GEODAZE 2015 ABSTRACTS - University of Arizona

Transcription

GEODAZE 2015 ABSTRACTS
TABLE OF CONTENTS
Oral Sessions
Economic Geology
02
Geophysics
15
Climate and Paleoclimate
22
Tectonics and Geochemistry
26
GeoDaze Keynote Speaker
37
Geosciences EarthWeek Plenary Speaker
38
Poster Sessions
Economic Geology
39
Geophysics
40
42
48
Planetary Science
62
Environmental Science
64
1
Oral Sessions
Economic Geology
EOCENE HYDROTHERMAL SYSTEMS AND CONTRASTING
HYDROTHERMAL ALTERATION IN THE BATTLE MOUNTAIN DISTRICT,
NEVADA
Caleb A. King
The Battle Mountain district in north-central Nevada hosts numerous Eocene
intrusive centers that have hydrothermal systems, many with associated Cu/Au
mineralization. Mineralization types include porphyry-type Cu-Au(-Mo), distaldisseminated Au, and Au±Cu skarns. These systems contain high-temperature
quartz veins, potassic and sericitic alteration, and abundant sodic-calcic, calcic,
and potassic-calcic alteration. Most systems, including Copper Canyon, Copper
Basin, and the deeply exposed Elder Creek porphyry system, have
superimposed features. For these systems, crosscutting relationships, combined
with published geochronology and 37 new U-Pb dates, demonstrate that the Au(Cu) systems are Late Eocene (39-42 Ma).
Alteration assemblages in these systems form distinct zones and were defined
by mapping secondary mineral assemblages and by petrographic and electron
microprobe studies. Alteration of siliciclastic and igneous rocks includes:
potassic, sericitic, sodic-calcic, calcic, and potassic-calcic alteration. Two types of
skarn occur in the district. Fortitude-type skarns replace carbonate rocks and
consist of Cpx+Gar+Po with Au+Cu, whereas Copper Basin-type skarns replace
feldspathic, silicic and carbonate rocks and consists of Gar+Hem+Mt with
Au+Cu. The volume and distribution of these assemblages, along with petrologic
considerations, indicates two fluid sources: magmatic fluids generated potassic,
sericitic, and Fortitude-type skarns, and moderately saline, non-magmatic fluids
produced Na-Ca(-K) alteration mineral assemblages and Copper Basin-type
skarns. Those features inferred to be magmatic-hydrothermal are restricted in
their extent and related to particular intrusive phases, whereas the Na-Ca-K
alteration typically extends over many kilometers and is not correlated to any
particular intrusive phase.
Reconnaissance and selected mapping in northeastern Nevada has revealed
that other exposed Eocene plutons contain analogous features. Many of these
plutons exhibit local magmatic-hydrothermal features including potassic alteration
and quartz veins, yet the distinctive Na-Ca-K alteration is remarkably widespread
and heretofore, largely unnoted. Observations within the Battle Mountain district
and regionally indicate that a variety of fluids – magmatic and non-magmatic –
played significant roles in Eocene intrusion-centered hydrothermal systems, and
that the consequences of both fluid types need to be considered in interpreting
Cenozoic metallogeny.
2
THALLIUM DISTRIBUTION IN POTASSIUM SILICATES FROM THE BATTLE
MOUNTAIN REGION, NV
Shelby Rader
Thallium (Tl), like many heavy metals (e.g., As, Hg, Pb), presents both economic
opportunities and environmental challenges. Though thallium often occurs
together with mercury, arsenic, and other similar elements in low-temperature
hydrothermal systems, the specifics of thallium geochemistry are poorly
understood. This is due in part to its dual role as a lithophile and chalcophile
element, and thus its occurrence in both silicates and sulfides. In silicate
environments, the distribution of thallium is analogous to lithophile alkali metals
(K+, Rb+, Cs+) due to similar ionic size and charge. When sulfur activity is high,
however, thallium has been shown to also exhibit chalcophile behavior,
partitioning into sulfide phases in both magmatic and hydrothermal environments.
The control of this behavior is currently poorly understood.
This study uses Tl concentration data collected on a Micromass isoprobe MCICP-MS to investigate the first-order controls on the distribution of Tl between
silicate and sulfide phases, as well as between different K-bearing silicate
minerals (e.g., biotite versus K-feldspar). A collection of samples from the Battle
Mountain region in northeastern Nevada were measured. This area records a
mix of magmatic and non-magmatic (external) hydrothermal fluids responsible for
voluminous alteration.
Analyses of Battle Mountain K-feldspar and biotite display Tl concentrations
ranging from below detection (<0.2 ppm) up to 1.96 ppm. Samples from
unaltered rocks range from <0.2 to 1.36 ppm (n = 11, avg. = 0.50 ppm); samples
from Na-Ca alteration range from <0.2 to 1.82 ppm (n = 9, avg. = 0.45 ppm);
samples from weak K alteration range from <0.2 to 1.56 ppm (n = 12, avg. = 0.53
ppm); and samples from strong K alteration range from <0.2 to 1.96 ppm (n = 23,
avg. = 0.73 ppm). Additional whole rock geochemical data was included for
further comparison.
Preliminary evidence suggests that elevated Tl concentrations coincide with
weak to strong potassic alteration, and biotite samples are more enriched in Tl
than coexisting K-feldspar. This mineral-scale study enhances our overall
understanding of Tl distribution and geochemical behavior within heavily altered
and economically mineralized areas.
3
TIME SCALES OF A GEOTHERMAL SYSTEM FROM ACTINOLITE
FE-MG ZONING
Zack McIntire
Estimating the duration of ore-forming and geothermal systems is a longstanding challenge, despite considerable previous research into this issue.
Though geochronological approaches are useful for determining absolute ages,
their precision is typically inadequate to assess duration of hydrothermal events.
Volume diffusion provides a mechanism to constrain the timescales of
hydrothermal activity because the diffusional relaxation of compositional profiles
can be related to temperature and time.
We determined Fe and Mg profiles in delicately zoned actinolite crystals from the
Punta del Cobre Iron Oxide Copper Gold (IOCG) district, northern Chile.
Petrographic analyses were conducted to determine textures, mineral relations,
and mineral orientation. Backscattered electron (BSE) images helped locate the
most abrupt Fe:Mg zoning in actinolite crystals. Based on these observations, we
used Cameca SX 100 electron microprobe (EMP) to measure mineral
compositions along selected C-axis profiles. Traverse steps were done at 0.5
microns. Although this is comparable to the scale of the activation volume in
EMP analysis, overlapping effects could be accounted for in the subsequent data
analysis.
In the absence of Fe-Mg diffusion data for amphibole, orthopyroxene was used
as a proxy for the modeling of the diffusion times. We infer that diffusion along
the M1-M2 strip (parallel to the C-axis) in orthopyroxene will be similar to that
along the M1-M3 strip in amphibole given that these sites contain the Fe and Mg.
Modeling the diffusion profile allowed for the solving of the diffusion coefficient
multiplied by time (Dt). Deconvolution of Dt was conducted to account for the
excess data due to the manner in which the electron beam penetrates and
excites the sample. Temperature was estimated from fluid inclusion data on other
nearby deposits and modern geothermal analogs.
Temperatures from the fluid inclusions and modern analogs were estimated to be
between 350 to 450°C. Using this temperature range and the orthopyroxene
diffusion equations, the diffusion coefficient (D) was found to range from 8.44E26 to 4.83E-22 cm2/s depending on the temperature and the sample. Using this
information, the duration of hydrothermal activity related to actinolite deposition at
Punta Del Cobre was found to range from 10^4 to 10^7 years. In samples with
multiple generations of actinolite textures, the younger textures were associated
with less diffusion than the older textures.
4
FE OXIDE-RICH MINERALIZATION AND RELATED ALTERATION IN THE
YERINGTON DISTRICT, NEVADA: AN UPDATE
Simone Runyon
The Fe oxide-rich Minnesota and Pumpkin Hollow deposits formed along the
margin of the 169 Ma Yerington batholith. The Minnesota mine is a magnetite
replacement body hosted in a fault slice of early Mesozoic sedimentary and
volcanic rocks. The Pumpkin Hollow replacement-hosted Fe and Cu resources
are contained in several ore bodies hosted by the same rocks as at Minnesota.
