near
Atopoltitlan.
13
The Piaxtla serpentinites are composed almost entirely of
secondary minerals. Decussate, acicular and fibrous crystals
serpentine aggregates make up 95% of the rock, magnetite, calcite, white mica and talc, and accessory chromite, clinochlore,
undulose quartz, amphibole and epidote. This serpentinite are
thrust over the low grade psammite-pelite unit along a gently
NW-dipping thrust (320/15°), on which there are striae that
plunge westwards (290/12°): associated recumbent folds, S-C
fabrics and thrust horses indicate thrusting toward the west. Cutting across this thrust zone are several N-S vertical faults with
subhorizontal striae.
The low grade psammite-pelite unit (498 ± 2 Ma, U-Pb detrital zircon; Galaz-Escanilla et al., in press) is composed mainly
of primary minerals such as quartz, feldspar and zircon (accessory), which suggests a medium-grained quartz-arenitic (0.25–
0.5 mm) and shaly (<0.06 mm grain size) protoliths respectively.
The equilibrium secondary mineralogy is composed of quartz,
albite (Ab99–100), Mg-Fe-chlorite (ripidolite type), phengite, epidote,
calcite and leucoxene, whose geothermobarometry indicated P-T
conditions of ~2.7 kbar and ~350 °C (greenschist facies; GalazEscanilla and Keppie, in press).
STOP 3-3 (UTM: 140571085/2023811: Fig. 7)
Serpentinite, amphibolite, metabasite, Ordovician granitic
and psammitic-pelitic rocks along the eastern margin of the
Tehuitzingo serpentinite at Tecolutla.
In Tecolutla area outcrop a HP unit (eclogitic facies) that
mainly consists of serpentinized harzburgite with small marginal
fault blocks of metabasite, metagranitoid (485 ± 3 Ma, U-Pb
zircon age: Galaz-Escanilla et al., in press) and mica schist (433 ±
3 Ma, U-Pb detrital zircon: Galaz-Escanilla et al., in press) juxtaposed by N-S structures. The serpentinized harzburgites contain
elliptical metabasite lenses up to several meters in size, which
have fine grained margins that may reflect an original intrusive
relationship. The long axes of the elliptical lenses are parallel to
the foliation indicating ductile deformation. On the other hand,
the high-grade metasediments have a composite foliation where
S1 is parallel to a second S-C foliation with the S2 planes subparallel to the border of the block and oriented ~128/27° (dip
direction/dip angle), and C2 planes oriented ~147/58°.
The HP unit is tectonically juxtaposed against a low grade
psammite-pelitic unit along N-S structures. This unit has a planar
fabric composed mainly of white mica and chlorite evidencing a
low-temperature (greenschist) ductile deformation.
The geothermobarometry suggests a common prograde
metamorphic history for the Tehuitzingo HP rocks: (a) a metamorphic peak eclogite facies of zoisite-amphibole, with a temperature of ~750 °C and a pressure of ~16 kbar; (b) retrogression to
amphibolite-epidote facies, with a temperature of ~472 °C and
variable pressures between ~7.1–3.4 kbar; (c) retrogression to greenschist facies with a temperature of ~360 °C and whose pressures
were not obtained (Galaz-Escanilla et al., in press). The Piaxtla
serpentinite contains three types of serpentine group minerals:
14
Keppie et al.
Figure 7. Stops 3-2 and 3-3: geological map, structural data, and section (after Galaz-Escanilla et al., in press).
Figure 8. Stops 3-4, 3-5, 3-6 and 3-7: geological map and section (after Keppie et al., 2010).
15
16
Keppie et al.
chrysotile, lizardite and antigorite. Based on the stability field
of the latter was estimated a P-T peak of ~550 °C and ~9 kbar
(González-Mancera, 2001), however, has been reported in subduction zones antigorite reaching ~720 °C and high pressures of
~20 kbar (Ulmer and Trommsdorff, 1995).
The geochemistry data of the eclogitic mafic rocks indicate
that these rocks have an arc affinity (author´s unpublished data).
The P-T-t pattern of these rocks is consistent with subduction
environments and serpentinite subduction channel exhumation
(e.g., Guillot et al. 2009), where the driving forces for exhumation are a combination of buoyancy and channel flow coupled
with underplating of slabs.
STOP 3-4 (N18°° 31.051′, W98°° 19.733′: Fig. 8)
Listric normal shear zone between megacrystic, Columpio
del Diablo granitoid and Ordovician Las Minas unit.
The Columpio del Diablo megacrystic granite (492 ± 12 Ma,
U-Pb zircon age: Keppie et al., 2010) consists of blastomylonitic
granite containing quartz, K-feldspar (perthitic orthoclase),
white mica, chlorite, epidote, and accessory opaque minerals.
The megacrystic granite is cut by thin leucogranite sheets that
consist mainly of quartz and potassium feldspar and are inferred
to be a late differentiates of the granite. Structurally, the granite varies from an L-tectonite to an L-S tectonite with kinematic
indicators, such as σ fabrics associated with the feldspars and
generally vertical, extensional, quartz-filled fractures within the
feldspars that indicate top-to-east movement along the contact
with the Las Minas Unit: a minor, brittle fault has been superimposed on the contact. The Las Minas unit consists predominantly of polydeformed, low-grade psammites interbedded with
thin pelitic phyllites, and intruded by many tholeiitic mafic dikes
and sills (Keppie et al., 2008). The psammites consist mainly of
quartz with minor muscovite, chlorite, and K-feldspar, and accessory zircon, whereas the phyllites are composed of muscovite,
chlorite, quartz, and opaque minerals. The youngest concordant
detrital zircon is dated at 496 ± 25 Ma (Keppie et al., 2008) The
mafic intrusions contain amphibole (tremolite-actinolite), chlorite, epidote, quartz, plagioclase, muscovite, and accessory calcite, and opaque minerals. 40Ar/39Ar analyses of muscovite from
the earliest cleavage in the Las Minas unit yielded a plateau age
of 347 ± 3 Ma (Mississippian) and show low temperature ages
of ~260 Ma.
STOP 3-5 (N18°° 30.351′, W98°° 17.57′: Fig. 8)
The Cerro Puntiagudo Formation of Strunian age (latest
Devonian) is 63 m thick and consists of shale, sandstone, and
limestone. It is overlain by conglomerates of the Potrerillo
Formation (124 m thick) that consists of red sandstone with
Oseagean fossils and conglomerate with large K-feldspar clasts:
these clasts are inferred to have been derived from the nearby
megacrystic granitoids. The Cerro Puntiagudo Formation rests
unconformably upon the Ojo de Agua unit, which consists of
finely bedded, black pelitic rocks intruded by green, fine grained,
mafic dikes with an arc-related chemistry. These latter rocks are
deformed by isoclinal, upright-steeply inclined, NE- and SEtrending, subhorizontal folds. The youngest detrital zircons in
this unit are 466 ± 25 Ma (Keppie et al., 2008), abd 471 ± 9 Ma
(Keppie et al., 2010).
STOP 3-6 (N18°° 30.66′ W98°° 17.78′: Fig. 8)
The La Junta Formation is a 126 m thick shale unit containing Missourian fossils; the Tepazulco Formation (193 m thick) is
made up of interbedded limestone, shale, and sandstone and contains Virgilian-Missourian fossils. An Ordovician plug is faulted
against the Patlanoaya Group at this locality.
STOP 3-7 (N18°°31′, W°°16.79′: Fig. 8)
The Lower Permian La Mesa, La Cuesta and La Cueva Formations consist of a conglomerate (45 m thick) and calcareous
sandstone unit containing Wolfcampian fossils; interbedded shale
and limestone with mid-Wolfcampian to middle Leonardian fossils; and sandstone (>280 m thick) containing late Leonardian
fossils at its base.
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Printed in the U.S.A.
5
RESUMEN Y CONCLUSIÓN
Este trabajo documenta el desarrollo de un sistema de arco CarboníferoPérmico a lo largo del margen occidental de Pangea junto a una zona de
subducción del océano Paleo-Pacífico. Se proporciona información detallada sobre la relación entre el plutonismo, la formación de cuencas y la deformación a escala regional en un orógeno periférico. Las principales conclusiones son las siguientes:
a. La cartografía geológica detallada de la zona en combinación con los
datos de la geocronología U-Pb de circones da como resultado la modificación de la distribución espacial y las relaciones de contacto de las
unidades litotectónicas previamente mapeadas en el área de estudio.
Los contactos externos entre el plutón Totoltepec y las rocas circundantes son o no conformables, o son tectónicos (es decir, ninguna de
las relaciones de contacto originales son preservadas). Sin embargo, la
edad de diques graníticos delgados que ocurren dentro de la Formación Tecomate sugieren que pueden ser comagmáticos con el plutón
Totoltepec, lo que implica una relación originalmente intrusiva entre
el plutón y la Formación Tecomate.
b. Rocas clásticas al suroeste del plutón Totoltepec que fueron asignados
originalmente a la Formación Cosoltepec contienen circones detríticos de edad Pérmico y por lo tanto se consideran equivalentes a la
Formación Tecomate. Esta interpretación es coherente con la presencia de metaconglomerados y mármoles en esta parte de la zona de
campo. Además, en la parte oriental del área de estudio se identifica
una unidad metamórfica de grado medio y edad Misisipiense (artículo en preparación), que consiste en cuarcitas y esquistos de granate
con escasos diques de anfibolita; esto limita la distribución espacial
de la unidad previamente mapeada como la Formación Tecomate. La
unidad Misisipiense está en contacto de falla con el plutón Totoltepec, cabalgando en dirección sur sobre la Formación Tecomate y está
sobreyacida por capas rojas del Jurásico hacia el norte. Con base en
datos isotópicos y geoquímicos, las rocas de esta unidad Misisipiense
se pueden correlacionar con las de la Unidad Salada del Carbonífero (Morales-Gámez et al., 2008) que afloran en el lado occidental del
plutón Totoltepec.
c. Circones detríticos extraídos de rocas de la Formación Tecomate en el
área de estudio en combinación con datos publicados de 40 Ar/39 Ar
proporcionan límites temporales de depositación a alrededor de 300
Ma en un nivel estratigrafico, y a entre 288 ± 3 Ma y 263 ± 3 Ma en
76
otro. Estos datos coinciden con la edad bioestratigráficamente determinada en el área tipo de la Formación Tecomate (Keppie et al., 2004b)
e indican que la formación, como se define actualmente de manera
colectiva se extiende desde el Pensilvánico medio hasta el Pérmico
Inferior, pero puede haber sido depositada en distintas sub-cuencas
de diferentes edades. Una de las muestras analizadas, que proviene
de cerca de la base estratigráfica de la Formación Tecomate, produjo
solamente circones de edad Proterozoica, lo cual sugiere que esta parte de la unidad fue depositada cuando fuentes ígneas paleozoicas no
estaban expuestas o no fueron muestreadas por el sistema de drenaje local. La última explicación también podría aclarar la discrepancia
entre las edades de las poblaciones más jóvenes de circones detríticos de la zona de estudio y el área tipo de la Formación Tecomate
(Sánchez-Zavala et al., 2004), respectivamente.
d. La secuencia intrusiva del plutón Totoltepec se establece mediante la
documentación del rango composicional, los contactos internos y la
edad de las fases magmáticas; esto se basa en el análisis petrográfico
y trabajo de campo detallado, complementado por la geocronología de
U-Pb y 40 Ar/39 Ar. Estos datos sugieren que el plutón es una intrusión
compuesta, formado por (i) tres cuerpos discretos, alargados e intensamente fallados de 306 ± 2 Ma, que consisten en gabro hornblendico
y hornblendita, aflorando a lo largo del margen norte del plutón; (ii)
trondhjemita de 287 ± 2 Ma, la litología predominante del plutón, localmente mostrando una mayor abundancia de biotita o plagioclasa y
transformándose a una composición granodiorítica y monzogranítica
cerca del margen norte; y, (iii) cuerpos intrusivos de tonalita y diorita
hornblendica junto con diques félsicos que se presentan en el parte
sur del plutón, los cuales fueron emplazados secuencialmente entre
289 ± 2 y 283 ± 1 Ma.
e. Tanto la fase marginal (gabróica) como la fase principal (trondhjemitatonalita-diorítica) del plutón Totoltepec muestran una afinidad geoquímica toleítica a calco-alcalina, típico de magmas asociados con
subducción. Estos datos proporcionan evidencia de un manto litosférico subcontinental hidratado por fluidos de subducción ya en 306
Ma aproximadamente, mucho antes de lo que varios estudios proponen. Datos isotópicos de Sm-Nd indican una relación genética de
asimilación-cristalización fraccionada (AFM) por cantidades menores
entre la fase marginal y principal del plutón. Plutones coetáneos del
arco Carbonífero–Pérmico en el sur de México y Guatemala son más
félsicas y más alcalinas en composición, muestran patrones de tierras
raras más diferenciados y tienen una firma isotópica de Sm-Nd menos
radiogénico; esto indica una mayor contaminación cortical en comparación con el plutón Totoltepec y sugiere que el plutón fue emplazado
en una parte más primitiva, más cercana a la trinchera del arco y/o a
lo largo de una falla que facilitó su ascenso.
77
f. Las rocas de la Formación Tecomate en el área de estudio son derivadas del edificio del arco regional y de plutones epizonales expuestos
durante el Carbonífero y el Pérmico Inferior, lo cual es indicado por:
(i) la ocurrencia de estratos intercalados de rocas volcánicas y clásticas que son derivados de un arco; (ii) la inmadurez composicional y
textural de los sedimentos; (iii) la firma geoquímica de arco de las
rocas clásticas; (iv) composiciones isotópicas de Sm-Nd relativamente
radiogénicos que sugieren un componente de procedencia juvenil; y,
(v) el predominio de circones detríticos del Carbonífero–Pérmico procedentes de una fuente ígnea. Por lo tanto, circones detríticos de la
Formación Tecomate complementan el registro detrítico fragmentado
de la actividad del arco magmático regional en el sur de México. En
conjunto con otras rocas ígneas y sedimentarias relacionadas con el
arco en México y Guatemala, cuya edad también está bien definida
por bioestratigrafía o por geocronología U-Pb, los datos sugieren que
la actividad de arco ya había iniciado en el Misisípico en los bloques
más al sur y probablemente no fue establecido en los terrenos del
norte de México hasta el Pérmico Inferior.
g. La historia estructural para la fase principal del plutón Totoltepec de
aproximadamente 289–287 Ma, como se infiere a partir de la termobarometría Al-en-hornblenda y la geocronología 40 Ar/39 Ar involucró
el emplazamiento de magma en niveles medianos de la corteza (unos
20 km de profundidad) y un levantamiento rápido hasta aproximadamente 11 km en 4 ± 2 Ma. La forma superficial elíptica del plutón,
una progresión de una fábrica de flujo magmático a una fábrica de
estado sólido de baja temperatura, así como el paralelismo entre las
foliaciones de temperaturas distintas indican que el emplazamiento
de la fase principal del plutón fue controlada tectónicamente. La intrusión principal contiene una foliación subvertical paralela al eje largo del plutón, y una lineación mineral que varia desde subhorizontal
con cinemática sinistral hasta muy inclinada con indicadores de cabalgamiento de vergencia sur. La variación en la orientación y el grado
de deformación manifestado por las diferentes poblaciones de diques
sugieren que los diques fueron emplazados secuencialmente y fueron
sometidos a diferentes grados de rotación en sentido horario.
h. En el marco del arco regional que está dominado por cizallamiento
dextral a lo largo de fallas N–S, el emplazamiento del plutón Totoltepec se infiere haber tenido lugar a lo largo de un sistema de fallas
transversales al arco de extensión oblicua y dirección NE en un régimen general de transtensión. El magmatismo puede haber cesado
en la zona cuando una parte del cizallamiento dextral de la falla delimitante del oeste fue trasladado a la falla delimitante del este, que
culminó en cabalgamiento cerca del margen sur del plutón. Por último, como parte de un evento importante de deformación regional
en el Triásico Medio a Tardío, que se registra en las rocas tanto de
78
la Formación Tecomate como de la unidad Misisipiense sin nombre
(artículo en preparación), el plutón fue cabalgado sobre las rocas metasedimentarias de la Formación Tecomate.
i. Este estudio documenta la evolución geodinámica de un arco continental del Paleozoico tardío en el Complejo Acatlán. Los datos sugieren subducción oblicua de litosfera oceánica hacia el este, por debajo
del terreno Mixteco, que produjo el desarrollo de fallas laterales N–S
paralelas a la trinchera y fallas antitéticas de orientación NE que promovió el plutonismo y dio lugar a la formación de múltiples cuencas
pull-apart. Esta situación tectónica es más compatible con una ubicación paleogeográfica del terreno Mixteco en el margen de Pangea que
una posición en el Golfo de México, varios miles de kilómetros hacia
el interior, o incluso una ubicación frente al noreste de Canadá.
79
A
MÉTODOS ANALÍTICOS
A.1 y A.2: Material suplementario publicado en línea como parte del artículo: Kirsch, M., Keppie, J.D., Murphy, J.B., y Solari, L.A., 2012, Permian–
Carboniferous arc magmatism and basin evolution along the western margin of Pangea: geochemical and geochronological evidence from the eastern
Acatlán Complex, southern Mexico: Geological Society of America Bulletin,
en prensa, doi: 10.1130/B30649.1.
a.1
geocronología u-pb
About 70 grains for igneous analyses and 150 grains in case of detrital
zircon analyses were handpicked and mounted on double-sided adhesive
tape. To avoid introducing bias into sample preparation, no selection was
made on the basis of optical and physical characteristics. The mount was
then cast in epoxy resin, ground with sandpaper to expose the crystals and
polished. Cathodoluminescence imaging was performed using an ELM-3R
luminoscope, to reveal internal zoning of the zircons, helping with the spot
selection and aiding the geological age interpretation. The isotopic analyses were performed with a Resolution LPX220 ArF Excimer laser ablation
system coupled to a Thermo Xii series quadrupole ICP-MS (Solari et al.,
2010) installed in the Laboratorio de Estudios Isotópicos (LEI), Centro de
Geociencias, UNAM. A 34 µm spot was used for all the analyses performed
during the current work. Repeated standard measurements of the Plešovice
standard zircon, (Sláma et al., 2008) enabled mass-bias correction, as well as
downhole and drift fractionation corrections. The analytical routine includes a standard glass (normally NIST 610 is analyzed), 5 standard zircons,
5 unknown zircons, and then 1 standard zircon every 5 unknowns, ending
with 2 standard zircons. The same analytical protocol is employed (timing,
energy density, laser frequency, spot size) for all the analyses, both standard and unknowns. NIST standard glass analyses are used to recalculate
the zircons trace element concentrations. Time-resolved analyses are then
reduced off-line using an in-house developed sofware written in R (Solari
y Tanner, 2011), and the output is then imported into Excel, where the concordia as well as age-error calculations are obtained using Isoplot v. 3.70
(Ludwig, 2008), while the probability density distribution and histogram
plots are produced using AgeDisplay (Sircombe, 2004). During the analytical sessions in which the data presented in this paper were measured at LEI,
UNAM, the observed uncertainties (1σ relative standard deviation) on the
206 Pb/238 U, 207 Pb/206 Pb and 208 Pb/232 Th ratios measured on the Plešovice standard zircon were 0.6, 0.9 and 1.1 % respectively. Those errors are
quadratically added to the quoted uncertainties observed on the measured
80
A.2 geoquímica
isotopic ratios of the unknown zircons. This last factor takes into account
the heterogeneities of the natural standard zircons. 204 Pb, which would be
used to correct for initial common Pb, is not measured because its tiny signal is swamped by 204 Hg, normally present in the He carrier gas. Common
Pb is thus evaluated using the 207 Pb/206 Pb ratio, carefully graphing all the
analyses on Tera y Wasserburg (1972) diagrams. Correction, if needed, is
then performed with the algebraic method of Andersen (2002).
a.2
geoquímica
Major and certain trace elements (V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr,
Nb, Ba, La, Pb, Th, U, Ce, Nd, Cs) were determined by X-ray fluorescence spectrometry (XRF) at the Regional Geochemical Centre at Saint Mary’s
University, Nova Scotia. Precision and accuracy are generally within 5 % for
most major elements, and within 5–10 % for minor and trace elements. Details of the analytical procedures are given in Dostal et al. (1986, 1994). REEs
and selected trace elements were analyzed by inductively coupled plasma
mass spectrometry (ICP-MS) at Memorial University, Newfoundland. The
accuracy and precision of these data are better than 10 %; the analytical procedure is detailed in Longerich et al. (1990). Sm-Nd isotopic analyses were
performed at the Atlantic Universities Regional Isotopic Facility (AURIF),
Memorial University, Newfoundland. Sm and Nd concentrations as well as
isotopic compositions and ratios were measured by isotope dilution thermal
ionization mass spectrometry (ID-TIMS) after chemical separation of Nd
and Sm by ion exchange chromatography (see Kerr et al., 1995). Instrumental mass fractionation of Nd isotopes is corrected relative to 146 Nd/144 Nd
= 0.7219 (O’Nions et al., 1977) using a Raleigh fractionation law. External
precision is assessed by replicate analyses of the JNdi-1 standard (Tanaka et al., 2000). The difference between the certified value (143 Nd/144 Nd =
0.512115) and the mean (0.512101 ± 0.000008 [n = 45]) is added to the measured value for 143 Nd/144 Nd after it has been spike-corrected. Errors quoted
in Table 1 represent standard errors of individual 143Nd/144Nd measurements at the 95 % confidence level. Nd parameters were calculated relative
to 143 Nd/144 Nd = 0.512638 for CHUR (Goldstein et al., 1984). For initial values, 147 Sm/144 Nd = 0.1967 (Jacobsen y Wasserburg, 1980) and λ147 Sm =
6.54 x 10−12 yr−1 (Steiger y Jäger, 1977) were used. Depleted mantle model
ages (TDM) are calculated in two ways: TDM(1) using the depleted mantle
model of DePaolo (1981, 1988), and TDM(2) which assumes a linear evolution of the depleted mantle between a value of +10 (present day) and 0 at
4.5 Ga (Goldstein et al., 1984). TDM(1) values are quoted in the text.
a.3
geocronología
40 ar- 39 ar
Los separados de minerales y los monitores de flujo (estándares) fueron
envueltos en papel de aluminio y apilados verticalmente en una cápsula de
irradiación 8.5 cm de largo y 2.0 cm de diámetro. Esta se irradió con neutro-
81
A.3 geocronología
40 ar- 39 ar
nes rápidos en la posición 5C del Reactor Nuclear de McMaster (Hamilton,
Ontario) para una duración de 24 h (a 2.5 MWh). Los paquetes de monitores
de flujo se encuentran a intervalos de aprox. 1 cm a lo largo del contenedor
de irradiación y valores de J para las muestras individuales se determinaron
por interpolación polinómica de segundo orden entre los análisis repetidos
para cada posición del monitor en la cápsula. Típicamente, valores de J varían menos que 10 % a lo largo de la cápsula. No se controlan gradientes
horizontales de flujo ya que se consideran ser de menor importancia en el
núcleo del reactor.
Para la fusión total de los monitores y el calentamiento por pasos utilizando un láser, las muestras se colocan en un portamuestras de cobre, por
debajo del viewport ZnS de una celda de acero inoxidable conectado a un
sistema de la purificación del vacío ultra-alto. Para el calentamiento por pasos se utilizó un láser New Wave Research MIR 10-30 de CO2 con potencias
de hasta 30W y una lente de facetas. Los periodos de calefacción son aprox.