Both localities are associated with Ca (-Na) altered quartz monzodiorite. Dilles
and others (2000; SEG Field Guide 32) note that these deposits resemble iron
oxide copper gold (IOCG) deposits and occurrences of Na-Ca alteration
observed across the Yerington batholith. This study uses recent mapping,
petrography, and mineral analyses to document and compare the characteristics
of magnetite-rich systems with magnetite-poor Cu-rich skarn mineralization in the
district.
Mineralization at Minnesota and Pumpkin Hollow contains Na-Ca alteration of
associated igneous units, multiple episodes of brecciation, relatively low Siaddition, and magnetite-dominated carbonate-replacement. In both systems,
magnetite ± actinolite locally replaces carbonate, impure carbonate, and
aluminosilicate host rocks. Crosscutting relationships between igneous rocks and
hydrothermal alteration suggest that the majority of magnetite-dominated
mineralization at both deposits occurred relatively early during emplacement of
the Yerington batholith.
There is a batholith-wide relationship between Na-Ca alteration in igneous units
and associated Fe-oxide mineralization. Shallow Fe-oxide rich (specularite +
chalcopyrite) vein or lode deposits are associated with Na-Ca alteration of
igneous units (e.g., Blue Jay, Northern Lights, and Buckskin mine). Intermediate
Fe-oxide rich deposits consist of magnetite-cemented breccias ± chalcopyrite
associated with voluminous Na-to Ca-alteration (Minnesota mine and Pumpkin
Hollow) or voluminous Na-alteration with magnetite-apatite-chalcopyrite
mineralization (Easter prospect).
Magnetite-rich deposits differ from the garnet-salite rich copper skarn (Casting
Copper, Mason Valley) and quartz-pyrite lode deposits (Bluestone, Ludwig) that
lack abundant magnetite (Einaudi, 2000). These magnetite-poor deposits are
hosted in the same part stratigraphic units, but have higher silicate addition, and
are related to late-stage granite porphyry dikes. Fe oxide-rich systems are
distinct from Fe oxide-poor systems in the Yerington district and are similar to
IOCG systems documented around the world.
5
VEIN-HOSTED AG (±CU, PB, ZN) AND W (±PB, ZN, CU) MINERALIZATION IN
THE CERRO COLORADO AND LAS GUIJAS DISTRICTS, PIMA COUNTY,
ARIZONA
J.D. Mizer
The historic Cerro Colorado and Las Guijas Districts in Pima County, Arizona
were mined for vein-hosted silver, tungsten, and base metals even before
Spanish explorers prospected the area in 1775. Host rocks in the district include
Late Cretaceous andesite flows and breccia, Bisbee Group sedimentary units,
and granitic intrusive rocks. Silver is found in polymetallic sheeted quartz veins
up to one meter wide that strike east-west and cut an earlier group of weakly
mineralized quartz-siderite/ferroan calcite-barite-dolomite veins that strike N40°E.
Electron microprobe analyses document that silver in the districts is contained in
sulfide and sulfosalt minerals such as acanthite, balkanite, and imiterite and to a
lesser degree tetrahedrite, galena, sphalerite, and covellite. Oxide minerals
including chlorargyrite and perroudite are also present. Abundances of these
minerals vary greatly between mineralized localities, displaying the diversity of
mineral distribution across the district. Acid alteration of varying intensity is often
found proximal to these veins, ranging from weak sericitic-replacement of
feldspars to clay-alteration of igneous mafic minerals (pyroxene/amphibole) and
feldspars. Pervasive propylitic alteration is also present in the district, consisting
of chlorite replacing biotite, pyroxene, and hornblende in addition to feldspars
being replaced by epidote or altered to clay. Current mapping indicates no spatial
relationship between veins and propylitic alteration.
Cross-cutting relationships observed between igneous rocks and hydrothermal
alteration provide important timelines that constrain the space-time development
of alteration-mineralization across the districts. This study constrains the timing of
Laramide and early Tertiary magmatic events with new U-Pb ages from zircon,
and documents at least two generations of fault-controlled, Ag-bearing veins. The
findings of this study will improve our understanding of the geologic and
hydrothermal history of the Las Guijas and Cerro Colorado districts.
This case study is expanded to the porphyry copper region of southwestern
North America to include the overall timing of volcanic, magmatic, and
mineralizing events. The ages presented in this study are incorporated into a
growing U-Pb database for Laramide rocks in southwestern North America,
thereby contributing to a more complete understanding of Laramide magmatism
and associated hydrothermal systems.
6
CHUKARU PEKI PROJECT, TIMOK CU-AU DISTRICT, SERBIA
Matthew Wetzel
Chukaru Peki is a recently discovered, concealed, high-grade Cu-Au deposit
within the Timok Cu-Au metallogenic belt, Serbia. The Timok district is located
near the town of Bor, in Eastern Serbia and is one of Europe’s largest and most
productive Cu-Au porphyry copper districts containing over 20Mt Cu and 1000t
Au. The Timok district contains the cretaceous aged Bor, Veliki Krivilj, and
Majdanpek porphyry copper deposits, as well as many other base metal and
lesser significant porphyry systems. Chukaru Peki is a composite system with
upper zone exhibiting high-grade massive sulfide mineralization contained within
a variable envelope of advanced argillic alteration. Upper zone mineralization
and alteration partially overprints the underlying alteration and mineralization
indicative of classic Cu-Au porphyry type mineralization, found in many major
porphyry copper districts around the world. The two styles of mineralization are
thought to be genetically linked, but the extent to which they are linked is still
uncertain. It is likely that the high sulfidation epithermal-massive sulfide
mineralization, formed during the last phase of mineralization related to the
emplacement of the Cu-Au porphyry deposit. Chukaru Peki is concealed by
approximately 400-600m of post-mineral, late Cretaceous clastic rocks, marls,
and Miocene sediments. Chukaru Peki is hosted in a thick sequence of
Cretaceous hornblende andesite, cut by later porphyritic dikes of andesite-diorite
composition. The structural regime is complicated, exhibiting contraction related
faulting and tilting, pull apart basins related to transform faulting, and recent
localized extension related faulting. Initial results, based on the detailed logging
of over 5000m of core, collection of samples over 100 samples and extensive
geochemical sampling of drill core has helped in the identification of different
lithologies, alteration assemblages, geochemical zonation, and identifying major
structures. This information is used to help define alteration assemblages,
mineral distribution, and paragenesis, in an effort to understand the conditions of
formation of the Chukaru Peki deposit.
7
THE DIRTY LIFE AND TIMES OF NORMAL FAULTS: IMPLICATIONS FOR
FAULT MECHANICS FROM CROSSCUTTING RELATIONSHIPS IN HIGHLY
EXTENDED DOMAINS
Carson A. Richardson
Normal faults are observed at a variety of dips with differing evidence provided
by pre-/syn-extensional markers to support the view that they have rotated from
higher angles. Following from Andersonian mechanics, normal faults are
expected to nucleate ~30° from σ1 (~60° initial dip). Normal faults are then
expected to slip and rotate until the fault is ~60° from σ1 (~30° dip) following
Byerlee’s Law at which point the fault is expected to lock up (Ignoring any
influence fluid pressure may have on the fault mechanics involved and assuming
that the fault ceased movement due to locking up.). This study examines
extended domains where the initial dips of faults can be ascertained and seeks to
better constrain at what dips are faults observed to lock and to be cut by a
younger generation of faults.
In the surveyed extended domains, structural reconstructions indicate that
normal faults are found to lock up at significantly higher angles than predicted by
Byerlee’s Law. In the Yerington district, where three major generations of faults
have extended the district ~150%, faults of the active generation cut the second
generation faults when the second generation faults had dips of ~45°, suggesting
that the second generation faults had locked up at 45° from σ1. The second
generation faults had in turn cut the first generation faults when had dips of ~38°
(~52° from σ1).
The controls on the angle of death for normal faults are currently unclear, but
possible factors exerting influences are strain rate, associated magmatism, the
time-span of extension, and the amount of tilting per unit of slip.
8
FAULT-SURFACE RECONSTRUCTION AND EPIDOTE NORMALIZATION AT
SAN MANUEL-KALAMAZOO PORPHYRY COPPER DEPOSIT
Juan Fajardo
San Manuel-Kalamazoo is a porphyry copper deposit that has been tilted and
dismembered due to Basin and Range dynamics. Although some cross sections
and structural reconstructions have been constructed (Lowell, 1968; Force,
Dickinson, and Hagstrum, 1995; Spencer et al., 2009), the technique of faultsurface map reconstruction (Seedorff et al., 2015) has never been undertaken in
this deposit. Three-dimensional surface projections of the main faults at San
Manuel have been generated using BHP-Magma historical database, composed
of 2,023 surface and underground holes, and historical underground working
maps (SRK, 2013), permitting a more accurate approach to the amount and
direction of slip. These surface maps are expected to be the base of a
preliminary structural reconstruction of the deposit.
The results of the mineral normalization the epidote in the San Manuel deposit
are also presented. A traverse of one kilometers within its propylitic halo
suggests that the epidote has low amounts of REE (X=0.0013), indicating that
allanite is not a relevant component (allanite samples presented by Armbruster at
al., 2006, have average values of REE equal to 0.579). The epidote component
seems to be the strongest (Fe Total average=0.945), and clinozoisite is not
observed. Manganese is interpreted as mainly Mn2+; therefore piemontite
component does not seem to be significant.
9
CONTRASTING STYLES OF LARAMIDE HYDROTHERMAL ALTERATION IN
THE SUPERIOR MINING DISTRICT, ARIZONA
Sean O’Neal
This ongoing study characterizes two previously unstudied hydrothermal systems
in the Superior mining district of central Arizona. Detailed alteration mapping, age
dating, and isotopic analysis of carbonates have provided insights into the
evolution of the systems and their genetic relations to other systems within the
district (the Silver King mine, the Magma mine, and the Resolution deposit).
Despite all of the systems being hosted in the same stratigraphic sequence and
likely being sourced from the same underlying batholith (the Schultze Granite),
they have all manifested themselves in drastically different ways. Fluid
temperature likely exerted the greatest influence over these differences, while
other contributing factors likely included the oxidation and sulfidation states of the
fluids.
Alteration mapping of hydrothermal systems near Woodcamp Canyon and King’s
Crown Peak within the western Superior mining district has identified mineral
assemblages and zoning patterns typical of the distal porphyry copper
environment. Alteration in the pelitic Pinal Schist and the quartzites of the
Apache Group rocks is dominantly intense quartz-sericite-pyrite alteration and
veining, and locally includes kaolinite and dickite. Limestones have been altered
to marble-garnet-vesuvianite, tremolite-quartz-talc-calcite, and serpentinemagnesite-calcite assemblages. A number of observed porphyry dikes are
strongly altered to quartz, pyrite, and sericite. Alteration assemblages and
intensities are highly controlled by stratigraphy. Some units display intense
alteration over kilometers along strike while others display weaker and less
continuous alteration. New U-Pb age dates have constrained the ages of the
mineralized system at the Silver King mine and the hydrothermal system by
King’s Crown Peak. The mineralized host at the Silver King Mine (the Silver King
Stock) yielded an age of 73 Ma. A granite porphyry dike located nearby the
King’s Crown hydrothermal system that demonstrably predates mineralization
yielded an age of 73 Ma, which constrains the age of the system to less than 73
Ma. Additional age dates are pending. Carbon and oxygen isotopic analyses
have revealed that altered limestones have experienced a shift towards lighter
values of both elements, which suggests that magmatic fluids played a crucial
role in the formation of the alteration observed.
10
K-METASOMATISM AS RELATED TO MANGANESE AND COPPER
DEPOSITS IN UPPER-PLATE TERTIARY SEDIMENTARY UNITS OF
CENTRAL-WESTERN ARIZONA
Christy M. Caudill
The largest known manganese deposit in the US is located in central-western
Arizona. Initial deposition of manganiferous sediments was followed by Cenozoic
extension in the southwestern US forming uplifts and basins through high- and
low-angle faulting. The paleoclimate surface conditions were distinctively arid,
producing basinal brines, an important factor in ore body formation here as
increased ligand capacity of the high-moderately saline waters assist in
transporting and concentrating metals. During extensional faulting and isostatic
uplift of lower-plate rocks, oxide mineralization occurred where reduced, metalbearing fluids ascended along detachment-related fault zones and mixed with
shallower oxidized, saline fluids. It has been hypothesized that volcanics and
sedimentary strata have been chemically altered through K-metasomatism and
are related to mineralized Tertiary detachment fault zones in the southwestern
US as a result of these mobilized reduced solutions. Smaller-scale geochemical
studies of volcanics have been done in central-western Arizona (e.g., a single
cooling unit studied by Hollocher, 1993) as the volcanic units are generally
accepted to be the likely source for these economic mineral deposits. Similar
alteration mineral assemblages (oxide- and alkali-rich, sulfide-poor, low Si/Fe
ratios) are observed over a huge area, extending possibly 400km (personal
comm., Jon Spencer, 2015) through central-western Arizona with porous and
permeable sandstone units being far more voluminous than volcanics (in the
Artillery, Buckskin, and Rawhide Mountains specifically), yet these units have not
been systematically studied for geochemical composition. This study undertakes
a large-scale geochemical analysis of these sandstones in nine smaller study
areas spanning approximately 300km2 along with targeted feldspar and vein
zoning petrography which support the timing and movement of faults, fluids, and
minerals and may determine if they were a source of mineralization of the Mn
and other ore bodies. This work seeks to better understand the complex
processes that have resulted in ore formation in this broad area by geochemical
modeling from extensive field-based chemical data, mass balance analysis,
alteration mineral distribution, paleo-fluid temperature and salinity from fluid
inclusion data, and textural and timing relationships as seen in veining.
11
CALC-SILICATE ALTERATION AND ORE CHARACTERIZATION OF THE SAN
XAVIER SOUTH-MISSION-PIMA SOUTH ORE BODIES, ASARCO MISSION
COMPLEX, PIMA COUNTY, ARIZONA: IMPLICATIONS FOR THE
OPTIMIZATION OF MOLYBDENUM RECOVERY
Sarah E. Baxter
The purpose of this study is to better understand the skarns and mineralization of
ASARCO’s San Xavier South (SXS)-Mission-Pima South (PS) orebodies, Pima
mining district. A secondary focus is to characterize the various types of
associated Mo mineralization. Previous work helped identify key areas for
mapping and sample collection. Alteration zonation and ore type characterization
was achieved using a combination of field and laboratory work.
The SXS, Mission, and PS ore bodies occur within calc-silicate altered (skarn or
tactite) calcareous, dolomitic, and siliclastic Upper Paleozoic sedimentary rocks
(Concha Limestone, Scherrer Quartzite, Epitaph Formation). Hydrothermal
features are part of a porphyry Cu(-Mo) system generated by quartz monzonite
stocks (QMP) (58-59 Ma). Alteration varies with protolith composition: Concha
Limestone is replaced by proximal massive garnetite to gnt ± cpx to distal wol (±
gnt) at the marble contact. Scherrer Quartzite converts to qtz-rich cpx-trem (± cal,
anhy) hornfels. The thin bedded, compositionally varied Epitaph Formation alters
to intercalated hornfels and skarns consisting of gnt, cpx, anhy and cal (± tremact).
High grade Mo mineralization generally occurs in two modes: 1) disseminated
masses in Cpx-Trem (± cal, anhydrite) hornfels, 2) trace amounts in gnt ± cpx
skarn locally closely associated with scheelite, and 3) as fracture controlled
mineralization. Vein paragenesis plays an important role in ore characterization,
which varies considerably throughout the deposit. In the QMP stocks, Mo occurs
intermediate and late in the veining sequence. In the Epitaph, Mo is generally
late and may be associated with Py and Cpy. In the lower portion of the PS
orebody, Mo veins are truncated by Py-Cpy veins in Anhydrite beds. In the
Concha and Scherrer, a complex array of Cu-Mo mineral assemblages occurs
and timing is difficult to discern. In these lithologic units, generally, early Qtz-Cpy
± Py veins are cut by Mo ± Cpy veins truncated by Qtz-Epi-Cpy-Py ± Anhydrite
veins.
From this study, the relationships between mineral assemblages provide the
framework for a broad time-space relationship of zonation. The results also
identify deleterious mineral assemblages in specific lithologies associated with
Mo to help predict potential milling issues.