3 minutos por cada incremento de energía (2 % a 20 %; diámetro del haz 3.8
mm). El gas liberado, después de la purificación mediante un getter SAES
C50 (unos 5 minutos), es conducido a un espectrómetro de masas MAP 216
con una fuente Bäur Signer y un multiplicador de electrones (ajustado a
una ganancia de 100 por el detector de copa de Faraday). Posteriormente,
los análisis rutinarios del blanco se restan de las fracciones de gas de las
muestras. Los blancos de extracción son típicamente <10 × 10−13 , <0.5 ×
10−13 , <0.5 × 10−13 , y <0.5 × 10−13 cm−3 STP para las masas 40, 39, 37, y
36, respectivamente.
Mediciones de los picos de los isótopos de argón son extrapolados al
tiempo cero, normalizados a la relación 40 Ar/36 Ar atmosférica (295.5) utilizando los valores obtenidos para el argón atmosférico, y corregidos a 40 Ar
producido por potasio, 39 Ar y 36 Ar por calcio, y a 36 Ar producido por cloro
Roddick (1983). Las fechas y los errores se calcularon utilizando el procedimiento de Dalrymple et al. (1981) y las constantes de Steiger y Jäger (1977).
La meseta e la inversa correlación de las fechas isotópicas se calcularon utilizando ISOPLOT v. 3.60 (Ludwig, 2008). Una meseta se define aquí como
3 o más etapas contiguas que contienen >50 % del 39 Ar liberado, con una
probabilidad de ajuste >0.01 y un promedio ponderado de las desviaciones
cuadráticas <2. Si los pasos contiguos contienen <50 % del 39 Ar liberado,
se conoce como un segmento de meseta.
Los errores citados en la tabla y en los espectros de edad representan la
precisión analítica a 2σ, suponiendo que los errores en las edades de los
monitores de flujo son cero. Esto es adecuado para comparar la variación
dentro del espectro y determinar cuáles pasos forman una meseta (por ejemplo, McDougall y Harrison (1988), p. 89). Una estimación conservadora de
este error en el valor de J es de 0.5 %; este se puede agregar para la comparación entre muestras. Las fechas están referenciadas a hornblenda Hb3Gr
de 1072 Ma (Turner et al., 1971; Roddick, 1983).
82
B
TA B L A S G E O C R O N O L O G Í A U - P B
Material suplementario publicado en línea como parte del artículo: Kirsch,
M., Keppie, J.D., Murphy, J.B., y Solari, L.A., 2012, Permian–Carboniferous
arc magmatism and basin evolution along the western margin of Pangea:
geochemical and geochronological evidence from the eastern Acatlán Complex, southern Mexico: Geological Society of America Bulletin, en prensa,
doi: 10.1130/B30649.1.
Tabla 1: Description of samples for LA-ICP-MS U-Pb geochronology from the Totoltepec area, Acatlán Complex.
Sample
Latitude
Longitude
(◦ N)
(◦ W)
Rocktype
Mineralogy
Primary
Secondary
Age
Accessory
(Ma)*
Permian granitoids (Totoltepec pluton)
TT-72
18.2581000
97.85163333
Hbl gabbro
Hbl+Pl
Ep+Chl
Ap+Zrn+Op
306±2
TT-76b
18.2286500
97.86343333
Qz diorite
Pl+Qz+Ms
Chl
Ap+Zrn+Op
289±2
Permian low-grade metasedimentary rocks
TT-81
18.25146667
97.78271667
Metaps.
Qz+Kfs+Ms
Chl
Zrn+Op
288±3
TT-82
18.25058333
97.78281667
Metapel.
Qz+Ms
Chl+Ser
Zrn+Op
299±3
TT-612
18.1912838
97.898541
Metaps.
Qz+Kfs+Ms
Chl
Zrn+Op
303±3
TT-486A
18.2840884
97.9111441
Metaps.
Qz+Kfs+Ms
Chl
Zrn+Op
1005±17
Zrn+Op
298±3
Thin dikes intruding Carboniferous–Permian low-grade metasedimentary rocks
TT-615
18.1908117
-97.8990905
Granitoid
Qz+Pl+Ms
Abbreviations: Qz–quartz, Kfs–K-feldspar, Pl–plagioclase, Hbl–hornblende, Bt–biotite, Ms–
muscovite, Ser–sericite, Ep–epidote, Chl–chlorite, Ap–apatite, Grt-garnet, Tnt–titanite, Zrn–
zircon, Op–opaque minerals
* LA-ICP-MS U-Pb zircon ages representing the age of crystallization in igneous rocks and
an average of the youngest detrital zircon cluster in metasedimentary rocks, respectively
(see text for details).
83
0.49
0.54
0.39
0.48
0.61
0.60
0.42
0.42
0.54
0.52
0.55
0.51
0.55
0.53
0.55
0.45
0.53
0.43
Zrc_31_043
Zrc_19_029
Zrc_21_032
Zrc_24_035
Zrc_02_009
Zrc_09_017
Zrc_05_012
Zrc_10_018
Zrc_17_027
Zrc_01_008
Zrc_03_010
Zrc_38_050
Zrc_04_011
Zrc_35_046
Zrc_32_044
Zrc_34_045
Zrc_07_015
Zrc_08_016
Spot name Th/U
0.05333
0.05365
0.05209
0.05425
0.05213
0.05386
0.05173
0.05494
0.05345
0.05326
0.05588
0.05769
0.05493
0.05220
0.05304
0.05306
0.05332
0.05891
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
2.91 0.35595 2.98 0.04856 0.68 0.22
2.11 0.35874 2.23 0.04863 0.74 0.33
2.30 0.34687 2.41 0.04841 0.70 0.29
2.19 0.36186 2.30 0.04846 0.68 0.31
2.09 0.34737 2.19 0.04836 0.62 0.30
2.10 0.35898 2.22 0.04831 0.72 0.33
2.20 0.34235 2.26 0.04810 0.52 0.22
2.29 0.36274 2.41 0.04806 0.73 0.31
2.51 0.35438 2.60 0.04806 0.71 0.26
2.29 0.35147 2.39 0.04796 0.65 0.29
2.70 0.36909 2.79 0.04795 0.71 0.25
2.89 0.38116 3.01 0.04804 0.81 0.28
2.60 0.36184 2.69 0.04783 0.71 0.26
2.30 0.34437 2.41 0.04788 0.73 0.30
2.39 0.34732 2.48 0.04757 0.61 0.26
3.20 0.34550 3.45 0.04744 1.31 0.37
2.10 0.34853 2.18 0.04748 0.59 0.27
2.21 0.34265 2.34 0.04224 0.80 0.33
1σ
Isotopic ratios (errors in %)
306
306
305
305
304
304
303
303
303
302
302
302
301
301
300
299
299
267
206 Pb/238 U
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
4
2
2
1σ
309
311
302
314
303
311
299
314
308
306
319
328
314
300
303
301
304
299
207 Pb/235 U
8
6
6
6
6
6
6
7
7
6
8
8
7
6
6
9
6
6
1σ
64
46
51
48
47
46
49
50
54
50
58
62
56
50
53
71
46
47
306
306
305
305
304
304
303
303
303
302
302
302
301
301
300
299
299
267
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
4
2
2
1σ Best age 1σ
Continued on next page...
343
356
289
381
291
365
273
410
348
340
448
518
409
294
331
331
342
564
207 Pb/206 U
Ages (Ma)
Tabla 2: LA-ICP-MS U-Pb isotopic data for Totoltepec pluton hornblende gabbro.
84
0.50
0.46
0.40
0.61
0.55
0.47
0.40
0.49
0.37
0.41
0.42
0.49
0.30
0.30
0.48
0.59
0.34
Zrc_12_021
Zrc_16_026
Zrc_22_033
Zrc_27_038
Zrc_13_022
Zrc_28_039
Zrc_29_040
Zrc_37_049
Zrc_39_051
Zrc_20_030
Zrc_30_041
Zrc_36_048
Zrc_06_014
Zrc_26_037
Zrc_41_053
Zrc_11_020
Zrc_15_024
Spot name Th/U
0.05529
0.05456
0.05327
0.05695
0.05841
0.05287
0.05283
0.05441
0.05341
0.05334
0.05121
0.05196
0.05418
0.05430
0.05211
0.05491
0.05411
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
3.60 0.37543 3.70 0.04944 0.87 0.23
2.20 0.37171 2.30 0.04950 0.69 0.30
2.59 0.35962 2.72 0.04925 0.79 0.30
3.11 0.38595 3.19 0.04931 0.73 0.22
3.41 0.39474 3.52 0.04920 0.91 0.25
2.10 0.35770 2.22 0.04917 0.71 0.32
2.31 0.35707 2.38 0.04914 0.61 0.24
3.11 0.36635 3.19 0.04910 0.75 0.23
3.30 0.35617 3.86 0.04891 2.00 0.52
2.10 0.35955 2.21 0.04892 0.67 0.31
2.89 0.34582 2.98 0.04894 0.65 0.24
3.00 0.35012 3.11 0.04889 0.82 0.26
2.49 0.36420 2.59 0.04872 0.70 0.28
2.39 0.36295 2.48 0.04854 0.64 0.26
2.71 0.34804 2.78 0.04856 0.66 0.23
2.60 0.36824 2.70 0.04864 0.74 0.26
2.20 0.36172 2.29 0.04861 0.62 0.27
1σ
311
311
310
310
310
309
309
309
308
308
308
308
307
306
306
306
306
206 Pb/238 U
3
2
2
2
3
2
2
2
6
2
2
2
2
2
2
2
2
1σ
324
321
312
331
338
310
310
317
309
312
302
305
315
314
303
318
313
207 Pb/235 U
10
6
7
9
10
6
6
9
10
6
8
8
7
7
7
7
6
1σ
424
394
340
490
545
323
322
388
346
343
250
284
379
384
290
409
376
207 Pb/206 U
Ages (Ma)
Tabla 2: LA-ICP-MS U-Pb isotopic data for Totoltepec pluton hornblende gabbro.
78
48
57
67
72
47
51
68
73
46
65
67
54
53
60
56
48
311
311
310
310
310
309
309
309
308
308
308
308
307
306
306
306
306
3
2
2
2
3
2
2
2
6
2
2
2
2
2
2
2
2
1σ Best age 1σ
85
0.29
0.32
0.53
0.39
0.35
Zrc_69_089
Zrc_78_100
Zrc_72_093
0.28
Zrc_46_062
Zrc_49_065
0.72
Zrc_42_057
Zrc_64_083
0.35
0.62
Zrc_70_090
0.52
Zrc_66_086
Zrc_74_095
0.29
0.42
0.27
Zrc_76_098
Zrc_79_101
0.63
Zrc_47_063
Zrc_59_077
1.19
0.27
Zrc_52_069
0.65
Zrc_81_104
Zrc_57_075
0.01
Zrc_56_074
Spot name Th/U
0.05170
0.05412
0.05337
0.05426
0.04966
0.05258
0.05444
0.05159
0.05270
0.05334
0.05376
0.05452
0.05301
0.05201
0.05294
0.05239
0.05271
0.05190
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
1.80 0.32825 1.86 0.04599 0.50 0.26
1.90 0.34121 2.00 0.04583 0.63 0.31
1.50 0.33761 1.61 0.04587 0.59 0.36
1.81 0.34365 1.91 0.04591 0.63 0.32
2.50 0.31351 2.60 0.04582 0.70 0.27
2.21 0.33114 2.30 0.04581 0.68 0.29
1.60 0.34365 1.69 0.04584 0.55 0.33
1.61 0.32509 1.69 0.04572 0.52 0.30
1.71 0.33238 1.78 0.04570 0.50 0.27
1.59 0.33561 1.70 0.04560 0.57 0.35
1.90 0.33778 2.00 0.04556 0.61 0.31
2.49 0.34052 2.57 0.04532 0.60 0.24
2.21 0.33200 2.28 0.04542 0.62 0.26
1.50 0.32588 1.57 0.04543 0.46 0.30
1.91 0.32939 1.99 0.04517 0.60 0.28
1.20 0.32621 1.33 0.04515 0.58 0.42
1.90 0.32368 2.15 0.04461 1.01 0.47
1.43 0.31578 1.59 0.04413 0.48 0.40
1σ
290
289
289
289
289
289
289
288
288
287
287
286
286
286
285
285
281
278
206 Pb/238 U
1
2
2
2
2
2
2
1
1
2
2
2
2
1
2
2
3
1
1σ
288
298
295
300
277
290
300
286
291
294
295
298
291
286
289
287
285
279
207 Pb/235 U
5
5
4
5
6
6
4
4
4
4
5
7
6
4
5
3
5
4
1σ
41
43
34
38
54
47
33
37
39
34
40
56
50
32
40
26
43
33
290
289
289
289
289
289
289
288
288
287
287
286
286
286
285
285
281
278
1
2
2
2
2
2
2
1
1
2
2
2
2
1
2
2
3
1
1σ Best age 1σ
272
376
345
382
179
311
389
267
316
343
361
393
329
286
326
302
316
281
207 Pb/206 U
Ages (Ma)
Tabla 3: LA-ICP-MS U-Pb isotopic data for Totoltepec pluton quartz diorite.
86
0.27
0.40
0.33
0.27
0.25
Zrc_71_092
Zrc_51_068
Zrc_62_081
0.40
Zrc_53_070
Zrc_54_071
0.35
Zrc_50_066
Zrc_43_058
0.52
0.26
Zrc_77_099
0.38
Zrc_75_096
Zrc_80_102
0.61
0.40
0.33
Zrc_67_087
Zrc_44_059
0.62
Zrc_58_076
Zrc_68_088
0.34
0.56
Zrc_55_072
0.32
Zrc_48_064
Zrc_65_084
0.59
Zrc_82_105
Spot name Th/U
0.05176
0.05225
0.05291
0.05167
0.05076
0.05174
0.05305
0.05278
0.05205
0.05314
0.05266
0.05245
0.05296
0.05238
0.05252
0.05302
0.05229
0.05244
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
6.39 0.34109 6.70 0.04780 0.90 0.24
2.79 0.34302 2.90 0.04764 0.76 0.27
2.10 0.34411 2.24 0.04720 0.76 0.35
1.99 0.33458 2.10 0.04702 0.64 0.32
2.01 0.32714 2.12 0.04680 0.68 0.31
2.20 0.33470 2.28 0.04685 0.60 0.26
2.51 0.34103 2.61 0.04681 0.75 0.28
2.10 0.33938 2.20 0.04665 0.64 0.29
1.50 0.33415 1.57 0.04653 0.47 0.31
1.90 0.34070 1.97 0.04651 0.52 0.26
1.90 0.33861 2.00 0.04658 0.62 0.32
1.51 0.33597 1.60 0.04644 0.56 0.34
1.70 0.33881 1.79 0.04636 0.56 0.31
1.39 0.33411 1.51 0.04627 0.56 0.39
1.81 0.33404 1.93 0.04620 0.69 0.35
1.79 0.33711 1.90 0.04610 0.61 0.34
1.80 0.33269 1.93 0.04616 0.69 0.37
1.39 0.33359 1.48 0.04606 0.50 0.35
1σ
301
300
297
296
295
295
295
294
293
293
293
293
292
292
291
291
291
290
206 Pb/238 U
3
2
2
2
2
2
2
2
1
1
2
2
2
2
2
2
2
1
1σ
298
299
300
293
287
293
298
297
293
298
296
294
296
293
293
295
292
292
207 Pb/235 U
17
8
6
5
5
6
7
6
4
5
5
4
5
4
5
5
5
4
1σ
136
60
47
43
43
47
53
47
34
43
43
32
38
30
38
38
38
31
301
300
297
296
295
295
295
294
293
293
293
293
292
292
291
291
291
290
3
2
2
2
2
2
2
2
1
1
2
2
2
2
2
2
2
1
1σ Best age 1σ
275
296
325
271
230
274
331
319
288
335
314
305
327
302
308
330
298
305
207 Pb/206 U
Ages (Ma)
87
0.02
0.36
0.18
0.43
0.48
Zrc_84_107
Zrc_39_053
Zrc_21_032
Zrc_08_016
0.38
Zrc_57_075
0.38
0.55
Zrc_06_014
Zrc_13_022
Th/U
Spot name
Zrc_81_104
0.36
0.58
Zrc_73_094
0.44
Zrc_60_078
Zrc_45_060
0.38
Zrc_63_082
Spot name Th/U
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
2.80 0.36256 2.87 0.04923 0.65 0.23
1.91 0.34846 1.98 0.04870 0.55 0.27
1.70 0.34822 1.79 0.04822 0.56 0.31
2.20 0.37221 2.37 0.04794 0.90 0.37
1σ
310
307
304
302
206 Pb/238 U
2
2
2
3
1σ
314
304
303
321
207 Pb/235 U
8
5
5
7
1σ
355
281
303
463
207 Pb/206 U
Ages (Ma)
0.07491
0.07474
0.07408
0.07287
0.07208
0.07165
0.07098
0.06802
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
1.29 1.76560 1.38 0.17138 0.46 0.34
0.83 1.87920 0.91 0.18265 0.37 0.41
0.86 1.74320 0.94 0.17084 0.37 0.39
0.84 1.67810 0.91 0.16724 0.36 0.40
1.53 1.66974 1.73 0.16802 0.45 0.37
0.75 1.61810 0.84 0.16398 0.36 0.44
0.85 1.52490 0.92 0.15600 0.34 0.38
1.71 1.06950 1.94 0.11398 0.93 0.47
1σ
1020
1081
1017
997
1001
979
935
696
206 Pb/238 U
4
4
3
3
4
3
3
6
1σ
1033
1074
1025
1000
997
977
940
738
207 Pb/235 U
9
6
6
6
11
5
6
10
1σ
310
307
304
302
2
2
2
3
26
15
16
17
31
14
17
35
1066
1062
1044
1010
1001
979
935
696
26
15
16
17
4
3
3
6
1σ Best age 1σ
59
43
36
46
1σ Best age 1σ
1066
1062
1044
1010
988
976
957
869
207 Pb/206 U
Ages (Ma)
Tabla 4: LA-ICP-MS U-Pb isotopic data for Tecomate Formation metapsammite TT-486A.