12
THE DISTRIBUTION OF RHENIUM CONCENTRATIONS AT THE BAGDAD
PORPHYRY CU-MO DEPOSIT
Christian Rathkopf
Rhenium, though rare in the Earth’s crust (0.4 ppb), is observed in many types of
ore deposits at a wide range of concentrations within the crystal structure of
molybdenite—commonly between 0 and 2,000 ppm. It is hypothesized that
variance in [Re] among Mo-bearing ore deposits may be causally associated with
other geologic attributes such as deposit type, lithology, alteration style, and
overall metal content. With a greater understanding of the relationship between
[Re] and these attributes of deposits, measurements of [Re] in molybdenite could
become a viable tool for mineral exploration. To test this hypothesis, the
distribution of [Re] in molybdenites was examined at the Bagdad porphyry Cu-Mo
deposit using high-precision electron microprobe analyses.
324 analyses were conducted on 45 Mo-bearing samples from Bagdad. [Re] in
molybdenite ranged from 0 to 4,450 ppm. Of the 11 lithologies sampled, the
lowest relative variance in [Re] was observed in the Precambrian mafic schist
([Re]=192, σ=128 ppm; n=13), and the highest in the quartz monzonite breccia
([Re]=664, σ=1360 ppm; n=10). Additionally, no correlations were observed
between [Re] and various degrees and styles of potassic and serecitic alteration
assemblages. Even individual molybdenite grains showed significant variation in
[Re]. All grains analyzed in 5 or more locations showed an average relative
standard deviation of 58%.
Preliminary results at Bagdad corroborate a wide range of [Re] within single
deposits, as well as a high degree of variation among host lithologies, alteration
assemblages, and even individual crystals. It would appear that a greater
understanding of variance in the distribution of [Re] in molybdenite at the
individual grain scale is a necessary first step before an extrapolation of these
data can be made into a viable tool for exploration.
13
HISTORY AND GEOLOGY OF THE GLOVE MINE, SANTA CRUZ COUNTY,
ARIZONA: MINING TO MINERAL COLLECTING
J.D. Mizer
Arizona has often been referred to as a mineral collector’s paradise. Collectors
place value on specimens for their physical characteristics as well as
provenance. Famous mine localities such as Bisbee, Morenci, and Ray have
produced spectacular specimens of cuprite, azurite, malachite, and native
copper. Another important contributor to beautiful, and often sought-after, mineral
specimens are the smaller replacement or vein-type deposits. Famous localities
such as Red Cloud, Rowley, Old Yuma, 79, Hilltop, and the Glove have produced
magnificent specimens of wulfenite and some continue to do so today to the
more determined collectors.
Located in Pima County, the Glove Mine sits in the Tyndall mining district on the
southwest corner of the Santa Rita Mountains. The property was originally
claimed in 1907 and mined for silver, lead, and zinc from 1911 to about 1927.
During the 1950s the discovery of a significant body of oxidized lead ore drove
productivity at the mine deeper into the earth. As an oxide mineral, wulfenite was
common in large quantities throughout the descending ore body. Mineral
collecting at the Glove was prominent during this time, with collectors like Dick
Apfel, Richard Bideaux, Richard Jones, and Edward Mack leading the initial
efforts. The oxidized ore was quickly mined out, but it was mineral collecting that
drove exploration efforts at the Glove to modern times.
New geologic evidence (mapping and U-Pb ages) shed light on the formation of
the ore body at the Glove. The ore sits in locally brecciated limestone along the
east-west Glove fault zone between a 75.5 Ma latite porphyry sill to the north and
a mass of 169.5 Ma quartz monzonite to the south. Mineralizing fluids, likely from
a distal source, exploited this zone and locally replaced favorable carbonate beds
within the Permian Earp formation with hypogene galena, sphalerite, and minor
chalcopyrite. Subsequent oxidation of these sulfides resulted in enrichment of
lead and zinc oxide minerals. Mining activity and mineral collecting was confined
to the footwall (south) side of the sill. No geologic constraints other than the
location of the Glove fault have been placed on the restriction of ore formation in
this area, leaving the north side of the sill largely unexplored.
14
Geophysics
MORPHOLOGY, TIMING AND INTERPRETATION OF CYLINDRICAL
FEATURES IN 3-D SEISMIC DATA FROM THE GUINEA PLATEAU, WEST
AFRICA
Clinton Koch
Two distinct phases of volcanism are recorded in geophysical data from the
Guinea Plateau, offshore West Africa. Albian volcanism in the region is attributed
to the rifting between Africa and South America and younger Late
Cretaceous\Early Paleocene volcanism may be associated with crustal
weakening due to the intersection of two fracture zones related to rifting. Detailed
mapping of 3-D seismic data on the Guinea Plateau using a semblance attribute
highlights numerous cylindrical to elliptical anomalies associated with this
volcanism and dissolution features. The majority of these anomalies range in
diameter from 1 – 2.5 km with a few larger anomalies from 5 – 20 km. The
cylindrical structures have interpreted ages ranging from the Aptian to early
Paleocene. These ages have been interpreted using seismic onlap relationships,
isopach analysis, and seismic attributes. Six different morphologies have been
identified on the basis of reflection geometry and amplitude character and are
used to aid interpretation. Circular gravity anomalies, coupled with well and
seismic data, indicate features that are interpreted as post-rift buried seamounts
and syn-rift volcanoes. Many of the cylindrical features that surround these
gravity anomalies potentially are sills and flows associated with the volcanism.
The post-rift features are capped by a Paleocene unconformity indicating a late
Cretaceous emplacement age. Rose diagrams of the elongation direction of the
elliptical cylinders show two dominant directions of elongation, a northeast and a
southeast direction. The northeast elongation direction is prominent in the postrift section and appears to be related to a series of northeast-trending normal
faults from an extensional episode in the Cenozoic. The southeast elongation
direction appears dominant in the rift-aged section and may be related to
southeast-striking rift-related normal faults. The southeast direction may also be
influenced by gravitationally-induced extension parallel to the evolving margin.
15
INVESTIGATION OF VERTICAL CRUSTAL MOTION USING GPS
Alexandria Will-Cole
In this study, we measured vertical crustal deformation along the east coast of
the United States by analyzing global positioning system (GPS) data from over
200 geodetic stations along the margin of the North American east coast. This is
the largest network catalogued to date to monitor glacial isostatic adjustment
(GIA) in this region. Our analysis of the GPS data reveals that a portion of the
coastline is subsiding at rates in the range of -7.0 to -2.50 mm/yr. The estimated
vertical subsidence rates support the hypothesis that the east coast is
undergoing glacial isostatic adjustment. Furthermore, these vertical rates give us
insight into the rheologic properties of the mantle beneath the east coast of the
U.S. The subsidence of the coast also contributes to the rapid sea level rise
there. The next step is to explore different GIA ice models, using the
computational infrastructure for geodynamics supported code Selen to develop a
refined model for North America GIA constrained by our GPS measurements.
16
TOPOGRAPHIC CONTROLS ON SOIL AND REGOLITH THICKNESS FROM
SHALLOW-SEISMIC REFRACTION CONSTRAINTS ACROSS UPLAND
HILLSLOPES IN THE VALLES CALDERA, NEW MEXICO
Jared Olyphant
How rock is weathered physically and chemically into transportable material is a
fundamental question in critical-zone science. In addition, the distribution of
weathered material (soil and saprolite) across upland landscapes exerts a firstorder control on the hydrology of watersheds. In this study we collected six
shallow seismic-refraction surveys in the Redondo Mountain region of the Valles
Caldera, New Mexico. The P-wave velocities corresponding to soil (300 ms^(-1)
≤ V_p ≤ 700 ms^(-1)) were inferred from a seventh seismic line where soilthickness data were determined by pit excavation. Forward modeling was used
to infer the P-wave velocities corresponding to saprolite (700 ms^(-1) < V_p ≤
2000 ms^(-1)) and fractured but relatively unweathered bedrock (> 2000 ms^(1)). Using multivariable regression, we quantified the influence of slope gradient,
aspect, and topographic wetness index (TWI) on soil and regolith (soil plus
saprolite) thicknesses. Our results show that both soil and regolith thicknesses
vary inversely with slope gradient and TWI while varying directly with slope
aspect. Within these results, we find TWI consistently exerts dominant control on
regolith thickness variations and usually, but not always, variations in soil
thicknesses. Slope aspect is mostly secondary, and, excluding steep slopes,
gradient often provides no additional value to TWI for explaining variations in
saprolite thicknesses. Using an empirical model based on power-law
relationships to predict soil and regolith thicknesses, we were able to fit our
inferred thicknesses with R^2-values as great as 0.697 for soil and 0.804 for
regolith in areas with significant topographic variations. These results further
demonstrate the power of shallow seismic refraction acquisition in providing
spatially extensive datasets for determining the structure of soil and regolith and
they add to a growing body of knowledge on how soil and regolith are distributed
across upland landscapes.