0.05361
0.05190
0.05240
0.05626
207 Pb/206 Pb
88
0.51
0.44
0.31
0.34
0.78
Zrc_99_125
Zrc_07_015
Zrc_63_082
0.28
Zrc_47_063
Zrc_55_072
0.06
Zrc_83_106
Zrc_70_090
0.53
0.47
Zrc_19_029
0.48
Zrc_05_012
Zrc_78_100
0.81
0.22
0.22
Zrc_15_024
Zrc_16_026
0.39
Zrc_25_036
Zrc_72_093
0.26
0.32
0.12
Zrc_67_087
Zrc_97_123
0.38
Zrc_93_118
Zrc_54_071
Th/U
Spot name
0.07801
0.07793
0.07790
0.07790
0.07783
0.07784
0.07781
0.07773
0.07766
0.07748
0.07745
0.07730
0.07730
0.07708
0.07686
0.07651
0.07606
0.07492
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
0.79 2.16540 0.87 0.20144 0.35 0.41
0.89 2.13660 1.01 0.19894 0.47 0.48
0.95 2.13890 1.03 0.19927 0.41 0.40
1.00 2.14200 1.07 0.19967 0.38 0.35
1.90 1.88790 1.97 0.17650 0.52 0.26
0.87 2.08620 0.95 0.19451 0.35 0.39
0.87 2.09840 0.93 0.19576 0.34 0.35
0.81 2.02400 0.89 0.18904 0.36 0.40
1.70 2.07240 1.84 0.19409 0.71 0.39
0.83 2.04260 0.90 0.19138 0.34 0.39
0.98 1.97950 1.10 0.18577 0.49 0.44
1.20 1.93710 1.28 0.18209 0.45 0.35
1.20 1.93710 1.28 0.18209 0.45 0.35
1.60 1.74460 1.70 0.16436 0.57 0.34
1.70 1.92070 1.76 0.18136 0.45 0.25
1.01 1.70040 1.89 0.16053 1.60 0.85
1.00 2.25670 1.08 0.21545 0.41 0.38
1.09 1.79300 1.15 0.17388 0.35 0.32
1σ
1183
1170
1171
1174
1048
1146
1153
1116
1143
1129
1098
1078
1078
981
1074
960
1258
1033
206 Pb/238 U
4
5
4
4
5
4
4
4
7
4
5
4
4
5
4
14
5
3
1σ
1170
1161
1161
1162
1077
1144
1148
1124
1140
1130
1109
1094
1094
1025
1088
1009
1199
1043
207 Pb/235 U
6
7
7
7
13
7
6
6
13
6
7
9
9
11
12
12
8
8
1σ
16
17
19
20
35
16
17
16
31
15
19
22
22
29
31
20
20
22
1147
1145
1144
1144
1143
1143
1142
1140
1138
1134
1133
1129
1129
1123
1118
1108
1097
1066
16
17
19
20
35
16
17
16
31
15
19
22
22
29
31
20
20
22
1σ Best age 1σ
1147
1145
1144
1144
1143
1143
1142
1140
1138
1134
1133
1129
1129
1123
1118
1108
1097
1066
207 Pb/206 U
Ages (Ma)
89
0.31
0.71
0.32
0.18
0.22
Zrc_51_068
Zrc_66_086
Zrc_27_039
0.27
Zrc_82_105
Zrc_80_102
0.38
Zrc_64_083
Zrc_74_095
0.14
0.33
Zrc_04_011
0.23
Zrc_65_084
Zrc_46_062
0.36
0.71
0.51
Zrc_96_122
Zrc_45_060
0.48
Zrc_76_098
Zrc_31_044
0.48
0.44
0.64
Zrc_53_070
Zrc_58_076
0.26
Zrc_94_119
Zrc_98_124
Th/U
Spot name
0.07905
0.07893
0.07893
0.07889
0.07877
0.07865
0.07863
0.07864
0.07862
0.07859
0.07861
0.07854
0.07843
0.07837
0.07829
0.07828
0.07813
0.07806
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
0.83 2.18130 0.93 0.20051 0.39 0.43
1.20 2.36360 1.34 0.21732 0.60 0.44
0.95 2.14820 1.04 0.19759 0.43 0.41
0.93 2.11920 1.00 0.19500 0.38 0.39
1.21 2.14520 1.29 0.19785 0.48 0.36
1.28 2.17279 1.47 0.20037 0.46 0.40
0.86 2.15870 0.92 0.19931 0.34 0.35
1.00 2.11060 1.07 0.19493 0.39 0.35
0.83 2.22390 0.90 0.20541 0.35 0.40
0.89 2.13310 0.96 0.19702 0.35 0.36
1.00 2.15620 1.21 0.19921 0.68 0.56
0.78 2.17930 0.85 0.20134 0.33 0.40
0.92 2.13540 1.00 0.19760 0.39 0.40
1.30 1.98910 1.41 0.18436 0.55 0.39
0.88 2.23180 1.08 0.20711 0.63 0.58
1.00 2.12090 1.08 0.19669 0.40 0.38
1.42 2.08883 1.74 0.19390 0.51 0.49
0.99 2.09030 1.08 0.19444 0.42 0.40
1σ
1178
1268
1162
1148
1164
1177
1172
1148
1204
1159
1171
1183
1162
1091
1213
1158
1142
1145
206 Pb/238 U
4
7
5
4
5
5
4
4
4
4
7
4
4
5
7
4
5
4
1σ
1175
1232
1164
1155
1164
1172
1168
1152
1189
1160
1167
1174
1160
1112
1191
1156
1145
1146
207 Pb/235 U
6
10
7
7
9
10
6
7
6
7
8
6
7
10
8
7
12
7
1σ
15
23
17
18
23
25
17
18
15
17
18
14
18
25
17
19
26
19
1173
1170
1170
1169
1166
1163
1163
1163
1163
1162
1162
1161
1158
1156
1154
1154
1150
1148
15
23
17
18
23
25
17
18
15
17
18
14
18
25
17
19
26
19
1σ Best age 1σ
1173
1170
1170
1169
1166
1163
1163
1163
1163
1162
1162
1161
1158
1156
1154
1154
1150
1148
207 Pb/206 U
Ages (Ma)
90
0.35
0.59
0.36
0.29
0.08
Zrc_23_034
Zrc_60_078
Zrc_44_059
0.28
Zrc_43_058
Zrc_59_077
0.37
Zrc_75_096
Zrc_88_112
0.33
0.51
Zrc_50_066
0.40
Zrc_22_033
Zrc_35_048
0.32
0.48
0.58
Zrc_86_110
Zrc_12_021
0.72
Zrc_52_069
Zrc_09_017
0.69
0.51
0.40
Zrc_24_035
Zrc_29_041
0.39
Zrc_14_023
Zrc_36_050
Th/U
Spot name
0.08259
0.08234
0.08198
0.08119
0.08108
0.08076
0.08071
0.08059
0.08049
0.08044
0.08024
0.08009
0.07990
0.07966
0.07955
0.07955
0.07957
0.07908
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
1.30 2.45410 1.46 0.21583 0.67 0.46
1.51 2.28400 1.57 0.20167 0.48 0.29
1.00 2.28860 1.11 0.20279 0.49 0.44
1.31 2.34130 1.42 0.20914 0.57 0.39
1.10 2.33210 1.18 0.20885 0.43 0.37
0.99 2.33120 1.06 0.20962 0.39 0.37
1.40 2.16760 1.50 0.19519 0.53 0.35
1.91 2.31160 2.19 0.20803 0.50 0.34
0.99 2.19340 1.08 0.19800 0.42 0.40
0.92 2.25650 1.00 0.20388 0.40 0.40
1.50 2.17780 1.56 0.19709 0.41 0.27
1.10 2.26130 1.20 0.20505 0.48 0.40
1.20 2.15900 1.28 0.19617 0.44 0.34
1.00 2.22120 1.07 0.20227 0.37 0.34
1.29 2.20740 1.38 0.20154 0.45 0.34
1.11 2.12060 1.15 0.19366 0.34 0.28
1.28 2.17300 1.49 0.19806 0.42 0.35
1.40 2.22390 1.49 0.20451 0.50 0.33
1σ
1260
1184
1190
1224
1223
1227
1149
1218
1165
1196
1160
1202
1155
1188
1184
1141
1165
1200
206 Pb/238 U
8
5
5
6
5
4
6
6
4
4
4
5
5
4
5
4
5
5
1σ
1259
1207
1209
1225
1222
1222
1171
1216
1179
1199
1174
1200
1168
1188
1183
1156
1172
1189
207 Pb/235 U
11
11
8
10
8
8
10
16
8
7
11
8
9
7
10
8
10
10
1σ
23
29
18
25
21
18
27
35
18
17
29
20
23
18
23
20
23
25
1260
1254
1245
1226
1223
1216
1214
1212
1209
1208
1203
1199
1195
1189
1186
1186
1186
1174
23
29
18
25
21
18
27
35
18
17
29
20
23
18
23
20
23
25
1σ Best age 1σ
1260
1254
1245
1226
1223
1216
1214
1212
1209
1208
1203
1199
1195
1189
1186
1186
1186
1174
207 Pb/206 U
Ages (Ma)
91
0.64
0.20
0.25
0.27
0.50
Zrc_71_092
Zrc_01_008
Zrc_87_111
0.35
Zrc_69_089
Zrc_11_020
1.53
Zrc_48_064
Zrc_37_051
0.53
0.43
Zrc_77_099
0.25
Zrc_10_018
Zrc_26_038
0.03
0.44
0.02
Zrc_38_052
Zrc_56_074
0.54
Zrc_18_028
Zrc_03_010
0.33
0.53
0.36
Zrc_33_046
Zrc_28_040
0.28
Zrc_85_108
Zrc_61_080
Th/U
Spot name
0.08565
0.08543
0.08517
0.08511
0.08511
0.08494
0.08459
0.08460
0.08432
0.08361
0.08349
0.08330
0.08323
0.08318
0.08297
0.08300
0.08296
0.08262
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
1.00 2.87220 1.09 0.24341 0.43 0.39
1.53 2.66924 1.66 0.22660 0.45 0.34
0.79 2.68620 0.85 0.22880 0.32 0.39
0.80 2.71160 0.87 0.23117 0.35 0.40
1.10 2.69740 1.20 0.23005 0.48 0.39
0.77 2.59930 0.83 0.22209 0.34 0.39
0.93 2.57470 1.01 0.22100 0.39 0.38
1.50 2.50280 1.56 0.21507 0.44 0.28
1.00 2.60860 1.08 0.22464 0.42 0.40
0.80 1.96430 1.07 0.17031 0.71 0.66
1.40 2.31180 1.54 0.20139 0.63 0.41
1.20 2.25620 1.27 0.19693 0.43 0.34
0.83 2.49260 1.02 0.21737 0.59 0.58
1.00 2.34660 1.09 0.20493 0.43 0.40
1.21 2.29140 1.29 0.20038 0.48 0.36
0.89 2.38370 1.00 0.20866 0.45 0.45
1.10 2.30810 1.17 0.20211 0.41 0.36
0.92 2.34640 0.99 0.20602 0.36 0.36
1σ
1404
1317
1328
1341
1335
1293
1287
1256
1306
1014
1183
1159
1268
1202
1177
1222
1187
1208
206 Pb/238 U
5
5
4
4
6
4
5
5
5
7
7
5
7
5
5
5
4
4
1σ
1375
1320
1325
1332
1328
1300
1293
1273
1303
1103
1216
1199
1270
1227
1210
1238
1215
1226
207 Pb/235 U
8
12
6
6
9
6
7
11
8
7
11
9
7
8
9
7
8
7
1σ
19
27
15
14
19
15
17
27
19
14
25
21
15
18
23
16
20
18
1330
1325
1319
1318
1318
1314
1306
1306
1300
1283
1281
1276
1275
1273
1269
1269
1268
1260
19
27
15
14
19
15
17
27
19
14
25
21
15
18
23
16
20
18
1σ Best age 1σ
1330
1325
1319
1318
1318
1314
1306
1306
1300
1283
1281
1276
1275
1273
1269
1269
1268
1260
207 Pb/206 U
Ages (Ma)
92
0.21
0.46
0.38
0.62
0.32
Zrc_89_113
Zrc_17_027
Zrc_90_114
0.53
Zrc_92_117
Zrc_49_065
0.22
Zrc_100_126
Zrc_79_101
0.37
0.34
Zrc_73_094
0.17
Zrc_91_116
Zrc_34_047
0.29
0.19
0.20
Zrc_40_054
Zrc_62_081
0.27
Zrc_41_056
Zrc_20_030
0.40
0.40
0.27
Zrc_95_120
Zrc_42_057
0.26
Zrc_02_009
Zrc_30_042
Th/U
Spot name
0.09948
0.09892
0.09864
0.09840
0.09835
0.09672
0.09544
0.09527
0.09363
0.09303
0.09269
0.09249
0.09185
0.09089
0.09067
0.09045
0.08983
0.08751
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
1.00 3.91220 1.09 0.28572 0.44 0.41
0.97 3.93380 1.16 0.28860 0.63 0.54
0.81 3.81130 0.88 0.28037 0.35 0.39
0.80 3.67780 0.88 0.27133 0.37 0.41
0.99 3.75920 1.06 0.27768 0.39 0.38
0.78 3.55400 0.85 0.26675 0.33 0.40
1.05 3.57218 1.17 0.27146 0.41 0.45
0.89 3.36210 1.07 0.25626 0.59 0.55
0.85 3.22380 0.96 0.24982 0.45 0.46
0.89 3.43710 0.98 0.26825 0.42 0.42
0.83 3.36360 0.92 0.26348 0.39 0.42
0.99 3.37910 1.05 0.26525 0.36 0.33
0.87 2.94167 1.07 0.23227 0.45 0.48
0.83 3.20960 0.93 0.25643 0.42 0.46
0.92 3.12970 0.99 0.25053 0.37 0.38
0.78 2.65160 0.89 0.21279 0.40 0.46
0.83 2.92800 0.95 0.23655 0.46 0.48
1.10 2.83160 1.20 0.23509 0.48 0.41
1σ
1620
1635
1593
1548
1580
1524
1548
1471
1438
1532
1508
1517
1346
1472
1441
1244
1369
1361
206 Pb/238 U
6
9
5
5
5
4
6
8
6
6
5
5
5
6
5
5
6
6
1σ
1616
1621
1595
1567
1584
1539
1543
1496
1463
1513
1496
1500
1393
1459
1440
1315
1389
1364
207 Pb/235 U
9
9
7
7
9
7
9
8
7
8
7
8
8
7
8
7
7
9
1σ
18
17
15
15
17
14
18
15
16
17
14
19
15
14
16
14
16
19
1614
1604
1599
1594
1593
1562
1537
1533
1501
1488
1482
1477
1464
1444
1440
1435
1422
1372
18
17
15
15
17
14
18
15
16
17
14
19
15
14
16
14
16
19
1σ Best age 1σ
1614
1604
1599
1594
1593
1562
1537
1533
1501
1488
1482
1477
1464
1444
1440
1435
1422
1372
207 Pb/206 U
Ages (Ma)
93
0.44
0.49
0.63
0.56
0.46
0.79
Zrc_34_047
Zrc_03_010
Zrc_51_068
Zrc_36_050
0.72
Zrc_23_034
Zrc_65_084
0.34
Zrc_67_087
Zrc_05_012
0.44
0.52
Zrc_90_114
1.73
Zrc_44_059
Zrc_06_014
Th/U
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
0.75 4.99470 0.93 0.32676 0.55 0.59
1σ
1823
206 Pb/238 U
9
1σ
1818
207 Pb/235 U
8
1σ
1816
207 Pb/206 U
Ages (Ma)
0.05694
0.05492
0.05714
0.04862
0.05360
0.05280
0.05280
0.05410
0.05363
0.05725
0.08570
0.32902
0.34157
0.40647
207 Pb/235 U
2.37
6.14
2.37
1σ
1σ Rho
0.04451 0.58 0.25
0.04327 1.73 0.32
0.03512 0.88 0.37
206 Pb/238 U
0.33552
0.32904
0.32862
2.39
2.39
1.70
0.04530 0.66 0.28
0.04518 0.64 0.28
0.04503 0.58 0.35
2.79
6.99
1.51
0.36390
0.34671
0.36112
2.95
7.35
1.58
0.04640 0.93 0.32
0.04578 0.81 0.21
0.04573 0.50 0.31
10.02 0.30453 10.44 0.04543 0.90 0.10
2.29
2.29
1.59
13.11 0.33403 14.03 0.04478 1.43 0.25
2.29
5.40
2.21
1σ
292
289
288
286
286
285
284
282
281
273
223
206 Pb/238 U
3
2
1
3
2
2
2
4
2
5
2
1σ
315
302
313
270
294
289
289
293
289
298
346
207 Pb/235 U
8
19
4
25
6
6
4
36
6
16
7
1σ
1816
12
61
154
33
210
51
51
36
285
51
118
41
292
289
288
286
286
285
284
282
281
273
223
3
2
1
3
2
2
2
4
2
5
2
1σ Best age 1σ
12
1σ Best age 1σ
489
409
497
129
354
320
320
375
356
501
1331
207 Pb/206 U
Ages (Ma)
Tabla 5: LA-ICP-MS U-Pb isotopic data for Tecomate Formation metapsammite TT-81.
0.11098
207 Pb/206 Pb
207 Pb/206 Pb
0.55
Zrc_32_045
Spot name
Th/U
Spot name
94
0.30
0.52
0.75
0.47
0.56
Zrc_63_082
Zrc_92_117
Zrc_14_023
0.28
Zrc_85_108
Zrc_95_120
0.59
Zrc_02_009
Zrc_40_054
0.60
0.35
Zrc_04_011
0.60
Zrc_11_020
Zrc_12_021
0.13
0.34
0.11
Zrc_88_112
Zrc_58_076
0.33
Zrc_38_052
Zrc_72_093
0.34
0.50
0.44
Zrc_54_071
Zrc_83_106
0.51
Zrc_52_069
Zrc_09_017
Th/U
Spot name
0.05349
0.05774
0.05395
0.05245
0.05284
0.05994
0.05286
0.05270
0.05307
0.05230
0.05247
0.05330
0.05414
0.05332
0.05139
0.05639
0.05580
0.05631
207 Pb/206 Pb
1.79
1.70
2.30
1.91
1.61
1.80
1.61
2.50
1.51
1.40
1.94
1.80
2.20
2.01
2.80
2.50
2.01
1.90
1σ
0.36143
0.38779
0.36384
0.35339
0.35533
0.40240
0.35513
0.35146
0.35465
0.34653
0.34326
0.34921
0.35308
0.34742
0.33197
0.36381
0.35721
0.36371
207 Pb/235 U
1.90
1.79
2.40
2.01
1.70
1.88
1.69
2.57
1.56
1.48
2.33
1.87
2.29
2.20
2.91
2.58
2.09
2.13
1σ
1σ Rho
0.04891 0.59 0.32
0.04870 0.55 0.31
0.04871 0.68 0.28
0.04874 0.66 0.32
0.04866 0.58 0.32
0.04856 0.54 0.28
0.04860 0.53 0.30
0.04831 0.62 0.23
0.04836 0.43 0.26
0.04802 0.48 0.33
0.04744 0.72 0.50
0.04740 0.51 0.27
0.04725 0.66 0.29
0.04710 0.91 0.41
0.04698 0.79 0.27
0.04681 0.62 0.24
0.04635 0.60 0.28
0.04638 0.97 0.45
206 Pb/238 U
308
307
307
307
306
306
306
304
304
302
299
299
298
297
296
295
292
292
206 Pb/238 U
2
2
2
2
2
2
2
2
1
1
2
1
2
3
2
2
2
3
1σ
313
333
315
307
309
343
309
306
308
302
300
304
307
303
291
315
310
315
207 Pb/235 U
5
5
6
5
5
5
4
7
4
4
6
5
6
6
7
7
6
6
1σ
40
37
50
42
36
38
38
56
34
31
43
39
49
45
64
55
43
41
308
307
307
307
306
306
306
304
304
302
299
299
298
297
296
295
292
292
2
2
2
2
2
2
2
2
1
1
2
1
2
3
2
2
2
3
1σ Best age 1σ
350
520
369
305
322
601
323
316
332
299
306
342
377
342
258
468
444
465
207 Pb/206 U
Ages (Ma)
95
0.44
0.27
0.52
0.43
0.35
Zrc_21_032
Zrc_56_074
Zrc_59_077
0.78
Zrc_71_092
Zrc_01_008
0.39
Zrc_81_104
Zrc_82_105
0.61
0.52
Zrc_26_038
0.50
Zrc_18_028
Zrc_53_070
0.39
0.51
0.55
Zrc_50_066
Zrc_15_024
0.48
Zrc_29_041
Zrc_35_048
0.53
0.36
0.58
Zrc_75_096
Zrc_87_111
0.37
Zrc_27_039
Zrc_20_030
Th/U
Spot name
0.05387
0.05568
0.05233
0.05347
0.05232
0.05197
0.05286
0.05213
0.05401
0.05120
0.05191
0.05273
0.05441
0.05346
0.05199
0.05608
0.05456
0.05148
207 Pb/206 Pb
2.41
1.90
1.80
2.00
1.80
1.50
1.89
1.59
2.50
1.60
1.60
2.60
2.79
2.10
1.50
1.60
3.74
2.10
1σ
0.37536
0.38848
0.36150
0.37195
0.36258
0.35929
0.36516
0.35858
0.36869
0.35085
0.35381
0.35794
0.36785
0.36249
0.35253
0.37935
0.36866
0.34803
207 Pb/235 U
2.78
1.97
3.00
2.09
1.93
1.59
1.99
1.70
2.60
1.70
1.70
2.69
2.89
2.18
1.57
1.72
4.20
2.21
1σ
1σ Rho
0.05054 0.77 0.35
0.05054 0.51 0.26
0.05054 2.39 0.80
0.05036 0.62 0.30
0.05021 0.70 0.36
0.05003 0.54 0.34
0.04990 0.60 0.32
0.04983 0.58 0.35
0.04957 0.73 0.28
0.04960 0.58 0.34
0.04941 0.59 0.34
0.04921 0.67 0.26
0.04905 0.69 0.25
0.04908 0.57 0.28
0.04909 0.47 0.29
0.04894 0.63 0.37
0.04901 0.90 0.29
0.04897 0.69 0.32
206 Pb/238 U
318
318
318
317
316
315
314
313
312
312
311
310
309
309
309
308
308
308
206 Pb/238 U
2
2
7
2
2
2
2
2
2
2
2
2
2
2
1
2
3
2
1σ
324
333
313
321
314
312
316
311
319
305
308
311
318
314
307
327
319
303
207 Pb/235 U
8
6
8
6
5
4
5
5
7
4
5
7
8
6
4
5
12
6
1σ
53
41
40
45
43
34
42
35
56
36
36
59
61
47
34
35
83
48
318
318
318
317
316
315
314
313
312
312
311
310
309
309
309
308
308
308
2
2
7
2
2
2
2
2
2
2
2
2
2
2
1
2
3
2
1σ Best age 1σ
366
440
300
349
299
284
323
291
371
250
281
317
388
348
285
456
394
262
207 Pb/206 U
Ages (Ma)
96
0.26
0.31
0.24
0.27
0.19
Zrc_69_089
Zrc_68_088
Zrc_43_058
0.43
Zrc_89_113
Zrc_45_060
0.33
Zrc_19_029
Zrc_66_086
0.19
1.21
Zrc_74_095
0.44
Zrc_94_119
Zrc_32_045
0.39
0.33
0.72
Zrc_41_056
Zrc_42_057
0.69
Zrc_33_046
Zrc_61_080
0.55
0.33
0.45
Zrc_93_118
Zrc_07_015
0.28
Zrc_70_090
Zrc_91_116
Th/U
Spot name
0.05897
0.06736
0.06360
0.06834
0.05689
0.07007
0.06291
0.05564
0.05788
0.06011
0.05708
0.06044
0.05370
0.05594
0.05403
0.05520
0.05289
0.05384
207 Pb/206 Pb
1.49
2.81
1.79
2.40
1.30
1.80
1.61
1.20
1.83
5.19
2.59
6.63
1.81
2.09
1.70
2.57
1.80
2.15
1σ
0.68338
0.78278
0.73058
0.80177
0.60981
0.77362
0.63835
0.56124
0.51317
0.47211
0.41128
0.43571
0.38559
0.39991
0.38347
0.39132
0.36983
0.37519
207 Pb/235 U
1.57
3.18
2.11
4.00
1.41
3.24
2.41
1.31
2.00
7.14
2.73
6.92
2.00
2.31
1.78
2.92
1.90
2.39
1σ
1σ Rho
0.08391 0.46 0.31
0.08362 1.49 0.47
0.08111 1.10 0.53
0.08010 3.20 0.80
0.07757 0.54 0.38
0.07738 2.70 0.83
0.07330 1.80 0.75
0.07302 0.52 0.39
0.06430 0.58 0.31
0.05697 2.76 0.68
0.05228 0.84 0.32
0.05228 0.71 0.13
0.05198 0.88 0.43
0.05176 0.95 0.42
0.05142 0.53 0.29
0.05141 0.76 0.38
0.05064 0.59 0.32
0.05054 0.65 0.31
206 Pb/238 U
519
518
503
497
482
480
456
454
402
357
329
329
327
325
323
323
318
318
206 Pb/238 U
2
7
5
15
3
13
8
2
2
10
3
2
3
3
2
2
2
2
1σ
529
587
557
598
483
582
501
452
421
393
350
367
331
342
330
335
320
323
207 Pb/235 U
6
14
9
18
5
14
10
5
7
23
8
21
6
7
5
8
5
7
1σ
31
57
37
48
28
36
34
26
39
112
55
141
39
46
38
57
40
48
519
518
503
497
482
480
456
454
402
357
329
329
327
325
323
323
318
318
2
7
5
15
3
13
8
2
2
10
3
2
3
3
2
2
2
2
1σ Best age 1σ
566
849
728
879
487
930
705
438
525
607
495
620
358
450
372
420
324
364
207 Pb/206 U
Ages (Ma)
97
0.32
0.23
0.37
0.10
0.60
Zrc_96_122
Zrc_100_126
Zrc_57_075
0.26
Zrc_39_053
Zrc_49_065
0.35
Zrc_13_022
Zrc_30_042
0.42
0.39
Zrc_55_072
0.35
Zrc_86_110
Zrc_17_027
0.05
0.39
0.22
Zrc_73_094
Zrc_10_018
0.28
Zrc_80_102
Zrc_31_044
0.18
0.57
0.25
Zrc_76_098
Zrc_60_078
0.88
Zrc_16_026
Zrc_47_063
Th/U
Spot name
0.08236
0.08148
0.07810
0.07651
0.07508
0.07416
0.07365
0.07314
0.07151
0.06949
0.06890
0.07258
0.06787
0.07045
0.06674
0.06770
0.06204
0.05909
207 Pb/206 Pb
2.00
0.99
1.20
1.01
1.20
1.29
1.40
1.09
1.96
1.42
1.20
0.99
1.11
1.41
2.08
1.30
2.00
1.69
1σ
2.33510
1.89550
1.94180
1.91090
1.84750
1.75821
1.76040
1.78850
1.60304
1.49016
1.33810
1.35909
1.25740
1.28180
1.18944
1.06170
0.84777
0.75452
207 Pb/235 U
2.15
1.11
1.48
1.08
1.35
1.60
1.52
1.19
2.26
1.69
1.31
1.11
1.70
1.70
2.46
1.59
2.90
1.79
1σ
1σ Rho
0.20546 0.80 0.37
0.16787 0.48 0.44
0.17928 0.87 0.58
0.18069 0.41 0.36
0.17778 0.61 0.46
0.17196 0.62 0.51
0.17311 0.59 0.39
0.17707 0.45 0.39
0.16259 0.62 0.37
0.15554 0.55 0.43
0.14055 0.52 0.39
0.13582 0.52 0.43
0.13323 1.30 0.76
0.13085 0.96 0.56
0.12925 0.67 0.41
0.11301 0.92 0.58
0.09377 2.10 0.72
0.09249 0.55 0.32
206 Pb/238 U
1205
1000
1063
1071
1055
1023
1029
1051
971
932
848
821
806
793
784
690
578
570
206 Pb/238 U
9
4
9
4
6
6
6
4
6
5
4
4
10
7
5
6
12
3
1σ
1223
1080
1096
1085
1063
1030
1031
1041
971
926
862
871
827
838
796
735
623
571
207 Pb/235 U
15
7
10
7
9
10
10
8
14
10
8
6
10
10
14
8
14
8
1σ
38
19
23
20
23
25
28
22
39
29
24
20
22
28
42
26
42
36
1254
1233
1149
1108
1071
1046
1032
1018
971
932
848
821
806
793
784
690
578
570
38
19
23
20
23
25
28
22
6
5
4
4
10
7
5
6
12
3
1σ Best age 1σ
1254
1233
1149
1108
1071
1046
1032
1018
972
913
896
1002
865
942
830
859
676
570
207 Pb/206 U
Ages (Ma)
98
0.45
0.64
1.09
0.71
0.79
0.37
Zrc_33_048
Zrc_97_125
Zrc_37_053
Zrc_93_120
0.89
Zrc_14_023
Zrc_09_017
0.83
Zrc_53_072
Zrc_99_127
0.07
0.92
Zrc_46_062
Zrc_19_029
0.37
Zrc_37_051
Th/U
0.30
Zrc_25_036
0.96
1.00
1.10
1σ
4.84970
2.91770
2.41160
207 Pb/235 U
1.09
1.10
1.18
1σ
1σ Rho
0.31958 0.51 0.48
0.23625 0.45 0.42
0.21017 0.44 0.38
206 Pb/238 U
1788
1367
1230
206 Pb/238 U
8
6
5
1σ
1794
1387
1246
207 Pb/235 U
9
8
9
1σ
0.05420
0.05285
0.05288
0.05314
0.05570
0.05175
0.05308
0.05351
0.05117
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
2.90 0.35777 3.00 0.04786 0.75 0.26
2.50 0.34677 2.59 0.04770 0.67 0.26
1.70 0.34672 1.78 0.04752 0.53 0.29
1.39 0.34730 1.45 0.04739 0.38 0.29
3.59 0.36200 3.85 0.04713 0.62 0.29
1.70 0.33431 1.94 0.04692 0.94 0.48
1.81 0.33862 1.88 0.04628 0.56 0.28
2.69 0.33301 2.80 0.04517 0.75 0.28
1.50 0.31544 1.56 0.04470 0.43 0.26
1σ
301
300
299
298
297
296
292
285
282
206 Pb/238 U
2
2
2
1
2
3
2
2
1
1σ
311
302
302
303
314
293
296
292
278
207 Pb/235 U
8
7
5
4
10
5
5
7
4
1σ
1796
1411
1269
17
19
21
63
56
37
31
77
38
40
60
34
301
300
299
298
297
296
292
285
282
2
2
2
1
2
3
2
2
1
1σ Best age 1σ
17
19
21
1σ Best age 1σ
379
322
324
335
441
274
332
350
248
207 Pb/206 U
Ages (Ma)
1796
1411
1269
207 Pb/206 U
Ages (Ma)
Tabla 6: LA-ICP-MS U-Pb isotopic data for Tecomate Formation metapelite TT-82.