17
PRELIMINARY DEEP TOMOGRAPHIC IMAGING OF THE SOUTHERN ANDES
SUBDUCTION ZONE
Daniel Evan Portner
The geometry of the deep Nazca slab is poorly constrained south of the Chilean
flat slab due to a lack of prominent earthquake activity. Although recent
tomography results are beginning to reveal the structure of the southern Nazca
slab, many interesting features, such as a potential relic slab and the slab's
interaction with the transition zone, are left poorly resolved and without a
connection to processes occurring further north. Here I present preliminary
results from a finite frequency teleseismic tomography inversion of P-wave arrival
time residuals. I use stations from several different temporary and permanent
networks throughout Chile and Argentina between latitudes 24S and 42S,
providing a high resolution image from ~200km depth through the mantle
transition zone of the subducting Nazca slab and the surrounding asthenosphere.
Using these results, I constrain the Nazca slab geometry and compare alongstrike variations in the Chilean subduction zone.
18
RAPID GEODETIC SHORTENING ACROSS THE SANTA BARBARA AND
EASTERN CORILLERA OF NORTHWEST ARGENTINA AS MEASURED BY
THE PUNA-ANDES GPS ARRAY
Phillip McFarland
The Puna-Andes GPS Array (PAGA) is a continuously recording GPS (cGPS)
network operating in northwest Argentina between roughly 24S and 26S latitude.
PAGA comprises two five-station phases: phase 1 deployed in March 2009 and
phase 2 deployed in August 2013. We present velocities from PAGA phase 1
realized in a South America fixed reference frame with 79 (16) global (itrf08
reference) cGPS stations spanning the period between August 2009 and August
2013. We evidence cumulative crustal shortening at a rate of 8.6 ± 0.1 mm/yr
across the Puna, Eastern Cordillera and Santa Barbara provinces with the
systematic eastward decrease in thrust front perpendicular velocities from 11.8 ±
0.1 mm/yr near the Western Cordillera to 3.2 ± 0.1 mm/yr near the modern thrust
front. We invert the thrust front perpendicular velocity field using a simple edge
dislocation model and find a shear interface rooted beneath the Eastern
Cordillera slipping freely at a rate of 10.2 mm/yr below 25 km depth and dipping
20° to the northwest. We link our best-fit model to a shallowly dipping
décollement under the Santa Barbara system using a multiple dislocation model
constrained by fault geometries inferred from balanced cross sections and
compare model derived stress and strain fields with large wavelength
topographic features and observed seismicity.
19
20,000 METERS AND MORE UNDER THE CRUST
Jamie Ryan
On the west coast of Central South America, the subducting Nazca slab extends
through the mantle transition zone and penetrates the 670 km discontinuity. We
use broadband data collected in two deployments (CAUGHT and PULSE) in the
north central Andes to image the 410 and 670 km discontinuities using receiver
functions (RF) and compare our results to previous travel time tomography
studies done by the Global Seismology and Tectonics (GSAT) group.
We use low-frequency P-wave and S-wave RF analyses to identify these mantle
discontinuities. The P-wave and S-wave RF methods isolate P-to-S and S-to-P
conversions, respectively, from these mantle discontinuities. S-wave RFs have
the advantage of no multiples arriving and interfering with the primary arrivals,
but are restricted to a narrow distance range (60-85º) where the conversion is not
contaminated by other phases (Yuan, et al., 2006). By combining the two RF
methods, we can compare the larger P-wave RF and the multiple-free S-wave
RF data-sets to create more robust models of the transition zone.
Our results show a relatively consistent 410 km discontinuity that shows
disruption at locations where the subducting slab penetrates and appear to
correspond to the dip angle of the slab. In the north, under Peru, there is an ~85º
dip and the slab decreases the amplitude of the discontinuity by about 50%. To
the south, under Bolivia, a normal dip angle of ~30º appears to significantly
depress or reverse the amplitude of the discontinuity over an area of 250 km or
more as it passes through. Along the dense line of the CAUGHT array, it appears
that the slab may have an opposite effect on the 670 km discontinuity, as the
highest topography on that boundary appears along the track of subduction. This
is in contrast to observed global behavior, which associates depression of the
410 and elevation of the 670 km discontinuity with regions of higher temperature
or mantle plumes.
20
AMBIENT NOISE TOMOGRAPHY ACROSS THE ALASKAN CORDILLERA
Kevin M. Ward
The Alaskan Cordillera has formed though an aggregate of tectonic processes
including normal subduction of pacific lithosphere, flat-slab subduction of the
Yakutat microplate, and the accretion of allochthonous terranes among other
processes. Large active strike-slip faults, high levels of seismicity, and volcanic
activity demonstrate the ongoing dynamic nature of the orogen. Many of these
tectonic processes significantly alter the structure of the overriding lithosphere
making this section of the North American Cordillera a unique place to study
active orogenic processes as recorded in the lithosphere. Over the last decade,
ambient noise tomography has emerged as powerful tool for imaging the
lithosphere on orogenic scales often from ‘legacy’ data sets. I present the results
of an extensive data mining effort integrating 197 permanent and temporary
seismic stations into an ambient noise study across southern Alaska and
westernmost Canada. I measure the surface wave dispersion of Rayleigh waves
extracted from the ambient seismic wavefield for 13 periods between 8 and 50
seconds. Special care is administered when quality controlling and processing
the data, an especially important consideration in regions with high levels of
seismicity.
Principal observations of my tomography model are largely consistent with
mapped geology features and previous geophysical studies while providing
previously unavailable, laterally continuous details of the Alaskan Cordillera
lithosphere. At shorter periods, low velocities observed under the Prince William
and Yakutat terranes, and apparent north-northwest migration of these low
velocities are consistent with uplift of the Chugach Mountains through
underplating of sediments beneath the Chugach terrane. At intermediate periods,
a geophysically uniform crust is observed north of the Denali fault and is
consistent with a sharp transition in crustal thickness. Under the Wrangell
volcanic belt, a prominent low velocity anomaly correlates well with the lateral
extent of a relative low gravity anomaly and Neogene surface volcanics. At
longer periods, a low velocity anomaly bounds the inferred eastern extent of the
subducted Yakutat microplate beneath the Wrangell volcanic belt. I suggest this
low velocity feature represents the upper mantle melt regime that sources the
volcanism in the Wrangell volcanic belt.
21
THE PAST AS THE KEY TO THE FUTURE: USING PALEOCLIMATE
RECORDS TO INFORM RISK OF INDIAN MEGADROUGHT
Garrison Loope
Variability in monsoon precipitation occurs on all time scales and has severe
consequences for the people who depend on monsoon rains. The most recent
model projections show monsoon precipitation and variability of precipitation
increasing over the 21st century. This is expected to cause both increased
flooding and severe droughts. Although current models are able to capture the
risk of relatively short droughts (1-5 years) reasonably well, they tend to
underestimate the risk of longer, decadal-multidecadal droughts. I use
instrumental records from India in conjunction with cave, tree ring, and ice core
data from the NOAA paleoclimate database to reconstruct late Holocene
monsoon variability. Using a combination of paleoclimate and instrumental data, I
am able to show that the Indian monsoon has more low-frequency variability than
is projected by current climate models. The growing evidence for this
discrepancy in hydroclimate variability between models and
observational/paleoclimate records is of grave concern. If these models fail to
capture the decadal-multidecadal droughts of the past it is likely they will
underestimate the possibility of such droughts in the future. I use simple Monte
Carlo simulations to combine the robust outputs of climate models (mean and
variance) with those of paleoclimate (frequency distribution) in order to estimate
probabilities of decadal and multidecadal droughts over the next 50 years. I find
that incorporating the long-period variability into these simulations from
paleoclimate records causes the risk of multidecadal droughts to nearly double.
Although there are numerous inherent assumptions in these simple probabilistic
models, they may be more realistic than most state of the art climate models for
risk of multidecadal droughts.