0.10979
0.08933
0.08299
207 Pb/206 Pb
Spot name
Th/U
Spot name
99
0.71
0.42
0.87
0.44
0.93
Zrc_70_092
Zrc_80_104
Zrc_98_126
0.49
Zrc_92_119
Zrc_16_026
0.57
Zrc_52_071
Zrc_78_102
0.91
0.62
Zrc_65_086
0.83
Zrc_87_113
Zrc_23_036
0.62
0.60
0.68
Zrc_79_103
Zrc_25_038
0.39
Zrc_68_090
Zrc_73_096
0.44
0.58
0.47
Zrc_40_056
Zrc_13_022
0.77
Zrc_77_101
Zrc_69_091
Th/U
Spot name
0.05158
0.07303
0.05808
0.05371
0.05577
0.05447
0.05614
0.05701
0.05456
0.05283
0.05306
0.05521
0.05298
0.05279
0.05223
0.05281
0.05143
0.05444
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
2.00 0.38061 2.07 0.05354 0.52 0.26
2.62 0.53704 2.96 0.05333 0.83 0.41
2.70 0.42251 3.03 0.05276 0.59 0.24
1.99 0.38895 2.07 0.05249 0.53 0.28
4.27 0.40419 4.67 0.05256 0.80 0.24
1.60 0.37827 1.65 0.05037 0.42 0.26
1.91 0.38937 1.96 0.05036 0.48 0.23
4.14 0.39524 4.41 0.05028 0.56 0.26
1.70 0.37160 1.78 0.04934 0.51 0.28
1.50 0.35782 1.56 0.04907 0.43 0.28
2.60 0.35836 2.70 0.04912 0.71 0.26
3.10 0.36981 3.19 0.04876 0.76 0.24
1.70 0.35575 1.76 0.04868 0.45 0.26
2.60 0.35256 2.71 0.04853 0.76 0.29
1.90 0.34731 1.98 0.04821 0.56 0.29
2.40 0.35093 2.47 0.04826 0.58 0.23
2.51 0.34072 2.58 0.04805 0.62 0.23
1.51 0.36050 1.56 0.04798 0.42 0.25
1σ
336
335
331
330
330
317
317
316
310
309
309
307
306
305
304
304
303
302
206 Pb/238 U
2
3
2
2
3
1
1
2
2
1
2
2
1
2
2
2
2
1
1σ
327
436
358
334
345
326
334
338
321
311
311
320
309
307
303
305
298
313
207 Pb/235 U
6
10
9
6
14
5
6
13
5
4
7
9
5
7
5
7
7
4
1σ
44
53
58
45
92
35
42
89
37
34
59
67
39
57
42
53
57
34
336
335
331
330
330
317
317
316
310
309
309
307
306
305
304
304
303
302
2
3
2
2
3
1
1
2
2
1
2
2
1
2
2
2
2
1
1σ Best age 1σ
267
1015
533
359
443
391
458
492
394
322
331
421
328
320
295
321
260
389
207 Pb/206 U
Ages (Ma)
100
0.37
0.36
0.41
1.01
0.38
Zrc_36_052
Zrc_18_028
Zrc_34_049
0.41
Zrc_21_034
Zrc_10_018
0.68
Zrc_22_035
Zrc_08_016
0.24
0.31
Zrc_42_059
0.83
Zrc_45_062
Zrc_06_014
0.24
0.35
0.62
Zrc_63_084
Zrc_88_114
0.76
Zrc_27_041
Zrc_57_077
0.08
0.49
0.75
Zrc_75_098
Zrc_47_065
0.60
Zrc_67_089
Zrc_64_085
Th/U
Spot name
0.05990
0.05962
0.06499
0.07085
0.05841
0.05878
0.05801
0.05873
0.05636
0.05603
0.05898
0.05487
0.05649
0.05456
0.05512
0.05253
0.05434
0.05589
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
1.90 0.76137 1.95 0.09233 0.43 0.21
1.39 0.74145 1.53 0.08994 0.63 0.42
1.49 0.80320 1.86 0.08811 1.10 0.60
2.10 0.84627 2.39 0.08663 0.70 0.34
1.51 0.69767 1.68 0.08639 0.75 0.44
1.80 0.69653 1.85 0.08597 0.43 0.22
1.40 0.68403 1.47 0.08547 0.44 0.31
1.80 0.64366 1.87 0.07953 0.49 0.25
1.40 0.59644 1.46 0.07670 0.40 0.27
1.61 0.58522 1.67 0.07572 0.48 0.27
2.10 0.58513 3.04 0.06904 2.20 0.72
1.29 0.46724 1.40 0.06160 0.50 0.37
2.80 0.45353 2.88 0.05778 0.67 0.24
2.11 0.42411 2.37 0.05605 1.11 0.46
2.00 0.41858 2.23 0.05485 0.98 0.44
1.41 0.39526 1.45 0.05455 0.38 0.24
2.10 0.40561 2.16 0.05408 0.52 0.24
1.81 0.41577 1.87 0.05369 0.50 0.26
1σ
569
555
544
536
534
532
529
493
476
471
430
385
362
352
344
342
340
337
206 Pb/238 U
2
3
6
4
4
2
2
2
2
2
9
2
2
4
3
1
2
2
1σ
575
563
599
623
537
537
529
505
475
468
468
389
380
359
355
338
346
353
207 Pb/235 U
9
7
8
11
7
8
6
7
6
6
11
5
9
7
7
4
6
6
1σ
41
29
31
42
32
38
30
38
31
35
45
29
60
46
43
32
47
39
569
555
544
536
534
532
529
493
476
471
430
385
362
352
344
342
340
337
2
3
6
4
4
2
2
2
2
2
9
2
2
4
3
1
2
2
1σ Best age 1σ
600
590
774
953
545
559
530
557
467
454
566
407
472
394
417
309
385
448
207 Pb/206 U
Ages (Ma)
101
0.57
0.34
0.30
0.24
0.35
Zrc_44_061
Zrc_35_050
Zrc_59_079
0.24
Zrc_72_095
Zrc_30_044
0.41
Zrc_55_074
Zrc_39_055
0.45
0.23
Zrc_94_121
0.27
Zrc_02_009
Zrc_71_094
0.06
0.31
0.33
Zrc_31_046
Zrc_83_108
0.40
Zrc_03_010
Zrc_60_080
0.97
0.67
0.03
Zrc_11_020
Zrc_91_118
0.35
Zrc_05_012
Zrc_43_060
Th/U
Spot name
0.07353
0.07339
0.07338
0.07337
0.07310
0.07305
0.07260
0.07238
0.06990
0.06911
0.06945
0.07280
0.06990
0.06663
0.06229
0.06169
0.06123
0.06038
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
1.50 1.80820 1.56 0.17811 0.43 0.29
1.40 1.80310 1.48 0.17837 0.48 0.32
1.70 1.86950 1.77 0.18477 0.48 0.26
1.89 1.77680 2.00 0.17588 0.62 0.32
1.50 1.95000 1.57 0.19336 0.46 0.28
1.40 1.83210 1.47 0.18188 0.45 0.31
1.50 1.80690 1.58 0.18029 0.51 0.32
1.20 1.77700 1.29 0.17772 0.46 0.35
1.40 1.59010 1.45 0.16480 0.38 0.26
1.79 1.50930 1.92 0.15840 0.66 0.35
1.50 1.49530 1.56 0.15605 0.44 0.29
1.30 1.51860 1.36 0.15115 0.40 0.28
2.40 1.45090 2.55 0.15050 0.85 0.33
2.00 1.28230 2.09 0.13942 0.60 0.29
1.61 1.01450 1.68 0.11817 0.51 0.29
1.30 0.95914 1.38 0.11267 0.45 0.33
1.31 0.94427 1.35 0.11180 0.36 0.25
1.71 0.89490 1.77 0.10754 0.51 0.28
1σ
1057
1058
1093
1044
1140
1077
1069
1055
983
948
935
907
904
841
720
688
683
658
206 Pb/238 U
4
5
5
6
5
4
5
4
3
6
4
3
7
5
3
3
2
3
1σ
1048
1047
1070
1037
1098
1057
1048
1037
966
934
928
938
910
838
711
683
675
649
207 Pb/235 U
10
10
12
13
11
10
10
8
9
12
10
8
15
12
9
7
7
9
1σ
30
28
34
38
30
27
30
24
28
36
30
26
49
40
34
27
27
36
1029
1025
1024
1024
1017
1015
1003
997
983
948
935
907
904
841
720
688
683
658
30
28
34
38
30
27
30
24
3
6
4
3
7
5
3
3
2
3
1σ Best age 1σ
1029
1025
1024
1024
1017
1015
1003
997
925
902
912
1008
925
826
684
663
647
617
207 Pb/206 U
Ages (Ma)
102
0.38
0.39
0.33
0.43
0.51
Zrc_49_067
Zrc_41_058
Zrc_56_076
0.38
Zrc_24_037
Zrc_32_047
0.64
Zrc_48_066
Zrc_17_027
0.14
0.28
Zrc_15_024
0.48
Zrc_96_124
Zrc_01_008
0.26
0.26
0.18
Zrc_100_128
Zrc_76_100
0.37
Zrc_46_064
Zrc_07_015
0.28
0.37
0.34
Zrc_04_011
Zrc_29_043
0.37
Zrc_54_073
Zrc_85_110
Th/U
Spot name
0.07824
0.07805
0.07782
0.07754
0.07750
0.07740
0.07714
0.07621
0.07503
0.07487
0.07459
0.07446
0.07429
0.07428
0.07402
0.07400
0.07397
0.07374
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
1.30 2.16320 1.35 0.20031 0.38 0.27
1.40 2.18960 1.46 0.20343 0.43 0.30
1.40 2.14040 1.45 0.19923 0.39 0.27
1.70 2.11560 1.77 0.19782 0.50 0.28
1.30 2.11210 1.39 0.19759 0.49 0.35
1.78 1.97396 1.98 0.18496 0.49 0.34
1.59 2.02090 1.68 0.18989 0.51 0.31
1.40 2.05560 1.46 0.19565 0.42 0.28
1.31 2.06560 1.37 0.19965 0.44 0.31
1.50 1.95140 1.57 0.18867 0.48 0.31
1.60 1.83180 1.71 0.17814 0.60 0.36
1.40 1.81370 1.51 0.17651 0.57 0.38
1.31 1.82290 1.35 0.17772 0.37 0.26
1.60 1.87250 1.68 0.18253 0.52 0.31
1.50 1.66500 1.58 0.16303 0.50 0.32
1.50 1.82730 1.56 0.17906 0.43 0.28
1.70 1.86690 1.81 0.18275 0.61 0.33
1.51 1.85490 1.56 0.18238 0.44 0.27
1σ
1177
1194
1171
1164
1162
1094
1121
1152
1173
1114
1057
1048
1055
1081
974
1062
1082
1080
206 Pb/238 U
4
5
4
5
5
5
5
4
5
5
6
6
4
5
5
4
6
4
1σ
1169
1178
1162
1154
1153
1107
1123
1134
1137
1099
1057
1050
1054
1071
995
1055
1069
1065
207 Pb/235 U
9
10
10
12
10
13
11
10
9
11
11
10
9
11
10
10
12
10
1σ
26
27
28
33
26
34
32
27
26
29
31
28
25
32
30
29
33
30
1153
1148
1142
1135
1134
1132
1125
1101
1069
1065
1057
1054
1049
1049
1042
1041
1041
1034
26
27
28
33
26
34
32
27
26
29
31
28
25
32
30
29
33
30
1σ Best age 1σ
1153
1148
1142
1135
1134
1132
1125
1101
1069
1065
1057
1054
1049
1049
1042
1041
1041
1034
207 Pb/206 U
Ages (Ma)
103
0.35
0.43
0.89
0.17
0.47
Zrc_58_078
Zrc_89_115
Zrc_20_030
0.42
Zrc_95_122
Zrc_81_106
0.52
Zrc_90_116
Zrc_26_040
0.26
0.18
Zrc_74_097
0.26
Zrc_61_082
Zrc_82_107
0.30
0.27
0.33
Zrc_28_042
Zrc_50_068
0.29
Zrc_86_112
Zrc_51_070
0.39
0.31
0.26
Zrc_12_021
Zrc_38_054
0.47
Zrc_62_083
Zrc_66_088
Th/U
Spot name
0.17663
0.13691
0.09615
0.09436
0.08608
0.08504
0.08382
0.08243
0.08229
0.08168
0.08167
0.08071
0.08041
0.07959
0.07870
0.07869
0.07868
0.07833
207 Pb/206 Pb
207 Pb/235 U
1σ
206 Pb/238 U
1σ Rho
1.30 12.36600 1.36 0.50743 0.39 0.28
1.20 7.90740 1.25 0.41835 0.36 0.29
1.30 3.82670 1.36 0.28842 0.41 0.30
1.20 3.59280 1.28 0.27652 0.44 0.35
1.41 2.77100 1.49 0.23334 0.52 0.34
1.51 2.76800 1.57 0.23598 0.48 0.29
1.40 2.38840 1.47 0.20643 0.45 0.31
1.30 2.48270 1.63 0.21778 0.98 0.60
1.40 2.50110 1.46 0.22014 0.41 0.29
1.30 2.53490 1.36 0.22502 0.40 0.30
1.80 2.41270 1.89 0.21420 0.57 0.30
1.30 2.44490 1.39 0.21948 0.49 0.35
1.80 2.29120 1.88 0.20596 0.55 0.29
1.29 2.22040 1.36 0.20187 0.41 0.31
1.30 2.27640 1.35 0.20949 0.36 0.28
1.50 2.17290 1.56 0.20003 0.41 0.26
1.30 2.19530 1.37 0.20232 0.43 0.32
1.40 2.20260 1.47 0.20382 0.44 0.29
1σ
2646
2253
1634
1574
1352
1366
1210
1270
1283
1308
1251
1279
1207
1185
1226
1175
1188
1196
206 Pb/238 U
8
7
6
6
6
6
5
11
5
5
6
6
6
4
4
4
5
5
1σ
2633
2221
1598
1548
1348
1347
1239
1267
1272
1282
1246
1256
1210
1187
1205
1172
1180
1182
207 Pb/235 U
13
11
11
10
11
12
11
12
11
10
14
10
13
10
10
11
10
10
1σ
2621
2188
1551
1515
1340
1316
1288
1256
1252
1238
1238
1214
1207
1187
1165
1164
1164
1155
207 Pb/206 U
Ages (Ma)
21
20
24
22
27
28
26
25
27
25
35
25
35
26
25
29
25
27
2621
2188
1551
1515
1340
1316
1288
1256
1252
1238
1238
1214
1207
1187
1165
1164
1164
1155
21
20
24
22
27
28
26
25
27
25
35
25
35
26
25
29
25
27
1σ Best age 1σ
104
0.58
0.94
0.95
0.30
0.69
Zrc_85_108
Zrc_82_105
Zrc_9_017
0.80
Zrc_18_028
Zrc_55_072
0.84
Zrc_65_084
Zrc_70_090
0.49
0.89
Zrc_71_092
0.64
Zrc_53_070
Zrc_90_114
0.44
0.46
0.50
Zrc_38_052
Zrc_54_071
0.58
Zrc_75_096
Zrc_30_042
0.36
0.28
0.20
Zrc_16_026
Zrc_04_011
0.21
Zrc_72_093
Zrc_46_062
Th/U
Spot name
0.05649
0.05504
0.05606
0.05372
0.05634
0.05617
0.05545
0.05734
0.05718
0.05365
0.05983
0.05899
0.05778
0.05633
0.05429
0.05727
0.05518
0.05389
207 Pb/206 Pb
207 Pb/235 U
2.00 0.38197
1.71 0.37161
1.80 0.37698
1.51 0.36164
2.59 0.37782
2.71 0.37713
1.70 0.37143
2.30 0.38220
3.39 0.37909
1.30 0.35678
5.20 0.39736
3.31 0.38845
4.29 0.38198
2.70 0.37081
1.81 0.35668
4.30 0.36897
2.59 0.35042
1.21 0.33885
1σ
2.05
1.77
1.85
1.58
2.66
2.73
1.78
2.34
3.45
1.36
5.25
3.36
4.34
2.78
1.87
4.33
2.63
1.27
1σ
1σ Rho
0.04932 0.49 0.22
0.04920 0.53 0.25
0.04909 0.45 0.22
0.04910 0.45 0.30
0.04886 0.51 0.23
0.04896 0.47 0.14
0.04885 0.41 0.30
0.04865 0.49 0.19
0.04856 0.68 0.18
0.04845 0.43 0.29
0.04823 1.22 0.14
0.04808 0.62 0.18
0.04809 0.77 0.15
0.04795 0.60 0.24
0.04788 0.52 0.26
0.04685 1.66 0.12
0.04627 1.62 0.18
0.04584 0.48 0.32
206 Pb/238 U
310
310
309
309
308
308
307
306
306
305
304
303
303
302
301
295
292
289
206 Pb/238 U
1
1
1
2
2
1
2
1
2
1
2
2
2
2
1
1
1
1
1σ
328
321
325
313
325
325
321
329
326
310
340
333
328
320
310
319
305
296
207 Pb/235 U
6
5
5
4
7
8
5
7
10
4
15
10
12
8
5
12
7
3
1σ
41
36
37
32
58
59
35
47
70
29
112
72
95
56
41
95
57
25
310
310
309
309
308
308
307
306
306
305
304
303
303
302
301
295
292
289
1
1
1
2
2
1
2
1
2
1
2
2
2
2
1
1
1
1
1σ Best age 1σ
472
414
455
359
466
459
430
505
499
356
597
567
521
465
383
502
420
366
207 Pb/206 U
Ages (Ma)
105
0.48
0.66
0.83
1.08
0.79
Zrc_31_044
Zrc_58_076
Zrc_59_077
0.58
Zrc_66_086
Zrc_57_075
0.54
Zrc_14_023
Zrc_76_098
0.57
0.48
Zrc_48_064
0.47
Zrc_10_018
Zrc_56_074
0.82
0.64
0.41
Zrc_05_012
Zrc_08_016
0.73
Zrc_27_039
Zrc_29_041
0.72
0.41
0.84
Zrc_3_010
Zrc_35_048
0.87
Zrc_96_122
Zrc_17_027
Th/U
Spot name
0.05339
0.05831
0.05524
0.05442
0.05653
0.06054
0.05746
0.06271
0.05872
0.05429
0.05862
0.06046
0.05860
0.05589
0.05818
0.06166
0.05937
0.05427
207 Pb/206 Pb
207 Pb/235 U
2.85
1.38
1σ
1σ Rho
0.04948 1.52 0.20
0.04921 0.39 0.31
206 Pb/238 U
1.59 0.37961
1.70 0.41377
1.50 0.39019
1.40 0.37887
2.00 0.39302
3.04 0.42154
3.10 0.39806
4.10 0.43288
3.00 0.40509
1.60 0.37429
3.51 0.40481
2.50 0.41720
3.60 0.40379
1.50 0.38223
2.70 0.39696
1.67
1.85
1.56
1.46
2.09
3.38
3.14
4.15
3.07
1.69
3.84
2.56
3.67
1.56
2.76
0.05188 0.44 0.30
0.05176 0.66 0.40
0.05153 0.41 0.26
0.05081 0.41 0.30
0.05065 0.67 0.29
0.05050 0.20 0.28
0.05055 0.77 0.17
0.05025 1.23 0.16
0.05021 0.68 0.22
0.05016 0.50 0.32
0.05009 0.20 0.22
0.05010 0.96 0.21
0.05014 1.18 0.19
0.04983 0.42 0.26
0.04973 0.64 0.21
9.78 0.41989 10.40 0.04939 0.34 0.14
2.80 0.40403
1.31 0.36648
1σ
326
325
324
319
319
318
318
316
316
316
315
315
315
313
313
311
311
310
206 Pb/238 U
1
2
1
1
2
2
2
2
2
2
2
2
2
1
2
3
2
1
1σ
327
352
335
326
337
357
340
365
345
323
345
354
344
329
339
356
345
317
207 Pb/235 U
5
6
4
4
6
10
9
13
9
5
11
8
11
4
8
31
8
4
1σ
34
35
34
29
41
61
67
81
66
35
71
50
79
33
58
216
60
27
326
325
324
319
319
318
318
316
316
316
315
315
315
313
313
311
311
310
1
2
1
1
2
2
2
2
2
2
2
2
2
1
2
3
2
1
1σ Best age 1σ
345
541
422
388
473
623
509
698
557
383
553
620
552
448
537
662
581
382
207 Pb/206 U
Ages (Ma)
106
0.14
1.10
0.81
0.16
0.47
Zrc_01_008
Zrc_44_059
Zrc_84_107
0.93
Zrc_19_029
Zrc_39_053
0.86
Zrc_45_060
Zrc_74_095
0.17
0.95
Zrc_40_054
0.86
Zrc_91_116
Zrc_97_123
0.68
0.17
0.80
Zrc_63_082
Zrc_21_032
0.18
Zrc_28_040
Zrc_86_110
0.37
0.07
0.59
Zrc_81_104
Zrc_78_100
0.17
Zrc_50_066
Zrc_02_009
Th/U
Spot name
0.06505
0.07168
0.06155
0.06208
0.06077
0.06058
0.06121
0.06320
0.06384
0.06142
0.05801
0.05957
0.05851
0.05831
0.05768
0.05769
0.06033
0.05492
207 Pb/206 Pb
207 Pb/235 U
0.81 1.05840
1.31 1.16140
1.80 0.86568
1.30 0.85890
1.00 0.82630
1.40 0.81873
0.78 0.81920
2.10 0.83165
2.30 0.83905
1.81 0.73327
1.29 0.64989
1.49 0.66855
1.01 0.60660
2.09 0.54341
3.69 0.43409
1.99 0.43182
2.70 0.44036
2.02 0.40183
1σ
0.92
1.88
1.86
1.38
1.07
1.46
0.97
2.19
2.36
1.89
1.38
1.58
1.08
2.16
3.76
2.07
2.79
2.27
1σ
1σ Rho
0.11845 0.41 0.46
0.11752 0.32 0.67
0.10234 0.43 0.23
0.10092 0.41 0.32
0.09894 0.59 0.34
0.09846 0.58 0.28
0.09741 0.40 0.59
0.09625 0.47 0.28
0.09582 1.34 0.21
0.08703 0.47 0.30
0.08168 0.59 0.34
0.08166 0.47 0.33
0.07553 0.38 0.37
0.06790 0.87 0.25
0.05486 3.74 0.19
0.05458 0.68 0.27
0.05321 0.60 0.24
0.05307 0.23 0.37
206 Pb/238 U
722
716
628
620
608
605
599
592
590
538
506
506
469
423
344
343
334
333
206 Pb/238 U
3
7
3
3
2
2
3
4
3
3
2
2
2
2
2
2
2
2
1σ
733
783
633
630
612
607
608
615
619
558
508
520
481
441
366
364
371
343
207 Pb/235 U
5
10
9
6
5
7
4
10
11
8
6
6
4
8
12
6
9
7
1σ
16
27
38
26
22
30
17
41
49
36
26
32
20
45
80
41
54
46
722
716
628
620
608
605
599
592
590
538
506
506
469
423
344
343
334
333
3
7
3
3
2
2
3
4
3
3
2
2
2
2
2
2
2
2
1σ Best age 1σ
776
977
659
677
631
624
647
715
736
654
530
588
549
541
518
518
615
409
207 Pb/206 U
Ages (Ma)
107
0.19
0.08
0.30
0.27
0.56
Zrc_62_081
Zrc_69_089
Zrc_37_051
0.25
Zrc_07_015
Zrc_93_118
0.40
Zrc_11_020
Zrc_99_125
0.08
0.25
Zrc_89_113
0.29
Zrc_49_065
Zrc_36_050
0.60
0.17
0.29
Zrc_100_126
Zrc_80_102
0.34
Zrc_77_099
Zrc_87_111
0.18
0.27
0.09
Zrc_95_120
Zrc_34_047
0.42
Zrc_61_080
Zrc_22_033
Th/U
Spot name
0.07691
0.07679
0.07667
0.07661
0.07645
0.07634
0.07562
0.07542
0.07511
0.07486
0.07470
0.07369
0.07365
0.07304
0.07302
0.07147
0.07172
0.06532
207 Pb/206 Pb
207 Pb/235 U
1.00 2.03680
0.76 1.85840
1.70 1.91840
4.33 1.69231
1.50 1.88460
0.81 2.05100
1.90 1.67720
1.50 1.85100
0.67 1.74223
1.40 1.84820
3.76 1.65148
0.83 1.73970
1.10 1.74530
1.00 1.67330
0.97 1.83130
0.80 1.59700
0.73 1.56330
2.01 1.09070
1σ
1.09
0.92
1.77
4.65
1.58
0.92
1.94
1.70
0.80
1.46
3.97
0.90
1.18
1.10
1.07
1.10
0.84
2.07
1σ
1σ Rho
0.19275 0.40 0.39
0.17628 0.39 0.57
0.18239 0.58 0.29
0.16022 0.37 0.25
0.18000 0.67 0.31
0.19539 0.44 0.46
0.16158 0.58 0.19
0.17859 0.60 0.48
0.16823 0.12 0.52
0.17987 0.53 0.28
0.16035 0.23 0.21
0.17204 0.37 0.40
0.17276 0.40 0.37
0.16688 0.41 0.42
0.18246 0.42 0.42
0.16253 0.70 0.69
0.15883 0.51 0.50
0.12169 0.44 0.25
206 Pb/238 U
1136
1047
1080
958
1067
1151
966
1059
1002
1066
959
1023
1027
995
1080
971
950
740
206 Pb/238 U
4
5
5
8
5
5
3
8
4
4
6
3
4
4
4
7
4
4
1σ
1128
1066
1088
1006
1076
1133
1000
1064
1024
1063
990
1023
1025
998
1057
969
956
749
207 Pb/235 U
7
6
12
30
11
6
12
11
5
10
25
6
8
7
7
7
5
11
1σ
20
14
32
80
28
15
38
30
12
28
70
16
22
19
19
16
14
39
1119
1116
1113
1111
1107
1104
1085
1080
1071
1065
1060
1033
1032
1015
1015
971
950
740
20
14
32
80
28
15
38
30
12
28
70
16
22
19
19
7
4
4
1σ Best age 1σ
1119
1116
1113
1111
1107
1104
1085
1080
1071
1065
1060
1033
1032
1015
1015
971
978
785
207 Pb/206 U
Ages (Ma)
108
0.46
0.32
0.39
0.16
0.29
Zrc_67_087
Zrc_23_034
Zrc_60_078
0.27
Zrc_79_101
Zrc_42_057
0.30
Zrc_51_068
Zrc_94_119
0.32
1.25
Zrc_13_022
0.21
Zrc_52_069
Zrc_24_035
0.77
0.69
0.14
Zrc_15_024
Zrc_26_038
0.31
Zrc_68_088
Zrc_41_056
0.14
0.39
0.26
Zrc_92_117
Zrc_25_036
0.44
Zrc_06_014
Zrc_83_106
Th/U
Spot name
0.08838
0.08707
0.08671
0.08331
0.08320
0.08164
0.08149
0.08118
0.08093
0.08036
0.08034
0.07889
0.07868
0.07836
0.07809
0.07795
0.07764
0.07745
207 Pb/206 Pb
207 Pb/235 U
1.10 2.94340
0.88 2.96060
1.20 2.75830
1.30 2.48507
1.90 2.35750
0.75 2.46650
0.99 2.19990
1.40 2.30770
0.80 2.33510
0.71 2.32090
1.10 2.24590
0.99 2.16210
1.19 2.22340
1.60 1.98340
1.10 1.85520
1.10 2.06240
1.80 1.91530
1.39 1.93080
1σ
1.20
0.98
1.29
1.60
1.96
0.84
1.09
1.49
0.88
0.81
1.18
1.06
1.28
1.67
1.17
1.16
1.90
1.51
1σ
1σ Rho
0.24281 0.60 0.40
0.24754 0.52 0.43
0.23164 0.42 0.37
0.21634 0.17 0.52
0.20632 0.66 0.26
0.22016 0.37 0.46
0.19660 0.43 0.41
0.20681 0.36 0.33
0.20985 0.37 0.41
0.21013 0.38 0.48
0.20370 0.48 0.37
0.19936 0.37 0.37
0.20589 0.86 0.36
0.18431 0.74 0.30
0.17298 0.40 0.34
0.19270 1.36 0.32
0.17986 0.72 0.32
0.18142 0.60 0.39
206 Pb/238 U
1401
1426
1343
1262
1209
1283
1157
1212
1228
1230
1195
1172
1207
1090
1029
1136
1066
1075
206 Pb/238 U
6
5
6
7
6
4
5
6
4
4
5
4
5
5
4
4
6
6
1σ
1393
1398
1344
1268
1230
1262
1181
1215
1223
1219
1196
1169
1188
1110
1065
1136
1086
1092
207 Pb/235 U
9
7
10
12
14
6
8
11
6
6
8
7
9
11
8
8
13
10
1σ
20
17
22
23
37
14
20
27
16
14
22
19
23
29
20
22
33
26
1391
1362
1354
1277
1274
1237
1233
1226
1220
1206
1205
1169
1164
1156
1149
1146
1138
1133
20
17
22
23
37
14
20
27
16
14
22
19
23
29
20
22
33
26
1σ Best age 1σ
1391
1362
1354
1277
1274
1237
1233
1226
1220
1206
1205
1169
1164
1156
1149
1146
1138
1133
207 Pb/206 U
Ages (Ma)
109
0.48
Zrc_98_124
0.74
0.52
0.26
0.33
0.25
0.49
Zrc_36_050
Zrc_11_020
Zrc_02_009
Zrc_29_041
0.05833
0.05287
0.05486
0.05540
0.06017
0.05497
207 Pb/206 Pb
0.06140
Zrc_6_014
207 Pb/235 U
0.96
0.94
0.94
0.78
1σ
0.72 12.10500 0.91
0.71 5.96711
0.80 5.04420
0.76 3.55300
0.69 3.75430
1σ
1σ Rho
0.47398 0.36 0.61
0.31884 0.16 0.64
0.32637 0.37 0.53
0.26508 0.43 0.59
0.28104 0.35 0.46
206 Pb/238 U
2501
1784
1821
1516
1597
206 Pb/238 U
12
9
8
7
5
1σ
2613
1971
1827
1539
1583
207 Pb/235 U
9
8
8
7
6
1σ
2708
2173
1836
1580
1571
207 Pb/206 U
Ages (Ma)
4.92
1.10
2.21
2.47
1.65
1.80
2.31
1σ
0.38249
0.34621
0.35656
0.35680
0.38366
0.34950
0.38560
207 Pb/235 U
5.26
1.20
2.27
2.69
2.01
1.87
2.57
1σ
1σ Rho
0.04756 0.86 0.24
0.04739 0.46 0.40
0.04707 0.55 0.23
0.04671 0.64 0.30
0.04625 0.65 0.43
0.04607 0.50 0.27
0.04555 0.53 0.40
206 Pb/238 U
300
298
297
294
291
290
287
206 Pb/238 U
3
1
2
2
2
1
1
1σ
329
302
310
310
330
304
331
207 Pb/235 U
15
3
6
7
6
5
7
1σ
2708
2173
1836
1580
1571
11
12
15
13
13
107
24
48
55
35
36
48
1
300
298
297
294
3
1
2
2
2
290
291
1
287
1σ Best age 1σ
11
12
15
13
13
1σ Best age 1σ
542
323
407
428
610
411
653
207 Pb/206 U
Ages (Ma)
Tabla 8: LA-ICP-MS U-Pb isotopic data for Tecomate Formation granite dike TT-615.
0.18609
0.13573
0.11227
0.09764
0.09720
207 Pb/206 Pb
0.46
Zrc_31_044
Zrc_24_035
Spot name Th/U
0.36
0.18
0.40
Zrc_64_083
Zrc_47_063
0.58
Zrc_43_058
Zrc_32_045
Th/U
Spot name
110
0.59
0.69
0.71
0.56
0.53
Zrc_38_052
Zrc_50_066
Zrc_64_083
0.46
Zrc_05_012
Zrc_65_084
0.95
Zrc_60_078
Zrc_18_028
0.52
0.66
Zrc_17_027
0.53
Zrc_16_026
Zrc_57_075
0.69
0.49
0.44
Zrc_46_062
Zrc_15_024
0.51
Zrc_51_068
Zrc_25_036
0.53
0.52
Zrc_66_086
1.37
Zrc_35_048
Zrc_45_060
0.33
Zrc_71_091
Spot name Th/U
0.06188
0.05692
0.05299
0.06230
0.05690
0.06045
0.06124
0.06154
0.05839
0.05738
0.05970
0.05625
0.05472
0.05338
0.05204
0.05140
0.05502
0.05919
207 Pb/206 Pb
4.02
1.70
1.40
2.30
3.01
9.78
1.50
2.39
3.10
4.98
1.89
1.30
2.25
0.94
1.19
1.11
1.11
2.50
1σ
1.56
2.66
3.30
5.20
2.19
1.37
2.45
1.01
1.28
1.18
1.56
3.07
1σ
1σ Rho
0.04940 0.45 0.28
0.04950 0.65 0.30
0.04948 0.57 0.20
0.04945 0.55 0.12
0.04912 1.10 0.51
0.04902 0.45 0.32
0.04853 0.54 0.24
0.04829 0.39 0.38
0.04812 0.44 0.36
0.04795 0.42 0.33
0.04785 1.11 0.70
0.04757 1.05 0.59
206 Pb/238 U
0.43071
0.39463
0.36576
0.42648
0.38823
4.23
1.77
1.45
2.50
3.05
0.05048 0.73 0.21
0.05032 0.50 0.27
0.04995 0.36 0.27
0.04969 0.97 0.39
0.04956 0.52 0.17
0.41312 10.08 0.04957 0.99 0.12
0.41793
0.42005
0.39833
0.39120
0.40508
0.38052
0.36611
0.35617
0.34569
0.34080
0.36306
0.38825
207 Pb/235 U
317
316
314
313
312
312
311
311
311
311
309
309
305
304
303
302
301
300
206 Pb/238 U
2
2
1
3
2
3
1
2
2
2
3
1
2
1
1
1
3
3
1σ
364
338
317
361
333
351
355
356
340
335
345
327
317
309
301
298
314
333
207 Pb/235 U
13
5
4
8
9
30
5
8
10
15
6
4
7
3
3
3
4
9
1σ
78
34
31
47
60
192
29
46
65
107
40
28
50
19
27
23
24
53
317
316
314
313
312
312
311
311
311
311
309
309
305
304
303
302
301
300
2
2
1
3
2
3
1
2
2
2
3
1
2
1
1
1
3
3
1σ Best age 1σ
670
488
328
684
488
620
648
658
544
506
593
462
401
345
287
259
413
574
207 Pb/206 U
Ages (Ma)
111
0.70
0.65
0.37
0.60
0.19
Zrc_32_045
Zrc_08_016
Zrc_03_010
0.71
Zrc_54_071
Zrc_43_058
1.06
Zrc_21_032
Zrc_30_042
0.57
0.64
Zrc_33_046
0.42
Zrc_59_077
Zrc_34_047
0.98
0.93
0.45
Zrc_01_008
Zrc_28_040
0.74
Zrc_62_081
Zrc_39_053
0.51
0.51
Zrc_44_059
0.63
Zrc_56_074
Zrc_63_082
0.58
Zrc_37_051
Spot name Th/U
0.06081
0.06104
0.06381
0.06172
0.05997
0.07700
0.05513
0.05346
0.05957
0.05663
0.05445
0.05960
0.05239
0.05546
0.05759
0.05950
0.06185
0.05377
207 Pb/206 Pb
0.40522
0.38954
0.43257
0.40520
0.38780
0.42406
0.37292
0.39395
0.40739
0.42047
0.43471
0.37555
207 Pb/235 U
1.62
1.59
4.45
3.14
1.95
5.11
1.36
1.18
1.67
1.49
2.48
1.35
1σ
1σ Rho
0.05333 0.81 0.50
0.05277 0.53 0.34
0.05266 0.74 0.19
0.05189 0.60 0.21
0.05156 0.45 0.25
0.05161 0.83 0.26
0.05157 0.41 0.30
0.05143 0.43 0.36
0.05119 0.47 0.29
0.05121 0.51 0.35
0.05100 0.61 0.26
0.05057 0.36 0.26
206 Pb/238 U
1.91
1.00
1.30
1.30
1.80
0.76649
0.75047
0.76548
0.69836
0.47709
1.98
1.06
1.35
1.42
1.93
0.09149 0.55 0.26
0.08905 0.36 0.34
0.08690 0.38 0.28
0.08196 0.56 0.40
0.05750 0.71 0.37
11.87 0.56717 12.44 0.05342 1.55 0.18
1.40
1.50
4.18
3.00
1.89
4.65
1.30
1.10
1.60
1.39
2.39
1.30
1σ
564
550
537
508
360
335
335
332
331
326
324
324
324
323
322
322
321
318
206 Pb/238 U
3
2
2
3
2
5
3
2
2
2
1
3
1
1
1
2
2
1
1σ
578
568
577
538
396
456
345
334
365
345
333
359
322
337
347
356
367
324
207 Pb/235 U
9
5
6
6
6
46
5
5
14
9
6
15
4
3
5
4
8
4
1σ
41
21
27
27
39
216
30
33
90
60
42
100
29
22
32
30
46
29
564
550
537
508
360
335
335
332
331
326
324
324
324
323
322
322
321
318
3
2
2
3
2
5
3
2
2
2
1
3
1
1
1
2
2
1
1σ Best age 1σ
633
641
735
664
603
1121
417
348
588
477
390
589
302
431
514
585
669
361
207 Pb/206 U
Ages (Ma)
112
0.33
0.48
0.35
0.24
0.30
Zrc_42_057
Zrc_70_090
Zrc_23_034
0.27
Zrc_55_072
Zrc_72_092
0.25
Zrc_09_017
Zrc_13_022
0.12
0.27
Zrc_48_064
0.55
Zrc_22_033
Zrc_47_063
0.07
0.42
0.15
Zrc_41_056
Zrc_10_018
0.18
Zrc_69_089
Zrc_04_011
0.21
0.44
Zrc_20_030
0.56
Zrc_58_076
Zrc_52_069
0.28
Zrc_26_038
Spot name Th/U
0.08120
0.08088
0.08019
0.08008
0.07980
0.07979
0.07948
0.07936
0.07509
0.07468
0.07460
0.07042
0.07233
0.07176
0.07966
0.06162
0.06191
0.06385
207 Pb/206 Pb
0.76
1.22
1.40
0.87
1.00
0.95
0.81
0.84
1.31
1.10
1.30
0.70
1.30
0.72
1.41
0.86
1.10
1.10
1σ
2.48890
1.99665
2.19080
2.21090
2.18680
2.25060
2.25320
2.26080
1.85500
1.89970
1.82970
1.60680
1.64720
1.44983
1.42970
0.88174
0.82188
0.80779
207 Pb/235 U
0.82
1.37
1.58
0.95
1.09
1.01
0.91
0.91
1.38
1.19
1.35
0.75
1.37
0.83
1.59
0.94
1.17
1.18
1σ
1σ Rho
0.22198 0.30 0.36
0.17904 0.47 0.35
0.19815 0.49 0.34
0.19987 0.39 0.40
0.19836 0.44 0.40
0.20416 0.33 0.32
0.20512 0.42 0.47
0.20618 0.32 0.37
0.17900 0.45 0.32
0.18427 0.46 0.39
0.17737 0.37 0.27
0.16512 0.30 0.38
0.16483 0.44 0.32
0.14652 0.32 0.42
0.12952 0.75 0.47
0.10365 0.38 0.40
0.09614 0.41 0.35
0.09158 0.44 0.38
206 Pb/238 U
1292
1062
1165
1175
1167
1198
1203
1208
1062
1090
1053
985
984
881
785
636
592
565
206 Pb/238 U
4
5
5
4
5
4
5
4
4
5
4
3
4
3
6
2
2
2
1σ
1269
1114
1178
1184
1177
1197
1198
1200
1065
1081
1056
973
988
910
901
642
609
601
207 Pb/235 U
6
9
11
7
8
7
6
6
9
8
9
5
9
5
9
4
5
5
1σ
14
24
27
17
19
17
16
15
24
21
26
14
26
14
25
18
21
23
1226
1219
1202
1199
1192
1192
1184
1181
1071
1060
1058
985
984
881
785
636
592
565
14
24
27
17
19
17
16
15
24
21
26
3
4
3
6
2
2
2
1σ Best age 1σ
1226
1219
1202
1199
1192
1192
1184
1181
1071
1060
1058
941
995
979
1189
661
671
737
207 Pb/206 U
Ages (Ma)
113
0.54
0.21
Zrc_14_023
Zrc_27_039
0.17580
0.15203
0.09430
0.08614
0.08525
0.08171
0.08142
207 Pb/206 Pb
8.48473
3.48900
2.18640
2.56850
2.45490
2.22243
207 Pb/235 U
0.88
0.87
1.31
1.26
0.81
1.58
1σ
1σ Rho
0.43707 0.43 0.52
0.40476 0.45 0.60
0.26789 0.35 0.41
0.18376 0.53 0.41
0.21851 0.96 0.79
0.21745 0.35 0.42
0.19796 0.56 0.40
206 Pb/238 U
2338
2191
1530
1087
1274
1268
1164
206 Pb/238 U
8
8
5
5
11
4
6
1σ
2488
2284
1525
1177
1292
1259
1188
207 Pb/235 U
0.00
6.01
0.78
0.08
698.13
583.65
Zrc_05_012 302
Zrc_02_009 301
Zrc_21_032 299
Zrc_47_063 286
1.20
767.48
1.38
1.13
Zrc_57_075 285
13.42
0.70
Zrc_52_069 285
7.93
-0.33
0.66
1.64
Zrc_19_029 299
811.54
0.36
Zrc_56_074 278
1.33
TT-72 (Hornblende Gabbro)
21.18
2614
2369
1514
1341
1321
1239
1232
207 Pb/206 U
11
10
14
21
13
14
25
2614
2369
1514
1341
1321
1239
1232
11
10
14
21
13
14
25
1σ Best age 1σ
0.96
1.28
0.78
0.51
733.02
800.54
697.61
651.04
9.13
18.97
5.97
3.25
Age Concordance Ti (ppm) log(Ti) T (◦ C)
TT-76B (Quartz Diorite)
Sample
8
8
7
9
9
6
11
1σ
Ages (Ma)
Tabla 9: Ti-in-zircon thermometry for rocks of the Totoltepec pluton.
0.70 10.59397 0.86
0.63
0.80
1.20
0.75
0.73
1.41
1σ
0.65
Zrc_12_021
Sample
0.10
0.78
Zrc_49_065
0.36
Zrc_40_054
Zrc_61_080
0.29
Zrc_53_070
Spot name Th/U
114
1.03
-0.70
0.34
3.67
2.03
3.02
-0.69
0.34
1.36
0.34
1.01
1.68
0.00
Zrc_74_095 288
Zrc_46_062 289
Zrc_64_083 289
Zrc_69_089 289
Zrc_78_100 289
Zrc_72_093 290
Zrc_48_064 291
Zrc_55_072 291
Zrc_58_076 292
Zrc_68_088 293
Zrc_75_096 293
Zrc_77_099 293
12.04
6.04
9.14
2.04
22.78
14.48
7.62
1.01
20.83
12.41
6.88
9.13
3.66
1.08
0.78
0.96
0.31
1.36
1.16
0.88
0.01
1.32
1.09
0.84
0.96
0.56
0.30
757.58
698.49
733.16
618.06
818.88
774.61
717.59
573.16
809.86
760.32
709.09
733.04
659.74
617.09
Zrc_29_040 308
Zrc_13_022 307
Zrc_27_038 306
Zrc_22_033 306
Zrc_16_026 306
Zrc_12_021 306
Zrc_08_016 306
Zrc_07_015 306
Zrc_32_044 305
Zrc_35_046 304
Zrc_04_011 304
Zrc_38_050 303
Zrc_03_010 303
Zrc_01_008 303
Zrc_17_027 302
Zrc_70_090 288
2.01
645.14
2.71
0.48
Zrc_59_077 287
3.00
-1.99
2.54
2.55
-0.99
3.77
2.24
0.97
1.61
2.87
-0.33
2.25
-1.34
3.50
1.62
1.31
5.33
4.03
598.65
Zrc_79_101 286
0.18
Zrc_10_018 302
1.52
1.72
0.95
1.21
1.01
0.98
0.89
0.74
1.20
0.64
0.69
0.75
0.86
1.13
0.78
1.15
0.75
0.63
730.82
784.29
742.65
737.47
719.01
691.12
783.12
672.41
682.53
693.29
712.65
767.85
699.05
771.62
693.14
670.43
8.90
16.04
10.19
9.61
7.75
5.51
15.85
4.33
4.94
5.66
7.18
13.47
6.08
14.03
5.65
4.22
Zrc_76_098 286
Sample
Sample
115
1.00
-0.33
-1.01
-0.99
1.27
Zrc_51_068 300
Zrc_62_081 301
Zrc_73_094 307
Zrc_45_060 310
76.04
STDEV
760.62
574.06
806.24
699.74
746.19
713.34
1.10
0.01
1.30
0.79
1.03
628.83
MEDIAN
12.45
1.03
20.09
6.13
10.61
0.38
4.01
Zrc_15_024 311
STDEV
MEDIAN
3.12
0.64
6.34
8.28
0.32
0.32
2.52
Zrc_11_020 311
Zrc_41_053 310
Zrc_26_037 310
Zrc_06_014 310
Zrc_36_048 309
Zrc_30_041 309
Zrc_20_030 309
Zrc_71_092 297
2.38
730.61
-0.68
0.95
Zrc_53_070 295
8.88
1.28
1.01
666.95
Zrc_50_066 295
0.61
Zrc_37_049 308
4.03
1.01
10.26
1.25
16.02
11.12
7.37
14.88
14.84
7.94
14.40
1.01
0.10
1.20
1.05
0.87
1.17
1.17
0.90
1.16
48.77
730.82
743.27
586.28
784.18
750.38
714.83
777.18
776.91
721.05
774.04
Zrc_80_102 294
Sample
Sample
116
C
TA B L A S G E O Q U Í M I C A
M., Keppie, J.D., Murphy, J.B., y Solari, L.A., 2012, Permian–Carboniferous
arc magmatism and basin evolution along the western margin of Pangea:
geochemical and geochronological evidence from the eastern Acatlán
Complex, southern Mexico: Geological Society of America Bulletin, en
prensa, doi: 10.1130/B30649.1.