22
TAKING THE OCEAN’S TEMPERATURE: GALÁPAGOS CORALS AND
CHANGES TO ENSO
Gloria Jimenez
The El Niño-Southern Oscillation (ENSO) is regarded as the strongest source of
global climate variability from year to year. However, fundamental questions
remain concerning ENSO’s variability, even over the twentieth century. In this
study, we present a new coral record of sea surface temperatures (SSTs) from
the Galápagos archipelago, which sits in the eastern Pacific at the epicenter of
the changes associated with a canonical El Niño episode. This record is novel as
it is nearly continuous, with monthly-resolved growth spanning the strong El Niño
episodes of 1982-83 and 1997-98. Coral Sr/Ca ratios closely mirror instrumental
SSTs over the past century, and highlight a warming trend as well as a pattern of
higher-amplitude SST variations since 1990, suggesting that radiative forcing
may be increasing the strength of ENSO events in the eastern Pacific.
23
PACIFIC SEA LEVEL RISE PATTERN AND GLOBAL WARMING HIATUS
Cheryl Peyser
Since the late 1990s, Earth’s surface temperatures and regional sea level rise
(SLR) exhibit two notable features: a slowdown of global warming (hiatus), and
an East-West seesaw pattern of SLR in the Pacific. To investigate their possible
linkage, we use ocean temperature and sea-level observations along with climate
model experiments. Analyses of thermosteric sea-level and ocean heat content
(OHC) trend confirm the importance of ocean heat uptake below the surface
layer during a warming hiatus. Notably, the subsurface layer (100-300m) of the
Pacific shows significant basin-wide increase in OHC along with a strong EastWest gradient that is reflected in the Pacific SLR pattern. Control simulations
from 35 CMIP5 and 10 GFDL models indicate that during periods of negative
trend in global mean temperature (analogous to hiatus decades in a warming
world), dynamic sea level increases in the Western Pacific and decreases in the
Eastern Pacific. The opposite occurs during periods of positive temperature
trends. These results suggest that a possible flip of the Pacific SLR seesaw could
imply a resumption of surface warming and SLR acceleration along the U.S.
West Coast.
24
3-POLE SOIL GENESIS INITIATIVE: A GLOBAL APPROACH TO CITIZEN
SCIENCE
Yadi Wang
The geosciences offers numerous opportunities for scientists to adventure
undiscovered places and to ask large-scale questions in various fields. Among all
the topics, climate change has drawn the most attention and become a global
concern. Comparing to lower lands, alpine and polar regions normally undergo a
more vigorous weathering process due to unique climate conditions. With more
sensitive weathering, these regions tend to respond faster to climate change than
lower lands. However, because the majority of these regions are inaccessible to
most scientists and general public, major questions such as how soil genesis
progresses in the extremely cold environments and how it responds to global
climate changes have not been able to address. An innovative platform of
adventure science aims to help scientists access samples collected by explorers
from unreachable places to answer undiscovered questions.
3-Pole Soil Genesis initiative attempts this challenge by pairing with trained
adventurers so that we could most effectively answer soil genesis of collected
rocks from a large geographical gradients along altitude and latitude during
climate change. Collaboration with Adventurers and Scientists for Conservation
(ASC) has been established since 2011. A total of 13 locations of rock samples
were collected from all continents except Australia. This wide sampling range
allowed us to study the behavior of surface and subsurface of these rocks in
geochemical perspectives with technique such as portable X-ray fluorescence
and synchrotron transmission X-ray diffraction. These techniques can assist us to
predict chemical composition and mineralogical alteration. Electron microprobe
can be furthermore employed to resolve weathered mineralogy. All work will
provide insights in understanding the association between geochemical
processes and climate change in these unique regions.
Aside from scientific achievements, this collaboration has provided opportunities
for explorers to contribute works into science community. While new scientific
merit are obtained, preliminary information can be delivered to those explorers
and extended to general public in order to improve outreach consequences. This
adventure science platform will ultimately aid in efficacy of globe citizen science
as means of generating new information as well as understanding and protecting
our fragile Earth system.
25
IDENTIFYING SOURCES OF LOCAL SPRINGS IN THE COLORADO RIVER
DELTA USING STABLE ISOTOPES
Hector A. Zamora
The Cienega de Santa Clara (CSC) is the largest wetland on the Mexican portion
of the Colorado River Delta (CRD). This wetland is supported by brackish
groundwater from the Wellton-Mohawk Irrigation and Drainage District in Arizona
and in minor percentage by local springs. The origin and hydrology of the local
springs remains uncertain. Distinguishing the several sources of water in the
CRD becomes increasingly important to manage not only agricultural resources,
but also the natural spaces remaining in the area. For this study, I analyzed
water samples for δ18O, δD, 3H, 14C, and major ion chemistry. These samples
were collected from several locations within the CSC, local springs, wells, and
Colorado River at Yuma. Stable isotope results (δ18O vs δD) for the CSC and
Colorado River plot in an evaporation trend with a slope ~5.78. Spring water
samples plot near this evaporation trend, but with relatively higher δ18O and δ2H
values than CSC and well water. 3H activity from a spring sample resulted in
>0.5 TU. This activity is far below modern Colorado River water (7-8 TU). 14C
analysis for three spring samples yielded 14C PMC of 24.9, 11.7, and 2.9 from
north to south along the flow path. These results suggest that water from the
springs and local wells is Colorado River water. The low 3H activity and low 14C
PMC obtained from the spring samples indicate the spring system is not currently
being recharged by the river. The origin of spring water is interpreted to be old
and evaporated Colorado River water ponding on the surface and infiltrating into
the local groundwater reservoir prior to the construction of dams upriver.
26
INVESTIGATING THE TIMING OF MELT-PRODUCING HIGH GRADE
METAMORPHISM IN THE RUBY RANGE, SOUTHWESTERN MONTANA
THROUGH ZIRCON U-PB GEOCHRONOLOGY
Mariah C. Romero-Armenta
The Montana Metasedimentary terrane of southwestern Montana is one of three
regions that compose the Wyoming craton (Mogk et al., 1992; Meuller et al.,
1993; Roberts et al., 2002). Past studies suggest three main metamorphic events
affected this terrane; these metamorphic events occurred at ~2.7 Ga, ~2.45 Ga,
and ~1.78 Ga (Cheney et al., 2004; Erslev and Sutter 1990; James and Hedge,
1998; Jones 2008; Mueller et al., 2004; Roberts et al., 2002). The Ruby Range, a
basement-cored Laramide uplift, is located to the east of Dillion, Montana. The
Pre-Cherry Creek Group, Dillion Gneiss, and Christensen Ranch Group are three
northeast-southwest trending Precambrian suites that make up the Ruby Range.
Over the last few decades, relatively few analyses of zircon U-Pb geochronology
have been conducted in the Pre-Cherry Creek, Dillion Gneiss, and the
Christensen Ranch suites. Thus, placing constraints on the timing of
crystallization and metamorphism in the Ruby Range will provide an enhanced
understanding of the relationship between the three suites.
The goal of the project was to collect and analyze neosomes and mylonitic
garnet leucogneisses from the three suites in the range to determine if the
metamorphism event at 1.78 Ga was hot enough to produce any partial melt in
sampled rocks. This study presents 207Pb/206Pb ages from five samples
collected from the Pre-Cherry Creek, Dillion Gneiss, and Christensen Ranch
suites located in the Ruby Range. Backscattered Electron (BSE) and
Cathodoluminescence (CL) imaging of the zircons from the range document the
presence of cores with multiple zoned thick overgrowths. Due to the complexity
of the zircons from each sample, BSE and CL imaging is essential in determining
which spots on the grains to ablate. Preliminary results from applying Laser
Ablation-Multicollector-Inductively Coupled Plasma-Mass Spectrometry (LAICPMS) for zircon U-Pb geochronology consists of two samples collected from
the Dillion Gneiss. Sample 14-MA-11, a mylonitic garnet leucogneiss, located in
the Dillion Gneiss indicates igneous ages of ~2.4 Ga and ~2.5 Ga. Sample 14MA-06, neosome from a pelitic gneiss within the Dillion Gneiss, yields an igneous
age of ~2.45 Ga. The results of these two samples from the Dillion Gneiss
provide a more detailed description and understanding of the geological history in
the Ruby Range.