117
0.03
0.70
2.69
5.49
0.70
0.07
1.07
100.0
42.9
29
10
4
5
MnO
MgO
CaO
Na2 O
K2 O
P2 O5
LOI
Total
Mg#
V (ppm)
Cr
Co
Ni
18
1.66
Fe2 O3
Ga
16.8
Al2 O3
2
0.23
TiO2
41
70.6
SiO2 (wt %)
Zn
289
Age (Ma)
Cu
trondhj.
Lithology
15
7
1
5
1
15
10
53.5
100.0
0.32
0.01
0.25
5.44
2.19
0.11
0.022
0.17
13.9
0.10
77.5
289
-97.8837
Qz granitoid
-97.85943
Lon
TT-12
18.214116
TT-11
18.228366
Lat
Name
TT-13B
TT-14
TT-15
14
68
104
7
17
2
166
37.7
100.0
0.75
0.10
0.48
3.72
6.69
2.79
0.147
8.22
16.3
0.61
60.2
289
tonal.
16
104
58
8
27
0
288
37.9
100.0
1.02
0.09
0.42
3.62
7.03
3.98
0.225
11.6
15.8
0.76
55.4
289
tonal.
26
55
11
9
13
7
111
43.2
100.0
1.02
0.25
0.22
5.22
9.65
2.43
0.071
5.70
23.6
0.78
51.1
289
hbl diorite
TT-16
TT-18
18
43
1
5
4
12
27
48.9
98.2
1.28
0.10
1.14
4.12
4.62
6.13
0.19
11.4
16.2
0.72
52.3
289
tonal.
18
39
2
5
5
10
28
51.1
99.5
1.22
0.06
1.28
6.20
1.06
0.54
0.041
0.92
15.0
0.19
73.1
289
trondhj.
-97.9005
TT-20
18.260233
TT-22
18.263016
15
19
1
6
3
16
24
42.7
100.4
1.71
0.07
1.00
5.97
2.30
0.67
0.036
1.60
16.7
0.24
70.1
306
trondhj.
15
21
1
5
4
13
22
34.8
100.0
2.60
0.05
0.76
5.55
2.40
0.33
0.041
1.10
15.3
0.17
71.7
289
trondhj.
TT-24
14
66
23
76
43
263
150
64.7
100.0
3.77
0.01
1.35
1.99
8.63
8.36
0.149
8.13
21.3
0.31
46.0
306
hbl gabbro
-97.7994
18.278833
16
51
6
10
8
27
65
52.6
100.0
2.16
0.11
1.16
5.48
2.23
1.84
0.076
2.95
16.1
0.31
67.6
306
trondhj.
-97.850533 -97.838633 -97.832433
18.223066 18.222766 18.257383
-97.88385 -97.88385 -97.890866 -97.899783
18.214033 18.214033 18.208433
TT-13A
Tabla 10: Chemical results for rocks of the Totoltepec Pluton. Acatlán Complex, Puebla, Mexico (part 1/3).
tablas geoquímica
118
9.7
1.2
6.1
1.4
0.6
2.0
0.26
1.9
0.39
2.7
0.3
0.9
0.2
0.2
0.3
0.07
0.4
0.09
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
1.2
0.18
1.2
0.4
0.06
0.4
Er
Tm
Yb
11.8
Ce
261
124
4.4
Cs
1.5
0.0
Ba
2.0
0.1
La
527
Nb
9
59
3
42
287
9
289
tonal.
4.3
0.0
Zr
TT-13B
TT-14
TT-15
3.1
0.49
3.1
1.03
4.7
0.69
4.0
0.8
2.8
9.5
2.2
15.4
6.4
0.3
182
3.6
48
26
265
8
289
tonal.
0.5
0.08
0.6
0.23
1.3
0.26
1.9
0.9
2.1
8.7
1.5
8.9
3.5
0.0
115
1.3
69
6
1129
0
289
hbl diorite
TT-16
TT-18
9.0
1.8
559
0.0
73
4
691
27
289
tonal.
0.3
0.07
0.2
0.11
0.5
0.09
0.5
0.2
0.5
1.6
0.4
3.7
1.8
0.0
400
1.1
75
2
629
27
289
trondhj.
-97.9005
TT-20
18.260233
TT-22
18.263016
12.4
0.0
780
0.0
45
8
328
30
306
trondhj.
6.6
0.0
477
0.0
46
8
323
17
289
trondhj.
TT-24
0.8
0.08
0.6
0.19
1.0
0.13
0.6
0.4
0.6
1.2
0.3
1.9
0.9
8.7
836
0.1
3
5
401
28
306
hbl gabbro
-97.7994
18.278833
0.8
0.09
0.9
0.28
1.3
0.22
1.4
0.4
1.8
7.1
1.6
12.8
6.3
0.0
1404
2.4
57
7
569
25
306
trondhj.
-97.850533 -97.838633 -97.832433
18.223066 18.222766 18.257383
-97.88385 -97.88385 -97.890866 -97.899783
331
3
TT-13A
18.214033 18.214033 18.208433
1.8
4
73
Y
14
708
Sr
289
Age (Ma)
Rb
trondhj.
Lithology
289
-97.8837
Qz granitoid
-97.85943
Lon
TT-12
18.214116
TT-11
18.228366
Lat
Name
tablas geoquímica
119
1.2
0.05
3.9
0.00
Ta
Pb
TT-14
TT-15
1.7
1.4
9.3
0.10
1.3
0.48
289
tonal.
0.0
0.1
0.0
0.03
1.5
0.07
289
hbl diorite
TT-16
TT-18
0.3
0.0
289
tonal.
0.0
0.2
0.0
0.03
1.7
0.04
289
trondhj.
-97.9005
TT-20
18.260233
TT-22
18.263016
0.2
2.0
306
trondhj.
1.9
5.0
289
trondhj.
0.0
1.0
4.4
0.04
1.3
0.08
306
trondhj.
-97.850533 -97.838633 -97.832433
18.223066 18.222766 18.257383
TT-24
71.6
0.18
15.7
1.19
SiO2 (wt %)
Al2 O3
Fe2 O3
289
Age (Ma)
TiO2
trondhj.
Lithology
TT-26B
-97.78115
18.2597
2.79
29.5
0.18
44.7
306
7.55
19.1
0.24
47.3
306
hbl leucogabbro hbl gabbro
-97.78115
-97.788783
Lon
TT-26A
18.2597
TT-25
18.266666
TT-27
TT-28
TT-49
18.260116 18.229316
TT-50
TT-51
18.232683 18.235433
TT-52
18.2292
TT-53
18.2203
18.220783
0.28
14.6
0.11
75.7
306
trondhj.
12.3
18.7
0.96
40.7
306
Hbl-ite
1.60
16.2
0.24
68.3
289
trondhj.
1.26
16.4
0.21
69.1
289
trondhj.
1.05
19.6
0.25
66.4
289
1.22
18.6
0.26
62.7
289
Pl cumul. Pl cumul.
11.1
17.5
0.67
52.2
289
tonal.
1.80
17.1
0.26
69.1
289
trondhj.
-97.782733 -97.78345 -97.805516 -97.812466 -97.82655 -97.838383 -97.878516 -97.878566
18.2605
TT-54
0.0
0.0
11.2
0.00
0.1
0.10
306
hbl gabbro
-97.7994
18.278833
Lat
Name
0.8
U
1.5
0.5
0.3
0.0
12.1
10.5
Th
0.2
0.14
0.04
Lu
tonal.
Hf
289
Age (Ma)
TT-13B
-97.88385 -97.88385 -97.890866 -97.899783
289
trondhj.
Lithology
TT-13A
18.214033 18.214033 18.208433
289
-97.8837
Qz granitoid
-97.85943
Lon
TT-12
18.214116
TT-11
18.228366
Lat
Name
tablas geoquímica
120
5
4
35
14
77
38
163
2
44
18
31
22
43
2
2
Cu
36
3
6
Ni
11
313
114
52
1
Co
66
103
Y
12
Cr
69.8
Zr
21
V (ppm)
60.2
100.0
515
46.9
Mg#
100.0
3.55
0.01
569
100.0
Total
3.32
0.03
18
2.64
LOI
1.30
348
0.05
P2 O5
1.27
1.96
Sr
0.97
K2 O
1.34
9.05
Rb
5.41
Na2 O
14.48
9.79
0.165
7
1.61
CaO
2.37
0.057
306
13
0.59
MgO
306
Ga
0.029
MnO
-97.78115
Zn
289
Age (Ma)
TT-26B
18.2597
-97.78115
trondhj.
-97.788783
Lithology
Lon
TT-26A
18.2597
TT-25
18.266666
Lat
Name
TT-28
TT-49
18.260116 18.229316
TT-50
TT-51
18.232683 18.235433
TT-52
18.2292
TT-53
18.2203
TT-54
18.220783
11
4
168
32
15
8
2
3
0
16
10
60.4
100.0
0.38
0.05
1.93
5.83
0.88
0.24
0.018
306
trondhj.
11
10
270
22
15
63
97
62
47
64
434
61.4
100.0
2.87
0.02
0.68
1.35
11.3
10.95
0.180
306
Hbl-ite
72
5
591
8
19
33
3
4
4
8
29
26.9
100.0
3.27
0.07
0.40
5.01
4.64
0.33
0.032
289
trondhj.
58
2
539
10
16
19
2
6
2
13
28
22.9
100.0
2.98
0.06
0.47
5.83
3.54
0.21
0.029
289
trondhj.
70
5
198
7
15
4
1
4
1
6
27
26.3
100.0
0.49
0.07
0.25
11.28
0.48
0.21
0.022
289
85
2
213
6
13
22
2
7
1
13
32
60.8
100.0
3.29
0.08
0.22
10.33
2.14
1.06
0.044
289
Pl cumul. Pl cumul.
44
38
229
11
18
98
50
13
24
5
270
43.6
100.0
1.27
0.08
0.53
3.77
7.93
4.79
0.216
289
tonal.
78
5
874
15
19
49
4
6
3
10
30
42.3
100.0
1.24
0.08
0.77
5.60
3.29
0.74
0.039
289
trondhj.
-97.782733 -97.78345 -97.805516 -97.812466 -97.82655 -97.838383 -97.878516 -97.878566
18.2605
TT-27
tablas geoquímica
121
0.8
2.0
0.3
1.5
0.4
0.3
0.8
0.13
2.7
0.3
1.2
0.4
0.3
0.4
0.05
Ce
Pr
Nd
Sm
Eu
Gd
Tb
4.9
Pb
0.0
0.2
Lu
0.00
0.08
0.04
Yb
0.1
0.5
0.3
Tm
0.00
0.08
0.06
Er
Ta
0.6
0.4
Ho
Hf
0.9
0.19
0.4
0.11
Dy
3.3
15.5
10.3
0.2
936
0.2
812
1.3
Cs
306
306
7.2
3.8
Ba
-97.78115
La
0.0
662
Nb
289
Age (Ma)
TT-26B
18.2597
-97.78115
trondhj.
-97.788783
Lithology
Lon
TT-26A
18.2597
TT-25
18.266666
Lat
Name
TT-28
TT-49
18.260116 18.229316
TT-50
TT-51
18.232683 18.235433
TT-52
18.2292
TT-53
18.2203
TT-54
18.220783
13.1
0.01
0.5
0.08
0.5
0.06
0.5
0.15
0.7
0.07
0.5
0.1
0.4
1.1
0.3
2.5
1.0
1.5
792
0.4
306
trondhj.
6.6
0.00
0.6
0.13
1.0
0.18
1.1
0.42
2.2
0.33
2.1
0.7
1.6
3.8
0.6
3.2
0.9
0.0
562
0.4
306
Hbl-ite
0.0
10.1
1.5
395
0.0
289
trondhj.
10.9
2.6
3.1
348
0.0
289
trondhj.
6.7
12.3
3.5
86
0.0
289
1.5
0.01
2.4
0.05
0.4
0.04
0.3
0.12
0.4
0.05
0.6
0.3
0.4
2.0
0.5
4.1
1.9
3.6
70
0.4
289
Pl cumul. Pl cumul.
6.0
9.5
6.9
657
3.9
289
tonal.
0.0
11.1
4.6
561
0.0
289
trondhj.
-97.782733 -97.78345 -97.805516 -97.812466 -97.82655 -97.838383 -97.878516 -97.878566
18.2605
TT-27
tablas geoquímica
122
-97.78115
TT-27
TT-28
TT-49
18.260116 18.229316
TT-50
TT-51
18.232683 18.235433
TT-52
18.2292
TT-53
18.2203
2.3
0.4
306
trondhj.
2.0
0.1
306
Hbl-ite
0.0
289
trondhj.
0.7
289
trondhj.
1.3
289
3.0
0.3
289
Pl cumul. Pl cumul.
0.0
289
trondhj.
TT-60
5.88
0.081
3.10
7.38
5.53
Fe2 O3
MgO
CaO
Na2 O
22.7
Al2 O3
MnO
51.9
0.77
SiO2 (wt %)
289
Age (Ma)
TiO2
tonal.
Lithology
5.69
3.33
1.36
0.043
2.43
17.5
0.35
66.8
289
trondhj.
5.39
3.77
0.72
0.037
1.84
17.5
0.26
69.1
289
trondhj.
2.76
6.23
4.20
0.185
9.68
17.2
0.71
54.3
289
tonal.
-97.8749
TT-72
18.2581
TT-73
18.2502
TT-74
18.2394
6.47
7.25
3.80
0.074
6.69
20.6
0.86
49.8
289
tonal.
3.44
7.85
5.22
0.131
10.5
17.5
0.79
48.0
306
hbl gabbro
7.83
0.24
0.22
0.017
0.56
16.3
0.20
72.9
289
trondhj.
5.47
3.02
0.21
0.029
1.53
16.5
0.23
69.9
289
trondhj.
-97.88695 -97.851633 -97.849716 -97.85045
-97.88085 -97.88055 -97.88045
TT-59
Lon
TT-57
18.215866 18.216316 18.208316 18.207433 18.200566
TT-56
6.46
2.53
0.95
0.033
1.86
16.5
0.26
68.6
289
TT-77
5.47
2.96
0.97
0.041
1.86
17.4
0.27
68.6
289
trondhj.
-97.868
18.223166
TT-78
5.45
8.29
2.17
0.075
5.37
23.4
0.67
52.5
289
tonal.
-97.868066
18.21865
quartz diorite
-97.863433
18.22865
TT-76B
-97.8883
18.22095
TT-79
0.1
289
tonal.
6.50
1.85
0.74
0.034
1.56
17.0
0.24
69.8
289
quartz diorite
TT-55
TT-54
18.220783
-97.782733 -97.78345 -97.805516 -97.812466 -97.82655 -97.838383 -97.878516 -97.878566
18.2605
Lat
Name
U
0.0
0.1
0.0
4.2
Th
0.0
306
306
289
Age (Ma)
TT-26B
18.2597
-97.78115
trondhj.
-97.788783
Lithology
Lon
TT-26A
18.2597
TT-25
18.266666
Lat
Name
tablas geoquímica
123
TT-57
TT-59
TT-60
5
4
16
11
16
66
25
8
1122
Cr
Co
Ni
Cu
Zn
Ga
Rb
Sr
1.3
Cs
La
0.0
205
Nb
Ba
8
116
V (ppm)
71
48.4
Mg#
Y
100.0
Total
Zr
701
1.81
LOI
0.50
3.1
322
0.0
67
10
21
42
1
7
6
11
50
49.9
100.0
1.86
0.11
0.57
0.30
K2 O
P2 O5
289
289
Age (Ma)
trondhj.
tonal.
Lithology
1.2
422
0.0
73
4
732
7
19
37
2
4
4
10
30
41.1
100.0
0.79
0.08
0.50
289
trondhj.
4.0
521
3.9
37
21
368
19
16
97
51
11
28
0
244
43.6
100.0
3.99
0.14
0.58
289
tonal.
-97.8749
TT-72
18.2581
TT-73
18.2502
TT-74
18.2394
0.0
42
1.2
27
9
628
2
17
83
3
19
29
14
116
50.3
100.0
4.02
0.33
0.12
289
tonal.
4.5
3.7
0.0
205
2.1
1042
1.5
6
49
14
44
195
13
16
5
0
5
2
15
22
41.2
100.0
1.20
0.05
0.48
289
trondhj.
335
34
13
111
59
21
30
38
257
47.0
97.0
3.07
0.10
0.42
306
hbl gabbro
3.0
1.9
467
0.4
64
2
558
12
17
23
1
6
4
9
30
19.6
100.0
2.48
0.06
0.58
289
trondhj.
-97.88695 -97.851633 -97.849716 -97.85045
-97.88085 -97.88055 -97.88045
TT-56
Lon
TT-55
18.215866 18.216316 18.208316 18.207433 18.200566
Lat
Name
2.2
408
0.0
72
2
604
13
18
42
3
5
4
12
30
47.6
100.0
2.20
0.08
0.53
289
TT-77
5.0
507
0.0
71
4
662
18
21
46
4
5
6
11
33
48.2
100.0
1.51
0.09
0.84
289
trondhj.
-97.868
18.223166
TT-78
3.7
4.9
119
1.4
84
6
993
5
27
61
3
10
9
5
96
41.9
100.0
1.55
0.26
0.28
289
tonal.
-97.868066
18.21865
quartz diorite
-97.863433
18.22865
TT-76B
TT-79
-97.8883
18.22095
0.0
463
0.0
68
3
642
24
19
38
3
5
5
10
28
45.8
100.0
1.36
0.07
0.93
289
quartz diorite
tablas geoquímica
124
TT-57
TT-59
TT-60
3.2
0.0
1.7
6.1
0.0
0.0
0.0
0.0
0.0
0.5
U
1.9
7.4
Pb
1.5
0.01
0.07
Ta
Th
1.8
1.0
Hf
0.0
0.5
0.4
0.2
0.05
1.5
0.26
Yb
Tm
Lu
0.2
0.04
1.6
0.26
Er
0.4
0.08
2.3
0.54
Ho
Tb
Dy
0.5
0.07
2.1
0.38
Gd
0.0
0.2
0.6
Eu
0.0
0.7
6.5
3.4
7.3
9.9
289
trondhj.
1.5
6.9
289
306
trondhj.
6.0
13.0
289
hbl gabbro
Sm
3.5
289
tonal.
-97.88695 -97.851633 -97.849716 -97.85045
Nd
18.8
289
tonal.
-97.8749
TT-74
18.2394
0.8
11.0
Ce
289
trondhj.
TT-73
18.2502
1.3
289
Age (Ma)
trondhj.
TT-72
18.2581
Pr
tonal.
Lithology
-97.88085 -97.88055 -97.88045
TT-56
Lon
TT-55
18.215866 18.216316 18.208316 18.207433 18.200566
Lat
Name
0.2
13.5
4.9
289
quartz diorite
-97.863433
18.22865
TT-76B
0.0
0.0
5.0
289
trondhj.
-97.868
18.223166
TT-77
0.0
0.1
0.0
0.02
1.9
0.08
0.5
0.09
0.6
0.24
1.2
0.20
1.9
0.9
1.8
8.3
1.4
9.0
289
tonal.
-97.868066
18.21865
TT-78
TT-79
-97.8883
18.22095
0.0
0.6
4.2
289
quartz diorite
tablas geoquímica
125
TT-6
3.20
0.69
0.05
3.73
100.0
43.5
106
21
Na2 O
K2 O
P2 O5
LOI
Total
Mg#
V (ppm)
Cr
9
54
14
30
Cu
Zn
Ga
Rb
8
3.43
CaO
12
1.61
MgO
Ni
0.064
MnO
Co
11.7
3.73
Al2 O3
0.39
Fe2 O3
71.5
SiO2 (wt %)
metaps.
TiO2
Lithology
24
11
48
10
11
8
19
115
40.5
100.0
4.82
0.06
0.55
3.57
4.68
1.59
0.094
4.16
11.3
0.40
68.8
metaps.
65
19
102
31
26
17
75
161
40.9
100.0
3.89
0.14
1.41
2.79
1.19
2.56
0.066
6.58
16.6
0.60
64.1
metapel.
18.19955
TT-7A
47
20
121
36
38
17
80
158
37.9
100.0
3.33
0.18
1.00
3.83
0.84
2.41
0.070
7.05
16.4
0.68
64.3
metapel.
18.207516
TT-7B
52
16
85
2
27
15
53
135
40.3
100.0
3.50
0.13
1.03
3.74
3.19
2.06
0.060
5.43
15.1
0.66
65.2
metaps.
18.207516
33
15
69
2
10
9
13
94
45.3
100.0
3.58
0.14
0.77
4.48
2.73
2.00
0.056
4.30
14.7
0.50
66.8
metaps.
18.212
TT-8A
TT-8B
66
17
102
24
28
16
65
108
41.7
100.0
6.12
0.13
1.43
2.62
4.83
1.85
0.059
4.61
13.3
0.54
64.5
metaps.
18.212
TT-32
32
12
62
13
17
7
34
111
39.8
100.0
4.48
0.10
0.67
4.85
4.23
1.34
0.080
3.61
13.1
0.51
67.1
metaps.
18.256033
TT-33
81
18
130
33
27
16
68
158
43.3
100.0
5.29
0.16
1.71
2.73
3.60
2.46
0.072
5.74
15.7
0.64
61.9
metaps.
18.2558
TT-34A
117
27
126
21
207
32
368
185
56.9
100.0
5.07
0.17
3.04
1.30
0.76
5.7
0.097
7.69
18.3
0.83
57.0
metapel.
18.242216
TT-34B
TT-35
206
29
134
67
48
22
101
181
32.2
100.0
4.45
0.20
4.70
0.51
0.34
2.07
0.106
7.75
20.3
0.81
58.8
metapel.
18.244316
12
19
78
52
40
33
109
180
48.9
100.0
5.17
0.03
0.42
3.79
5.67
4.87
0.134
9.06
16.9
0.52
53.5
metapel.