27
(U-TH)/HE AND U/PB THERMOCHRONOMETRY AND U/PB
GEOCHRONOMETRY OF EXPOSED BEDROCK OUTCROPS IN THE
WINDMILL ISLANDS, ANTARCTICA
Patrick Boyd
With 98% of Antarctica covered in ice sheets it is the least explored continent on
earth. The Windmill Islands in East Antarctica are part of the 2% of Antarctica
that isn’t encapsulated by ice, and the only such outcrop for hundreds of miles in
any direction. Valuable inferences can be made about the Windmill Islands and
the surrounding Wilkes Land regions history through analysis on the exposed
bedrock. High and low temperature apatite thermochronometers (U-Th)/He and
U-Pb and U-Pb zircon geochronometry can give us a constrained thermal history
of exposed bedrock outcrops in the Windmill Islands, Antarctica. By performing
chronometry techniques on multiple granites, gneisses, and diorites from the
areas bedrock, inferences can be made regarding the crystallization and cooling
history of the coast of this area of Wilkes Land, East Antarctica. Crystallization
ages seen in U-Pb zircon data will allow us to view the last major thermal event
in the area, while high and low temperature thermochronometry data will allow us
to know the timing of metamorphic events in the region as well as the erosional
history in the Windmill Islands. This data will make it possible to better
understand the tectonic history of the Windmill Islands and surrounding Wilkes
Land region, and will ultimately lead to a more complete picture of the role
eastern Antarctica has played in earth’s tectonic history.
28
ZIRCON (U-TH)/HE AGE-EU CORRELATIONS REVEAL THERMAL HISTORY
OF LAURENTIAN BASEMENT OVER PAST 1.3 BILLION YEARS
Devon A. Orme
We use zircon (U-Th)/He thermochronology to constrain the ProterozoicPhanerozoic thermal history of Laurentian basement in the northern Rocky
Mountain region, western United States. We present the first zircon (U-Th)/He
ages of Wyoming craton crystalline rocks from the hanging walls of major
Laramide faults in the Wind River Range (54 ages) and Bighorn Mountains (32
ages). All samples show a strong negative correlation between zircon He age
and effective Uranium (eU), with younger ages from the Wind Rivers forming a
“pediment” at ~ 50 Ma over a wide range of high-eU values. Using the span in eU
as a first-order proxy for relative differences in the degree of radiation damage
among grains, we use a zircon radiation damage and annealing model
(ZRDAAM) that accounts for the effects of radiation damage on He diffusion in
zircon to document a multistage thermal history of our samples. The thermal
history that best models the observed ages for the Wind River dataset consists of
initial cooling beginning at 1300 Ma, followed by reheating to 160 °C at 60 Ma,
and subsequent cooling to 75 °C during Laramide orogenesis. Our best model for
the Bighorn dataset consists of initial cooling between 1300 and 1100 Ma (500 to
100 °C), followed by reheating to 135 °C prior to final exhumation at 70 Ma.
These thermal histories are consistent with prior apatite He and AFT constraints
for the timing of Laramide exhumation in the Wind Rivers (60 Ma) and Bighorn
mountains (70 Ma). Importantly, our model constrains Proterozoic cooling and
subsequent reheating prior to Laramide exhumation. This timing is consistent
with mid-late Proterozoic tectonism associated with the Grenville orogeny (ca.
1300-980 Ma), further exhumation associated with the formation of the Great
Unconformity, and burial by passive margin and foreland basin sedimentation
during the Paleozoic and Mesozoic. This long-duration, Proterozoic-Phanerozoic
thermal history was previously unrecognized by lower-temperature
thermochronometers and our data provide some of the first in situ evidence of
Proterozoic tectonism in the northern Rocky Mountain region.
29
LOW-TEMPERATURE THERMOCHRONOLOGY OF LARAMIDE RANGES IN
MONTANA INDICATE CRETACEOUS EXHUMATION ASSOCIATED WITH
EARLY LARAMIDE TECTONICS
Mariah C. Romero-Armenta
Timing of exhumation of Laramide basement uplifts can be used as a proxy for
timing of thick-skinned deformation resulting from lithospheric scale (e.g. flat-slab
subduction) related processes. Thick-skinned deformation in the Laramide
province ultimately resulted in the disruption of the regional foreland basin.
Despite its significance, the timing and pattern of Laramide deformation remains
poorly constrained particularly in Montana. Thermochronological data from
Wyoming indicate exhumation of Laramide ranges during the late Cretaceous
and Paleogene. Whereas a few data exist for the Beartooth Range in Montana;
the exhumation history of most of the Montana ranges remains unexplored
preventing testing of current tectonic models.
This study presents the first detrital fission track study from Montana that
combined with in-situ AFT ages of basement rocks characterized the regional
exhumation history of Laramide ranges in Montana. We report apatite fission
track thermochronologic (AFT) data from modern river sands derived from
Laramide ranges, bedrock basement samples, and a syn-orogenic conglomerate
clast to determine the regional exhumation history of the Beartooth, Gravelly,
Madison, Tobacco Root, Ruby, the Highland Mountains, in Montana. Whereas
AFT central ages are mostly Paleocene-Eocene thermal modeling show a strong
Cretaceous signal and slow cooling for most of the Cenozoic. This is in stark
contrast with the thermal history of other Laramide ranges such as the Wind
River Range in Wyoming.
30
CALIBRATING TRACE ELEMENT PROXIES FOR CRUSTAL THICKNESS OF
MAGMATIC ARCS: SR/Y AND LA/YB
Lucia Profeta
There is a growing interest in tracing the crustal thickness of arcs during their
evolution. In part this is driven by the need for better understanding of long-lived
convergent margins, but it also has economic applications: for example porphyry
copper deposits are found in relationship to magmas from thick arcs.
Subduction related magmas form as a result of complex interactions between
asthenospheric mantle-derived melts and melts from the overriding plate. It has
been hypothesized that the ratios of Sr/Y and (La/Yb)N in arc intermediate
magmas correlate with the crustal thicknesses beneath arcs (e.g. Kay and
Mpodozis, 2001). Higher ratios indicate equilibration of these arc magmas with
garnet and amphiboles, typical for deeper levels of thick crust, whereas lower
values are indicative of plagioclase being a major fractionating phase. One of
these ratios (Sr/Y) has been shown to positively correlate with Moho depths in
Quaternary arcs over a large spectrum of igneous compositions (Chiarardia,
2015), but it is not clear if that same correlation applies to intermediate rocks, or
if that signal is carried by mafic compositions only. Here we use compilations of
geochemical data of arc volcanoes and crustal thicknesses to show that both of
these ratios correlate at global scale with crustal thickness in 19 modern arcs.
The La/Yb –crustal thickness correlation is better defined. One possible
complication for the Sr/Y system is that some thin arcs display elevated ratios,
suggesting that in those cases slab melting can influence this parameter. The
same relationships appear to hold at regional scale for the two arcs where crustal
thickness varies significantly along strike: the northern part of the Southern
Andean Volcanic Zone and the Trans Mexican Volcanic Belt.
The empirical correlation from modern systems was then applied to estimate
variation in crustal thickness in the Cordilleran Interior of Western North America
from the Jurassic to the Miocene. Overall, results are consistent with
independent estimates of regional crustal thickness.
References
Chiaradia, M., 2015, Crustal thickness control on Sr/Y signatures of recent arc
magmas: an Earth scale perspective: Scientific Reports, v. 5, no. 8115.
Kay, S.M. and C. Mpodozis, 2001, Central Andean ore deposits linked to
evolving shallow subduction systems and thickening Crust, GSAToday, v. 11, no.
3, 4-9.
31
SYNOROGENIC RECORD OF BASIN REORGANIZATION IN THE SIERRAS
PAMPEANAS REGION OF ARGENTINA
Andrea Stevens
The Sierras Pampeanas region of Argentina is characterized by thick-skinned
deformation that includes 12 basement cored peaks that reach as high as 6km.
The rise of these basement block uplifts have commonly been attributed to a
craton-ward transference of stress triggered by the initiation of flat slab
subduction. In this study, we focus on synorogenic fluvial deposits located in
basins adjacent to basement block uplifts. Detailed sedimentology from
measured sections from Vinchina, La Rioja, Argentina and La Troya, Catamarca,
Argentina coupled with detrital zircon geochronology from sandstones and
intercalated tuffs constrain the temporal and spatial patterns of the rise of the
Sierras Pampeanas. We hypothesize that uplift of the Sierras Pampeanas ranges
fundamentally altered the provenance source, flow direction, and fluvial
architecture of these deposits. An abrupt change from thick channelized fluvial
deposits to thin paleosol horizons supports a major change in the regional basin
history between 12 and 9 Ma, and could mark the initiation of flat slab
subduction. We compare the timing of basin reorganization with new data
acquired from apatite fission track and apatite helium thermochronology that
records the spatial and temporal exhumation history of nearby basement block
uplifts.