18.242216
-97.816666 -97.816666 -97.816866 -97.821616 -97.821616 -97.83385 -97.83385 -97.777466 -97.7779 -97.788966 -97.788966 -97.787583
TT-5B
18.200116
Lon
TT-5A
18.200116
Lat
Name
Tabla 13: Chemical results for the Tecomate Formation. Acatlán Complex, Puebla/Oaxaca, Mexico (part 1/4.)
tablas geoquímica
126
TT-6
20.3
41.1
5.4
22.8
5.4
1.2
5.4
0.86
5.8
1.24
3.4
0.50
13.3
26.7
3.4
13.3
3.2
0.7
3.3
0.51
3.5
0.77
2.2
0.38
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
3.2
0.51
3.9
2.4
0.38
3.3
Lu
Hf
1.1
Yb
26.3
2.2
5.4
Cs
9.7
467
1.7
186
5.3
179
234
98
125
Zr
30
220
Nb
25
20
metapel.
Ba
171
159
metaps.
Y
metaps.
Sr
Lithology
18.19955
TT-7A
42.8
5.0
413
9.1
160
33
171
metapel.
18.207516
TT-7B
6.8
0.43
2.7
0.44
2.9
1.01
4.9
0.79
4.9
1.1
4.7
24.0
6.2
45.8
22.9
3.6
582
9.4
300
24
721
metaps.
18.207516
31.1
1.9
335
2.4
137
19
294
metaps.
18.212
TT-8A
TT-8B
50.3
7.5
601
7.3
216
28
239
metaps.
18.212
TT-32
31.3
0.0
328
0.4
156
18
337
metaps.
18.256033
TT-33
52.4
6.0
417
5.9
157
29
233
metaps.
18.2558
TT-34A
96.7
6.3
766
15.6
224
38
91
metapel.
18.242216
TT-34B
TT-35
63.9
8.0
867
16.7
225
36
122
metapel.
18.244316
4.8
4.9
499
0.0
44
29
307
metapel.
18.242216
-97.816666 -97.816666 -97.816866 -97.821616 -97.821616 -97.83385 -97.83385 -97.777466 -97.7779 -97.788966 -97.788966 -97.787583
TT-5B
18.200116
Lon
TT-5A
18.200116
Lat
Name
tablas geoquímica
127
TT-6
TT-7A
2.2
U
2.2
2.4
6.8
16.9
0.37
metapel.
4.1
22.9
metapel.
5.20
0.082
2.49
2.56
3.81
MgO
CaO
Na2 O
14.5
Al2 O3
MnO
0.51
TiO2
Fe2 O3
66.4
SiO2 (wt %)
4.57
3.25
2.14
0.074
4.52
13.4
0.47
66.9
1.67
1.83
3.36
0.062
7.24
17.6
0.76
58.7
metapel.
-97.7861
TT-7B
0.6
6.6
8.1
0.36
metaps.
18.207516
0.0
8.5
metaps.
18.212
TT-8A
TT-38B
18.247016
TT-8B
0.0
10.7
metaps.
18.212
TT-39
6.10
2.08
1.73
0.072
4.59
15.0
0.45
67.9
metaps.
3.88
5.51
3.77
0.120
7.03
14.3
0.73
59.3
metapel.
TT-40B
4.47
2.29
1.19
0.066
3.02
15.1
0.38
68.0
metaps.
2.89
0.65
1.81
0.056
5.11
15.8
0.66
67.3
metapel.
-97.7841
18.247966 18.248516
-97.785833 -97.785833 -97.785483
metaps.
Lithology
-97.7861
TT-38A
metaps.
TT-37B
-97.787433
TT-37A
Lon
TT-36
18.244033 18.245583 18.245583 18.247016
Lat
Name
3.3
Th
7.0
metaps.
18.207516
TT-32
2.4
11.1
metaps.
18.256033
TT-33
4.5
18.6
metaps.
18.2558
TT-34A
1.4
17.8
metapel.
18.242216
TT-34B
2.5
5.4
metapel.
18.242216
TT-35
TT-43
18.1962
TT-61A
TT-61B
18.1962
TT-62
18.196783
1.94
4.17
2.71
0.079
5.77
14.5
0.61
61.8
metapel.
0.14
0.08
4.76
0.018
1.30
14.2
0.35
72.1
metaps.
0.11
0.15
5.74
0.023
1.97
14.0
0.37
70.6
metaps.
TT-63A
2.06
2.48
3.44
0.182
11.3
16.4
1.70
56.1
meta-ark.
-97.8942
18.19365
4.35
0.54
2.79
0.016
3.31
13.4
0.54
71.2
metaps.
-97.780466 -97.894616 -97.894616 -97.893683
18.2538
2.5
13.2
metapel.
18.244316
0.19
15.50
Pb
metaps.
Ta
Lithology
18.19955
-97.816666 -97.816666 -97.816866 -97.821616 -97.821616 -97.83385 -97.83385 -97.777466 -97.7779 -97.788966 -97.788966 -97.787583
TT-5B
18.200116
Lon
TT-5A
18.200116
Lat
Name
tablas geoquímica
128
40.7
79.3
259
25
119
0.9
248
46.0
129
46
13
19
20
79
15
37
291
25
143
5.9
364
5.7
13.9
28.8
Mg#
V (ppm)
Cr
Co
Ni
Cu
Zn
Ga
Rb
Sr
Y
Zr
Nb
Ba
Cs
La
Ce
22.7
3.8
29
14
67
19
17
13
49
115
45.8
100.0
66.6
5.4
915
11.7
178
27
145
113
23
143
38
39
17
97
180
45.3
100.0
29.1
0.0
243
2.8
126
22
309
8
16
52
10
8
9
21
38
40.2
100.0
1.46
37.7
0.5
321
6.7
171
29
411
14
15
62
20
91
24
171
74
48.9
100.0
4.52
4.6
951
13.5
175
12
253
78
18
59
11
10
4
14
58
41.2
100.0
2.50
0.16
2.85
100.0
5.07
0.27
Total
3.89
0.19
3.44
0.21
0.6
metaps.
LOI
0.10
0.46
metapel.
0.11
metaps.
-97.785833 -97.785833 -97.785483
0.95
3.45
TT-39
TT-40B
81.2
6.3
752
15.5
205
36
173
102
22
98
15
33
14
70
102
38.7
100.0
2.71
0.17
2.92
metapel.
-97.7841
18.247966 18.248516
P2 O5
0.69
TT-38B
18.247016
K2 O
metapel.
-97.7861
metaps.
Lithology
-97.7861
TT-38A
metaps.
TT-37B
-97.787433
TT-37A
Lon
TT-36
18.244033 18.245583 18.245583 18.247016
Lat
Name
18.1962
TT-61A
TT-61B
18.1962
TT-62
18.196783
43.0
2.0
752
7.2
166
31
200
84
18
134
33
34
12
87
150
45.6
100.0
5.93
0.17
2.32
metapel.
74.6
39.6
8.7
600
11.9
291
33
11
69
15
3
1
7
4
5
15
86.7
100.0
3.40
0.05
3.60
metaps.
66.7
0.0
1800
11.7
324
38
11
78
14
5
13
9
12
10
40
83.8
100.0
3.63
0.09
3.36
metaps.
TT-63A
47.7
2.8
528
10.2
121
34
135
77
21
109
28
26
16
37
198
35.2
100.0
4.83
0.30
1.27
meta-ark.
-97.8942
18.19365
52.6
0.5
486
6.9
205
35
96
27
14
7
8
13
14
3
51
60.0
100.0
2.54
0.12
1.25
metaps.
-97.780466 -97.894616 -97.894616 -97.893683
18.2538
TT-43
tablas geoquímica
129
17.3
3.1
TT-40B
-97.7841
3.6
0.0
3.0
4.8
3.4
Th
U
4.5
15.1
Pb
7.7
15.2
24.4
4.1
0.47
3.4
0.21
Ta
Lu
Hf
1.2
0.19
3.3
0.46
Yb
0.6
4.8
4.0
1.3
0.17
3.1
0.46
Er
1.28
2.6
0.47
4.6
0.96
Dy
Ho
6.5
4.2
6.6
6.4
0.51
7.6
0.64
4.0
0.57
6.1
0.95
3.5
0.49
1.4
7.1
39.3
8.9
metaps.
4.1
19.7
metapel.
0.70
Tm
TT-61B
18.1962
TT-62
18.196783
3.1
2.2
metaps.
0.7
7.7
metaps.
-97.780466 -97.894616 -97.894616 -97.893683
18.1962
TT-61A
Tb
15.0
metapel.
TT-43
18.2538
Gd
5.1
1.1
4.0
0.9
Sm
Eu
8.9
metaps.
32.7
metapel.
3.8
metaps.
-97.785833 -97.785833 -97.785483
14.8
89.4
TT-39
18.247966 18.248516
Pr
10.6
TT-38B
18.247016
Nd
metapel.
-97.7861
metaps.
Lithology
-97.7861
TT-38A
metaps.
TT-37B
-97.787433
TT-37A
Lon
TT-36
18.244033 18.245583 18.245583 18.247016
Lat
Name
2.3
14.5
meta-ark.
-97.8942
18.19365
TT-63A
tablas geoquímica
130
7.30
0.109
2.15
0.36
0.84
4.11
0.18
4.53
100.0
34.4
138
100
18
41
24
114
27
188
MgO
CaO
Na2 O
K2 O
P2 O5
LOI
Total
Mg#
V (ppm)
Cr
Co
Ni
Cu
Zn
Ga
Rb
19.3
Al2 O3
MnO
0.88
TiO2
Fe2 O3
60.3
SiO2 (wt %)
-97.8942 -97.899566 -97.899333 -97.899166 -97.898883
42
13
44
10
13
7
20
65
39.5
100.0
2.33
0.09
1.12
3.47
1.89
1.31
0.085
3.58
12.8
0.42
72.9
35
12
41
10
10
5
18
57
47.7
100.0
2.75
0.08
1.01
4.06
1.43
1.74
0.102
3.40
12.9
0.39
72.2
meta-ark.
47
13
67
11
14
9
30
108
37.3
100.0
3.06
0.07
1.04
3.78
2.21
1.52
0.081
4.55
13.1
0.62
70.0
meta-ark.
TT-68
TT-69
TT-70
-97.89785
TT-83A
-97.816666
18.200116
TT-84
TT-85
18.1894
-97.893266 -97.89225
18.193816
41
14
48
9
15
4
26
74
42.0
100.0
2.00
0.10
1.01
4.23
1.13
1.58
0.090
3.89
13.5
0.44
72.1
48
16
53
11
13
8
23
106
39.7
100.0
2.57
0.10
1.19
3.50
1.90
1.88
0.103
5.09
14.2
0.50
68.9
96
19
136
26
43
17
92
142
44.0
100.0
6.38
0.16
2.61
1.57
4.73
2.72
0.077
6.16
14.4
0.64
60.5
5
12
19
11
7
3
13
38
44.7
100.0
3.99
0.03
0.25
5.12
4.52
0.72
0.065
1.59
10.7
0.22
72.8
129
26
75
32
37
16
86
130
38.6
100.0
3.28
0.18
4.31
0.86
0.52
2.35
0.078
6.66
17.9
0.72
63.1
43
13
64
9
17
11
41
113
43.6
100.0
3.55
0.06
1.03
3.27
2.18
1.94
0.091
4.48
12.6
0.47
70.3
meta-ark. meta-ark. metapel. meta-congl. meta-ark. meta-ark.
-97.8983
18.190683 18.191466 18.19185
metapel. meta-ark.
TT-67
18.1902
Lithology
TT-66
18.1901
Lon
TT-65
Lat
18.18985
TT-63B
18.19365
Name
TT-87
5
8
21
33
6
5
13
34
34.6
100.0
2.12
0.07
0.26
5.76
2.56
0.72
0.065
2.43
11.7
0.34
74.0
meta-congl.
-97.887
18.1779
54
18
107
33
27
15
74
153
45.9
100.0
4.02
0.13
1.30
3.29
2.29
2.89
0.083
6.06
15.2
0.59
64.1
metaps.
-97.8879
18.177616
TT-86
tablas geoquímica
131
924
7.7
Ba
Cs
5.5
2.3
426
0.3
351
3.3
114
32
143
3.5
308
290
8.7
366
2.6
0.40
6.6
Yb
Lu
Hf
2.1
0.32
0.74
Ho
Tm
3.5
Dy
Er
3.4
0.50
Tb
0.9
Gd
3.6
Eu
4.3
16.8
35.5
Nd
29.6
Sm
Pr
101.0
29.8
1.6
90
17
0.0
TT-69
TT-70
-97.8983
-97.89785
TT-83A
-97.816666
18.200116
TT-84
TT-85
18.1894
-97.893266 -97.89225
18.193816
31.2
5.5
416
3.0
127
33
120
64.1
6.6
739
9.1
159
34
216
46.3
5.9
74
3.4
159
67
159
82.2
2.6
689
16.4
187
38
64
28.2
3.6
420
2.7
170
23
139
134
35.3
20.3
Nb
132
29
98
17.2
206
Zr
32
95
meta-ark.
Ce
47
Y
meta-ark.
La
47
Sr
-97.8942 -97.899566 -97.899333 -97.899166 -97.898883
TT-68
18.190683 18.191466 18.19185
metapel. meta-ark.
TT-67
18.1902
Lithology
TT-66
18.1901
Lon
TT-65
Lat
18.18985
TT-63B
18.19365
Name
TT-87
22.5
0.6
213
2.9
195
40
121
meta-congl.
-97.887
18.1779
36.6
2.9
469
5.4
163
30
207
metaps.
-97.8879
18.177616
TT-86
tablas geoquímica
132
-97.8942 -97.899566 -97.899333 -97.899166 -97.898883
3.3
0.0
2.3
U
8.6
4.8
Th
12.2
0.33
12.9
13.1
23.9
Pb
meta-ark.
Ta
meta-ark.
TT-68
TT-69
TT-70
-97.89785
TT-83A
-97.816666
18.200116
TT-84
TT-85
18.1894
-97.893266 -97.89225
18.193816
4.0
6.5
3.7
12.9
0.0
14.3
6.1
42.0
3.7
10.8
3.2
10.5
-97.8983
18.190683 18.191466 18.19185
metapel. meta-ark.
TT-67
18.1902
Lithology
TT-66
18.1901
Lon
TT-65
Lat
18.18985
TT-63B
18.19365
Name
4.4
15.1
metaps.
-97.8879
18.177616
TT-86
3.1
18.6
meta-congl.
-97.887
18.1779
TT-87
tablas geoquímica
133
tablas geoquímica
Tabla 16: Chemical results for the Tecomate Formation. Acatlán
Complex, Puebla/Oaxaca, Mexico. (part 4/4)
Name
TT-88
TT-89
TT-90
TT-91
TT-486B
Lat
18.178133
18.1788
18.179283
18.176533
18.28409
Lon
-97.886583
-97.887366
-97.8867
-97.88415
-97.91114
Lithology
meta-ark.
meta-ark.
meta-ark.
meta-ark.
metaps.
SiO2 (wt %)
65.7
64.2
71.2
71.1
75.16
TiO2
0.57
0.61
0.43
0.46
0.853
Al2 O3
13.3
16.1
13.4
13.3
11.31
Fe2 O3
4.30
6.12
3.72
3.99
3.92
MnO
0.100
0.083
0.067
0.068
0.053
MgO
1.82
2.99
1.53
1.64
0.97
CaO
4.02
1.80
2.08
1.96
1.07
Na2 O
4.30
3.14
4.71
4.13
2.18
K2 O
1.08
1.69
0.70
0.88
2.16
P2 O5
0.14
0.15
0.08
0.10
0.124
LOI
4.70
3.16
2.04
2.44
2.26
Total
100.0
100.0
100.0
100.0
100.06
Mg#
43.0
46.5
42.3
42.3
V (ppm)
113
144
84
83
77.4
Cr
42
86
25
43
49.3
Co
13
14
10
13
10.5
Ni
24
27
12
21
19.4
Cu
22
29
20
11
35.9
Zn
74
112
52
60
47.1
Ga
15
19
14
15
16.6
Rb
51
70
23
39
77.9
Sr
277
216
237
217
127.2
Y
19
28
24
19
40.8
Zr
146
162
105
130
459.3
Nb
4.0
7.7
2.9
4.2
18.3
Ba
614
633
363
309
786
Cs
5.6
1.6
3.0
3.1
4.3
36.8
42.3
24.7
39.1
66.1
16.5
14.3
99.6
67.7
La
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
Hf
Ta
Pb
Th
U
8
14.8
3.0
2.5
2.4
3.3
1.8
134
TT-561
16.9
1.00
0.016
0.3
1.69
5.90
2.75
0.05
1.29
100.5
37.3
11
0
1
4
6
37
Al2 O3
MnO
MgO
CaO
Na2 O
K2 O
P2 O5
LOI
Total
Mg#
V (ppm)
Cr
Co
Ni
Cu
Zn
0.16
Fe2 O3
70.5
SiO2 (wt %)
granite
TiO2
Lithology
37
3
2
0
0
11
45.0
100.2
1.16
0.04
2.76
5.74
1.28
0.33
0.015
0.80
16.6
0.15
71.3
granite
32
1
4
1
0
13
38.7
100.3
1.15
0.05
2.67
5.72
1.93
0.29
0.02
0.91
16.8
0.16
70.6
granite
8
6
5
2
0
13
23.5
100.6
1.16
0.04
2.11
4.58
0.28
0.15
0.001
0.97
13.7
0.17
77.4
granite
18.195765
TT-562
20
16
4
3
0
14
13.8
100.6
1.05
0.04
5.01
2.95
0.7
0.18
0.040
2.23
12.6
0.33
75.5
granite
18.1957822
TT-563
8
2
4
0
0
11
14.0
100.3
0.98
0.04
5.49
2.86
0.67
0.06
0.026
0.73
12.6
0.42
76.4
granite
18.1954056
TT-564
12
3
3
1
0
16
23.0
100.4
1.44
0.07
4.31
4.15
0.71
0.16
0.034
1.06
15.2
0.23
73.1
granite
18.2019813
TT-565A
74
13
5
3
0
14
31.1
99.1
0.77
0.19
1.53
4.44
7.03
0.83
0.05
3.65
21.2
0.55
58.9
diorite
17.299662
TT-565B
125
6
5
8
0
39
31.1
99.6
1.00
0.46
1.77
3.53
6.46
1.83
0.15
8.02
18.2
0.79
57.4
diorite
17.299662
TT-566
121
8
6
10
4
55
36.0
100.2
1.01
0.56
1.56
3.61
7.06
2.20
0.14
7.76
18.4
0.84
57.0
diorite
17.2997669
TT-568
TT-569
65
35
1
2
0
6
19.4
100.3
0.56
0.10
1.77
4.63
4.18
0.41
0.04
3.37
17.8
0.29
67.1
granodiorite
17.2999334
218
394
42
34
109
203
36.9
100.0
1.05
0.55
1.54
1.96
8.29
5.62
0.21
19.1
11.6
1.54
48.6
gabbro
17.2999866
-97.4503084 -97.449797 -97.4505566 -97.500517 -97.5017058 -97.5009734 -97.5132829 -97.0109535 -97.0109535 -97.0116326 -97.0125795 -97.0113175
TT-560
Lon
TT-559
18.1261932 18.1268127 18.1278242
TT-558
La Carbonera stock
Lat
Name
Cozahuico granite
Tabla 17: Chemical results for the Cozahuico granite as well as La Carbonera stock, Puebla/Oaxaca, Mexico.
tablas geoquímica
135
TT-561
898
5
160
1.7
1467
Sr
Y
Zr
Nb
Ba
TT-562
TT-563
23
116
7.0
402
105
1.5
1603
6.4
1.6
1.4
1.3
0.24
1.6
0.32
0.9
0.12
0.4
0.7
0.10
0.6
0.12
0.4
0.06
Eu
Gd
Tb
Dy
Ho
Er
Tm
18.0
1.1
14.6
5.4
Sm
5.9
Nd
4.4
1.5
1.4
Pr
11.2
10.7
1197
4.3
459
7
115
79
12
granite
Ce
53.8
1004
2.5
354
5
86
77
17
granite
6.7
39.2
116
4
46
17
granite
972
31
19
granite
18.1954056
5.4
20.9
1188
1.8
145
5
767
31
19
granite
18.1957822
La
22.2
32
Cs
19
Rb
granite
Ga
Lithology
18.195765
TT-564
0.07
0.5
0.16
0.8
0.14
0.9
0.5
1.8
10.8
3.0
25.7
14.4
1.2
409
5.9
140
4
184
133
21
granite
18.2019813
TT-565A
0.08
0.69
0.27
1.70
0.30
2.06
1.79
3.61
19.2
4.79
37.4
18.7
0.7
1146
5.9
367
7
1037
25
22
diorite
17.299662
TT-565B
0.22
1.56
0.58
3.23
0.56
3.50
1.66
4.62
22.8
5.33
40.5
19.3
1236
6.9
130
16
703
35
21
diorite
17.299662
TT-566
37.00
49.6
871
9.2
123
28
724
27
21
diorite
17.2997669
TT-568
TT-569
0.05
0.35
0.14
1.04
0.23
1.65
1.31
3.54
21.0
5.32
42.5
21.2
1546
5.9
175
4
703
22
20
granodiorite
17.2999334
0.75
5.84
2.30
13.1
2.27
14.8
2.85
18.1
73.0
14.5
85.1
29.3
1057
15
273
57
250
25
17
gabbro
17.2999866
-97.4503084 -97.449797 -97.4505566 -97.500517 -97.5017058 -97.5009734 -97.5132829 -97.0109535 -97.0109535 -97.0116326 -97.0125795 -97.0113175
TT-560
Lon
TT-559
18.1261932 18.1268127 18.1278242
TT-558
La Carbonera stock
Lat
Name
Cozahuico granite
tablas geoquímica
136
TT-561
TT-562
TT-563
12.5
0.0
0.7
U
0.7
0.5
Th
5.0
0.2
2.7
0.2
10.3
0.0
Pb
3.4
Ta
0.00
10.0
0.21
2.8
0.08
Hf
10.0
granite
0.9
granite
0.14
granite
0.4
granite
0.07
granite
18.1954056
Lu
granite
18.1957822
Yb
Lithology
18.195765
TT-564
1.4
5.3
9.4
0.33
3.7
0.09
0.5
granite
18.2019813
TT-565A
0.00
2.59
0.00
0.22
6.48
0.10
0.70
diorite
17.299662
TT-565B
1.70
2.09
5.50
0.29
2.96
0.24
1.51
diorite
17.299662
TT-566
0.80
0.20
diorite
17.2997669
TT-568
3.60
3.09
9.70
0.39
6.85
0.68
4.64
gabbro
17.2999866
TT-569
2.10
2.16
0.00
0.19
3.94
0.03
0.20
granodiorite
17.2999334
-97.4503084 -97.449797 -97.4505566 -97.500517 -97.5017058 -97.5009734 -97.5132829 -97.0109535 -97.0109535 -97.0116326 -97.0125795 -97.0113175
TT-560
Lon
TT-559
18.1261932 18.1268127 18.1278242
TT-558
La Carbonera stock
Lat
Name
Cozahuico granite
tablas geoquímica
137
TA B L A S A N Á L I S I S D E M I C R O S O N D A
M., Keppie, J.D., Murphy, J.B., y Lee, J.K.W., Arc plutonism in a
transtensional regime: the Late Palaeozoic Totoltepec pluton, Acatlán
Complex, southern Mexico: International Geology Review, en prensa, doi:
10.1080/00206814.2012.693247.
138
D
27.41
0.06
0.00
27.38
Al2 O3
6.29
0.04
0.05
0.01
0.00
100.50 101.20 100.66 100.04
Na2 O
K2 O
SrO
NiO
BaO
Total
0.00
0.00
0.00
0.00
1.33
0.00
1.32
0.00
1.27
0.00
Fe2+
1.38
0.00
0.00
1.43
0.00
1.44
Al
0.00
0.00
Ti
0.01
0.00
0.02
0.10
7.44
7.27
2.67
0.01
0.00
0.00
0.05
7.66
6.70
Number of ions on the basis of 8 oxygen atoms
Si
2.57
2.57
2.62
2.72
2.68
0.00
0.00
0.00
0.10
7.75
6.55
0.00
0.05
25.08
0.00
59.77
P2
99.75
0.00
0.00
0.07
0.05
6.43
8.71
0.00
0.04
25.22
0.00
60.04
P3
99.74
0.02
0.00
0.03
0.05
6.20
9.30
0.05
0.01
9.01
0.03
0.00
CaO
0.00
0.06
0.00
24.33
0.00
61.25
P1
FeO
26.31
0.00
59.06
P2
MgO
0.00
57.66
58.12
P3
TiO2
P1
0.01
0.00
0.02
0.04
6.66
8.42
0.00
0.04
26.42
0.00
58.64
P3
0.01
0.01
0.04
0.03
6.68
8.32
0.00
0.04
26.28
0.00
58.65
P1
0.02
0.00
0.00
0.14
7.95
6.12
0.00
0.04
24.66
0.00
60.61
P1
0.00
0.01
0.00
0.07
7.58
7.14
0.00
0.02
25.11
0.00
60.23
P2
0.00
0.00
0.02
0.08
8.18
6.17
0.00
0.07
24.28
0.00
62.77
P3
0.03
0.01
0.00
0.04
4.93
11.63
0.00
0.07
28.47
0.00
55.65
P1
0.01
0.01
0.01
0.06
5.25
11.03
0.00
0.10
28.32
0.00
56.03
P2
0.00
1.40
0.00
2.60
0.00
1.39
0.00
2.61
0.00
1.38
0.00
2.62
0.00
1.30
0.00
2.71
0.00
1.32
0.00
2.68
0.00
1.50
0.00
2.49
0.00
1.49
0.00
2.50
0.00
1.25
0.00
2.74
100.41 100.25 100.07 99.54 100.17 101.56 100.82 100.83
0.01
0.02
0.04
0.05
6.78
8.45
0.00
0.04
26.67
0.00
58.35
P2
TT-14 TT-14 TT-14 TT-13a TT-13a TT-13a TT-55 TT-55 TT-55 TT-54 TT-54 TT-54 TT-17 TT-17
SiO2
wt. %
Specimen
Sample
Tabla 18: Average plagioclase compositions of rocks from the Totoltepec pluton.
tablas análisis de microsonda
139
4.99
Total
0.3
55.7
0.3
100.0
Ab
Or
Total
100.0
54.5
44.1
45.2
4.98
0.00
0.00
An
mol %
0.00
Ba
0.00
0.00
0.00
Sr
Ni
0.00
0.00
K
0.44
0.53
0.43
0.54
Ca
Na
0.00
0.00
Mg
P3
P1
100.0
0.3
57.0
42.7
4.97
0.00
0.00
0.00
0.00
0.55
0.41
0.00
P2
100.0
0.5
67.8
31.7
4.98
0.00
0.00
0.00
0.01
0.67
0.31
0.00
P1
100.0
0.3
67.2
32.5
4.99
0.00
0.00
0.00
0.00
0.66
0.32
0.00
P3
100.0
0.6
64.5
34.9
4.99
0.00
0.00
0.00
0.01
0.64
0.35
0.00
P2
100.0
0.3
59.0
40.7
4.99
0.00
0.00
0.00
0.00
0.59
0.40
0.00
P2
100.0
0.2
58.7
41.0
4.98
0.00
0.00
0.00
0.00
0.58
0.40
0.00
P3
100.0
0.2
59.1
40.7
4.98
0.00
0.00
0.00
0.00
0.58
0.40
0.00
P1
100.0
0.8
69.6
29.6
4.99
0.00
0.00
0.00
0.01
0.69
0.29
0.00
P1
100.0
0.4
65.5
34.1
4.99
0.00
0.00
0.00
0.00
0.65
0.34
0.00
P2
100.0
0.5
70.2
29.3
4.98
0.00
0.00
0.00
0.00
0.69
0.29
0.00
P3
100.0
0.2
43.3
56.5
4.98
0.00
0.00
0.00
0.00
0.43
0.56
0.00
P1
100.0
0.3
46.1
53.5
4.98
0.00
0.00
0.00
0.00
0.45
0.53
0.00
P2
TT-14 TT-14 TT-14 TT-13a TT-13a TT-13a TT-55 TT-55 TT-55 TT-54 TT-54 TT-54 TT-17 TT-17
Specimen
Sample
Tabla 18: Average plagioclase compositions of rocks from the Totoltepec pluton.
140
16.17
12.05
0.92
10.09
15.24
13.12
0.83
10.98
1.69
0.17
98.05
Al2 O3
FeO
MgO
MnO
CaO
Na2 O
K2 O
Total
96.94
0.18
1.71
10.89
0.73
12.34
15.52
10.60
1.04
43.93
A3
TT-14
1.49
8.00
AlIV
Sum T
0.23
0.10
0.93
2.83
0.10
AlVI
Ti
Fe3+
Mg
Mn
M1–3 sites
6.51
Si
T-sites
0.10
2.63
1.01
0.11
0.27
8.00
1.63
6.37
0.09
2.70
0.94
0.11
0.28
8.00
1.56
6.44
Formula c.f. Holland and Blundy (1994)
96.10
0.21
1.79
10.96
0.79
11.01
0.97
45.01
43.51
A2
TT-14
TiO2
A1
TT-14
SiO2
wt. %
Specimen
Sample
0.19
2.10
0.89
0.08
0.30
8.00
1.69
6.31
99.02
0.74
1.90
11.18
1.50
9.55
19.27
11.44
0.72
42.72
A1
TT-13a
0.15
1.86
0.51
0.08
0.52
8.00
1.60
6.40
96.98
0.73
1.94
11.15
1.20
8.22
19.01
11.90
0.71
42.13
A2
TT-13a
0.18
1.97
0.82
0.07
0.42
8.00
1.70
6.30
99.55
0.75
1.81
11.25
1.41
9.00
19.61
12.18
0.66
42.85
A3
TT-13a
0.09
2.36
0.74
0.07
0.55
8.00
1.57
6.43
97.96
0.20
1.93
10.80
0.74
10.86
16.53
12.30
0.62
43.99
A1
TT-55
0.07
2.16
0.71
0.06
0.67
8.00
1.71
6.29
97.22
0.22
1.99
10.88
0.59
9.78
17.12
13.63
0.50
42.51
A2
TT-55
0.08
2.40
0.73
0.07
0.52
8.00
1.58
6.42
98.67
0.21
1.95
11.12
0.68
11.08
16.46
12.28
0.61
44.15
A3
TT-55
0.15
1.99
0.86
0.06
0.50
8.00
1.83
6.17
98.22
0.73
1.92
11.16
1.18
8.99
18.92
13.28
0.56
41.52
A1
TT-54
0.16
2.10
0.97
0.07
0.42
8.00
1.83
6.17
97.95
0.67
1.94
11.00
1.27
9.47
18.68
12.84
0.60
41.48
A2
TT-54
0.14
2.10
0.86
0.07
0.44
8.00
1.74
6.26
98.43
0.66
1.84
11.18
1.13
9.53
18.61
12.52
0.64
42.33
A3
TT-54
0.06
2.89
0.60
0.16
0.39
8.00
1.66
6.34
97.08
0.25
2.17
11.51
0.52
13.30
12.52
11.92
1.49
43.41
A1
TT-28
0.06
2.70
0.43
0.13
0.52
8.00
1.54
6.46
96.10
0.21
2.04
11.82
0.46
12.52
13.34
12.09
1.23
44.63
A2
TT-28
Tabla 19: Average amphibole compositions of rocks from the Totoltepec pluton.
0.06
2.81
0.57
0.17
0.44
8.00
1.67
6.33
97.68
0.26
2.13
11.51
0.51
13.00
12.83
12.30
1.52
43.61
A3
TT-28
0.13
2.50
0.65
0.15
0.16
8.00
1.24
6.76
99.01
0.72
1.11
11.25
1.05
11.48
17.66
8.10
1.33
46.31
A2
TT-17
0.11
2.56
0.73
0.13
0.18
8.00
1.27
6.73
98.42
0.55
1.13
11.43
0.90
11.78
16.94
8.44
1.18
46.07
A3
TT-17
0.12
2.49
0.61
0.14
0.19
8.00
1.21
6.79
99.56
0.73
1.13
11.44
0.96
11.53
17.53
8.17
1.28
46.78
A1
TT-17
141
0.81
5.00
Fe2+
Sum M1–3
1.70
0.19
2.00
Ca
Na
Sum M4
0.28
0.03
0.32
15.32
1.72
Na
K
Sum A
Sum cation
Al(total)
A-site
0.11
Fe
M4 site
A1
TT-14
Specimen
Sample
1.90
15.34
0.34
0.04
0.31
2.00
0.20
1.72
0.08
5.00
0.89
A2
TT-14
1.83
15.32
0.32
0.03
0.28
2.00
0.21
1.71
0.08
5.00
0.88
A3
TT-14
1.99
15.51
0.51
0.14
0.37
2.00
0.18
1.77
0.05
5.00
1.43
A1
TT-13a
2.13
15.56
0.56
0.14
0.42
2.00
0.15
1.81
0.03
5.00
1.87
A2
TT-13a
2.11
15.48
0.48
0.14
0.34
2.00
0.17
1.77
0.05
5.00
1.54
A3
TT-13a
2.12
15.37
0.37
0.04
0.33
2.00
0.22
1.69
0.09
5.00
1.19
A1
TT-55
2.38
15.41
0.41
0.04
0.37
2.00
0.20
1.72
0.08
5.00
1.33
A2
TT-55
2.10
15.39
0.39
0.04
0.35
2.00
0.20
1.73
0.07
5.00
1.20
A3
TT-55
2.33
15.52
0.52
0.14
0.38
2.00
0.17
1.78
0.05
5.00
1.44
A1
TT-54
2.25
15.50
0.50
0.13
0.37
2.00
0.18
1.75
0.06
5.00
1.29
A2
TT-54
2.18
15.48
0.48
0.12
0.35
2.00
0.17
1.77
0.05
5.00
1.39
A3
TT-54
2.05
15.50
0.50
0.05
0.45
2.00
0.16
1.80
0.04
5.00
0.89
A1
TT-28
2.06
15.47
0.47
0.04
0.43
2.00
0.14
1.83
0.02
5.00
1.16
A2
TT-28
Tabla 19: Average amphibole compositions of rocks from the Totoltepec pluton.
2.11
15.48
0.48
0.05
0.44
2.00
0.16
1.79
0.04
5.00
0.94
A3
TT-28
1.40
15.30
0.30
0.14
0.16
2.00
0.16
1.78
0.06
5.00
1.45
A1
TT-17
1.39
15.29
0.29
0.13
0.16
2.00
0.16
1.76
0.08
5.00
1.42
A2
TT-17
1.45
15.26
0.26
0.10
0.16
2.00
0.16
1.79
0.05
5.00
1.29
A3
TT-17
142
Tabla 20: Mica compositions of rocks from the Totoltepec pluton, Puebla, Mexico.
Sample
Specimen
TT-13a TT-13a TT-14 TT-14 TT-54 TT-54 TT-54 TT-54 TT-28 TT-28
Mc-1
Mc-2
Mc-1
Mc-2
Mc-1
Mc-2
Mc-3
Mc-4
Mc-1
Mc-2
46.58
46.32
42.53
43.10
35.42
33.83
35.44
35.44
42.90
42.38
wt. %
SiO2
TiO2
0.07
0.08
0.03
0.28
0.05
0.01
0.11
0.12
0.00
0.02
Al2 O3
31.44
32.13
32.37
32.34
28.24
28.51
27.94
27.91
34.32
35.18
FeO
3.92
3.83
3.15
2.72
1.80
1.72
1.87
1.89
0.93
0.76
MgO
1.46
1.25
0.81
0.90
1.06
1.05
0.94
0.97
0.12
0.00
MnO
0.01
0.00
0.00
0.01
0.00
0.00
0.00
0.00
0.00
0.00
CaO
0.00
0.02
0.02
0.05
0.00
0.01
0.01
0.03
0.00
0.00
Na2 O
0.86
0.92
1.19
1.45
0.90
0.89
0.96
0.94
0.26
0.23
K2 O
10.41
10.43
10.53
10.12
6.64
7.59
6.57
6.68
12.60
12.66
Cr2 O3
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
NiO
0.00
0.00
0.02
0.01
0.03
0.01
0.01
0.00
0.00
0.01
Total
94.75
94.98
90.66
90.99
74.14
73.60
73.85
73.97
91.13
91.24
Formula calculated on the basis of 11 oxygen atoms
T-site
Si
3.17
3.14
3.04
3.05
3.02
2.93
3.03
3.03
3.03
2.99
AlIV
0.83
0.86
0.96
0.95
0.98
1.07
0.97
0.97
0.97
1.01
Sum T
4.00
4.00
4.00
4.00
4.00
4.00
4.00
4.00
4.00
4.00
AlVI
1.69
1.71
1.76
1.75
1.86
1.85
1.85
1.84
1.89
1.91
Mg
0.15
0.13
0.09
0.10
0.14
0.14
0.12
0.12
0.01
0.00
Fe
0.22
0.22
0.19
0.16
0.13
0.12
0.13
0.13
0.05
0.04
Ti
0.00
0.00
0.00
0.01
0.00
0.00
0.01
0.01
0.00
0.00
Mn
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Ca
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Cr
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Ni
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Sum M
2.06
2.06
2.04
2.03
2.12
2.11
2.11
2.11
1.96
1.96
Na
0.11
0.12
0.17
0.20
0.15
0.15
0.16
0.16
0.04
0.03
K
0.90
0.90
0.96
0.91
0.72
0.84
0.72
0.73
1.14
1.14
Sum A
7.08
7.08
7.16
7.14
7.00
7.10
6.99
7.00
7.13
7.13
M-site
A-site
143
0.192
0.100
0.000
46.911
0.000
0.048
1.194
93.973
0.796
0.014
0.139
2.164
Al2 O3
FeO
MgO
MnO
CaO
Na2 O
0.000
0.280
0.000
0.000
0.030
n.d.
n.d.
n.d.
99.998
Mag
NiO
CuO
SO3
P2 O5
BaO
Ce2 O3
Total
Mineral
Chl
100.001
n.d.
n.d.
0.740
0.593
0.103
0.000
0.450
0.000
0.000
0.129
1.435
16.544
29.787
19.558
0.045
30.617
#3
TT-514
Brt
100.000
n.d.
66.132
0.000
32.648
0.515
0.114
0.000
0.000
0.000
0.065
0.526
0.000
0.000
0.000
n.d.
0.000
#4
TT-514
n.d. – not determined
Mineral abbreviations after Whitney y Evans (2010).
Ap
100.001
n.d.
n.d.
51.874
0.488
0.000
0.115
0.000
K2 O
Cr2 O3
0.000
0.108
1.573
0.000
0.000
#2
TT-514
SiO2
#1
TT-514
TiO2
wt. %
Specimen
Sample
Ce-carbonate
100.000
80.452
n.d.
1.379
0.651
0.000
0.783
0.000
0.000
0.000
15.656
0.000
0.891
0.188
0.000
n.d.
0.000
#5
TT-514
Ilm
100.000
n.d.
n.d.
n.d.
0.303
n.d.
0.613
0.105
0.000
0.000
0.136
0.000
0.000
51.772
0.287
46.784
0.000
Op1#1
TT-14
Ilm
99.998
n.d.
n.d.
n.d.
0.000
n.d.
0.236
0.537
0.000
0.000
0.184
0.000
0.467
55.057
0.000
43.329
0.188
Op1#2
TT-14
Ti-Fe-Silicate
100.000
n.d.
n.d.
n.d.
0.000
n.d.
0.000
0.000
0.324
0.000
13.944
0.000
6.915
27.168
9.227
16.861
25.561
Op2#1
TT-14
Mag
100.000
n.d.
n.d.
n.d.
0.177
n.d.
0.031
0.013
0.000
0.000
0.591
0.000
0.000
46.528
0.000
52.660
0.000
Op2#2
TT-14
n.d.
n.d.
Ti-Mag
100.000
n.d.
Ilm
100.001
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
0.425
0.234
0.085
0.669
0.057
1.978
0.000
46.562
0.035
49.779
0.177
Pl1#2
TT-13a
n.d.
0.151
0.096
0.166
0.013
0.000
0.764
0.000
84.648
0.000
13.911
0.251
Pl1#1
TT-13a
Mag
100.000
n.d.
n.d.
n.d.
n.d.
n.d.
0.000
0.481
0.000
0.006
0.588
0.476
0.000
97.420
0.234
0.214
0.581
Pl1#3
TT-13a
Tabla 21: Energy-dispersive x-ray spectroscopy (EDX) results of selected minerals from Totoltepec pluton rocks.
TT-54
Ilm
100.000
n.d.
n.d.
n.d.
n.d.
n.d.
0.204
0.000
0.000
0.995
0.391
4.304
0.310
43.623
0.248
49.925
0.000
Amp3#1
144
Tabla 21: Energy-dispersive x-ray spectroscopy (EDX) results of selected
minerals from Totoltepec pluton rocks. (cont.)
Sample
TT-17
TT-17
TT-17
TT-28
TT-28
Specimen Amp2#1 Amp2#2 Amp3#1 Amp1#1 Amp3#1
wt. %
SiO2
0.000
3.223
31.016
24.43
0.000
TiO2
0.966
76.356
0.000
43.656
0.000
Al2 O3
0.734
0.136
17.259
1.135
0.171
FeO
96.814
16.289
34.596
0.35
25.213
MgO
0.046
0.000
16.141
0
0.000
MnO
0.149
0.465
0.416
0
0.000
CaO
0.000
2.801
0.078
29.921
0.000
Na2 O
0.335
0.482
0.139
0
0.000
K2 O
0.120
0.000
0.000
0
0.031
Cr2 O3
0.836
0.250
0.356
0.466
0.096
NiO
0.000
0.000
0.000
0
0.000
CuO
n.d.
n.d.
n.d.
0
29.630
SO3
n.d.
n.d.
n.d.
0.042
44.858
P2 O5
n.d.
n.d.
n.d.
n.d.
n.d.
BaO
n.d.
n.d.
n.d.
n.d.
n.d.
Ce2 O3
n.d.
n.d.
n.d.
n.d.
n.d.
100.000
100.002
100.001
100.000
99.999
Mag
Ilm
Chl
Ttn
Ccp
Total
Mineral
n.d. – not determined
Mineral abbreviations after Whitney y Evans (2010).
145
TA B L A S G E O C R O N O L O G Í A
E
40 A R /39 A R
M., Keppie, J.D., Murphy, J.B., y Lee, J.K.W., Arc plutonism in a
transtensional regime: the Late Palaeozoic Totoltepec pluton, Acatlán
Complex, southern Mexico: International Geology Review, en prensa, doi:
10.1080/00206814.2012.693247.
Tabla 22: 40 Ar/39 Ar analysis of muscovite sample TT-57 from the Totoltepec pluton.
Step
Laser
Power
Isotope Volumes∗
40 Ar
2σ
39 Ar
2σ
38 Ar
2σ
37 Ar
2σ
36 Ar
2σ
Ca/K
1
0.5
115.453
0. 411
8.798
0.145 0.260 0.045 0.572 0.769 0.121 0.019 0.119
2
<0.75>
724.844
1.276
61.362
0.364 0.827 0.071 0.849 0.883 0.155 0.020 0.025
3
<1.00> 1717.235 3.381 148.840 0.853 1.923 0.143 0.835 1.480 0.212 0.036 0.010
4
<1.25> 1538.433 2.489 135.730 0.714 1.720 0.133 0.953 1.115 0.104 0.030 0.013
5
<1.50> 1568.868 2.644 137.229 0.853 1.755 0.108 0.941 1.226 0.162 0.033 0.013
6
<1.75> 1326.309 1.736 116.912 0.650 1.494 0.117 0.446 0.767 0.088 0.024 0.007
7
<2.00> 1551.918 3.273 137.506 0.810 1.759 0.104 0.994 1.431 0.087 0.029 0.013
8
<2.25>
614.138
1.157
54.235
0.286 0.680 0.061 0.568 0.585 0.028 0.022 0.019
9
<2.50>
512.826
1.202
45.257
0.348 0.589 0.065 0.276 0.879 0.031 0.017 0.011
10
<2.69>
773.110
1.389
68.506
0.478 0.869 0.060 0.565 0.578 0.051 0.019 0.015
11
<2.86>
824.468
1.242
73.204
0.368 0.941 0.059 0.373 0.885 0.035 0.017 0.009
12
<3.02>
647.662
1.231
57.382
0.355 0.723 0.058 0.584 0.885 0.030 0.019 0.019
13
<7.00> 1349.433 2.196 120.344 0.687 1.573 0.104 1.475 1.034 0.038 0.029 0.022
Note: J-Value = 0,015342 ± 0,000046
∗ Measured volumes are 1 × 1012 cm3 NTP
146
6.31
3.64
1.99
3.05
1.96
1.65
1.34
1.79
1.96
1.23
1.38
0.83
<1.00>
<1.25>
<1.50>
<1.75>
<2.00>
<2.25>
<2.50>
<2.69>
<2.86>
<3.02>
<7.00>
3
4
5
6
7
8
9
10
11
12
13
89.66
99.99
84.74
78.46
72.58
68.70
64.05
52.25
42.22
30.44
18.79
6.02
0.75
9.02
11.10
11.09
11.09
11.03
11.10
11.14
11.07
11.09
11.05
11.08
11.09
11.04
0.12
0.10
0.09
0.12
0.14
0.13
0.09
0.09
0.10
0.09
0.10
0.12
0.67
2σ
283.7
283.5
283.6
282.1
283.7
284.7
283.0
283.5
282.6
283.2
283.4
282.2
233.9
Age (Ma)†
2.9
2.3
2.2
2.7
3.4
3.2
2.2
2.1
2.4
2.2
2.3
2.9
16.3
2σ
2σ
0.088836
0.089421
0.089028
0.088848
0.088485
0.088546
0.088841
0.088383
0.087701
0.088462
0.086901
0.084871
0.076372
39 Ar/40 Ar
0.000577
0.000532
0.000469
0.000642
0.000714
0.000497
0.000558
0.000506
0.000566
0.000488
0.000528
0.000527
0.001296
2σ
0.000
0.000
0.000
0.001
0.000
0.000
0.002
0.001
0.002
0.001
0.004
0.003
0.004
r
steps marked by <); Plateau Age = 283,22 ±
0.000030
0.000022
0.000021
0.000025
0.000033
0.000035
0.000019
0.000018
0.000021
0.000020
0.000021
0.000028
0.000169
39 Ar,
0.000047
0.000028
0.000042
0.000066
0.000061
0.000045
0.000056
0.000066
0.000103
0.000068
0.000123
0.000214
0.001053
36 Ar/40 Ar
† Integrated Age = 282,85 ± 1,10Ma; Isotope Correlation Age = 283,41 ± 3,68Ma (99.2 % of
1,10Ma (99.2 % of 39 Ar, steps marked by >); MSWD = 0.248
31.02
0.5
<0.75>
2
40 Ar/39 ArK
%40 Aratm
Power
%39 Ar
Isotope Correlation Data
Laser
1
Step
Tabla 22: 40 Ar/39 Ar analysis of muscovite sample TT-57 from the Totoltepec pluton. (cont.)
tablas geocronología
40 ar/ 39 ar
147
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