The presence of a modern flat slab beneath west-central Argentina provides an
unprecedented opportunity to link lithospheric-scale processes with its
manifestation on surface geology. This relationship is important in interpreting the
geological history of areas where the slab orientation is no longer preserved.
32
INDIAN CONTINENTAL MARGIN SUBDUCTION, HIGH-PRESSURE, LOWTEMPERATURE METAMORPHISM AND SYNCONVERGENT EXHUMATION
DURING INDIA-ASIA SUTURING, LOPU KANGRI RANGE, SOUTH-CENTRAL
TIBET
Andrew K. Laskowski
The Lopu Kangri range, located ~50 km NW of Saga, Tibet, exposes YarlungTsangpo suture zone architecture in the footwall block of a NW-SE oriented
horst. In the south-central portion of the range, metasedimentary rocks (calcparagneiss, paragneiss, schist, and quartzite) are exposed in an antiformal
structural culmination mantled by accretionary wedge mélange. Detrital zircon
geochronology of these rocks indicates that they correlate to the Tethyan
Himalaya sequence, which was deposited on the passive northern margin of
India prior to collision with the southern margin of the Lhasa terrane (Asia).
Electron microprobe geochemical analysis reveals the characteristic mineral
assemblage quartz, phengitic white mica, chlorite, albite, rutile, apatite, zircon +/calcite, tourmaline, allanite, titanite, hornblende, biotite, spessartine garnet, and
ilmenite. Peak pressures and temperatures of metamorphism were calculated for
two samples—a garnet-bearing whiteschist and a phengite chlorite albite schist—
using phengite geobarometry, Zr in rutile geothermometry, and garnet-phengite
Fe-Mg exchange geothermometry. The pressure dependence of Si enrichment in
phengitic white mica was constrained using composition-specific equilibrium
phase diagrams (pseudosections). Our results indicate that meta-Tethyan rocks
reached peak pressures of 20-25 kbar at temperatures <550 C (eclogite facies),
which is consistent with continental margin subduction to upper mantle depths
within a relatively cold subduction channel. These rocks experienced
amphibolite-upper greenschist facies retrograde metamorphism during
synconvergent exhumation to mid-crustal depths. Finally, they were exhumed in
the footwall of a set of NW-SE normal faults related to Miocene-recent orogenparallel extension. This study is the first to document Indian-affinity, HP
metamorphic rocks in the Yarlung-Tsangpo suture zone of southern Tibet,
lending credence to geodynamic models of the India-Asia collision that
extrapolate findings from Tso Morari, in NW India. In addition, this locality
provides a unique opportunity to study the phenomenon of continental
subduction, HP metamorphism, and rapid synconvergent exhumation along the
central segment of the India-Asia suture.
33
SEDIMENTOLOGY, PROVENANCE AND GEOCHRONOLOGY OF A SUTURE
ZONE SUCCESSOR BASIN, INDIA-ASIA COLLISION ZONE, TIBET
Simon Stickroth
We investigated a previously undocumented sedimentary section exposed along
the north flank of the Indus-Yarlung suture zone (IYSZ) in Tibet, between the
Xigaze forearc basin and the Gangdese batholith. This 664m section consists of
three major units. The section fines upward from matrix- and clast-supported
granite boulder conglomerates to massive sandstone and mudstone beds,
capped by another series of matrix- and clast-supported volcaniclastic cobbleboulder conglomerates interbedded with dirty limestones and a tuffaceous unit.
This formation was deposited in alluvial-fan and fluvial depositional systems.
Conglomerate clast-counts suggest the basin was sourced from the Gangdese
magmatic arc in the north, and changed upsection to a dual-sourced basin with a
marked increase in input from the IYSZ and Tethyan Himalaya to the south.
Preliminary chronostratigraphic age control from zircon U-Pb geochronology
suggests the basin is Eocene in age and may represent a post-collisional
successor basin to the Xigaze forearc. This basin can potentially provide unique
insight into the immediate post-collisional history of the IYSZ.
34
POST-INDIA-ASIA COLLISION RISE OF THE HIMALAYA FROM TIBETAN
PALEOSOLS
Ryan J. Leary
The post-collisional uplift history of the India-Asia suture zone in southern Tibet is
important for understanding the geodynamic conditions of collision as well as
how the India-Asia collision may have modified global climate. Despite this
importance there are few established geologic constraints on this uplift history.
Here, we present stable isotope and major element analyses of paleosols
preserved in the Lower Miocene Liuqu Conglomerate as an indirect proxy for
India-Asia suture-zone paleoelevation and paleoclimate. Paleosol carbonate
nodules with average δ13C values of -9.4 ‰ indicate that soils forming at this
time were well vegetated by C3 plants. Major element weathering indices show
that these soils experienced significant collapse and loss of cations due to
weathering of similar intensity to that in the wet, low elevations of the modern
Himalayan foreland. Together, these results require that the Himalayan
orographic barrier, which blocks Indian Ocean moisture from entering Tibet
today, was not present or was much weaker during Liuqu deposition. This
suggests that the India-Asia suture zone as well as the modern Himalaya did not
attain their modern orographic configuration until as much as 40 ma after the
India-Asia collision was underway.
35
CONSTRAINING DRAINAGE EVOLUTION IN SOUTHERN TIBET; EVIDENCE
FOR A PRE-MIOCENE EXTERNALLY DRAINED RIVER SYSTEM NORTH OF
THE INDIA-ASIA SUTURE
Clay Campbell
Interpretation of remote sensing data, including high-resolution aerial imagery
and digital elevation models, suggests that a pre-Miocene river system may have
excavated reaches of the southern Tibetan Plateau as far north as the BangongNujiang suture. This river system, whose headwaters were located in the
presently internally drained region of the plateau north of the India-Asia suture,
flowed southwards across the Gangdese Shan and perhaps the Himalayan crest,
prior to the establishment of the current axial drainage system (Yarlung-TsangpoBrahmaputra and Indus rivers). Evidence of this paleo-river system manifests
itself throughout the Gangdese Shan and to a lesser extent across the Himalaya
in the form of N-S oriented wind gaps. Construction of regional river profiles
suggests a continuous N-S regional gradient from the Bangong-Nujiang suture to
the Indian foreland. The proposed paleo-river systems, which likely flowed across
this undisturbed regional gradient, would have been the primary mechanism
facilitating removal of sediment north of the present day drainage divide (the
Gangdese Shan). The Oligocene-Miocene Kailas formation, primarily deposited
between 26-24 Ma, contains lacustrine facies composed of organic material
along with amphibian and fish fossils, this suggests a much wetter pre-Miocene
climate and possibly upper plate extension. The late Oligocene-Early Miocene
Liuqu conglomerate, which was deposited along the southern margins of the
Gangdese Shan, is exposed along traces of our interpreted paleo-river system.
Imbricated sediments within the Liuqu conglomerate records initial N-S directed
sediment dispersal in a fluvial system followed by reversal during the Early
Miocene. The presence of paleosol interbeds with highly leached major element
chemical signatures indicates that these strata were deposited in a much wetter
paleo-environment, which is consistent with a subdued Himalayan orographic
barrier. We propose that renewed underthrusting of Indian lithosphere during the
early Miocene drove uplift of the southern Tibetan plateau and increased relief
along the Himalaya and Gangdese Shan, disturbing regional drainage patterns
and resulting in the establishment of the Yarlung-Tsangpo-Brahmaputra and
Indus rivers. This hypothesis is supported by a synchronous regional exhumation
signal along the track of the Indus-Yarlung river recorded by low temperature
thermochronometers at ~17 Ma.
36
GeoDaze Keynote Speaker
DATES AND DYNAMICS: SNOWBALL EARTH COMES OF AGE
Paul Hoffman
Snowball Earth is a theoretically well-defined climate state in which the entire
ocean and most continental areas are covered by dynamic glaciers, driven by
sublimation in the equatorial zone of the sea glacier. Ice albedo instability is the
trigger and deglaciation is self-induced, due to the steady rise of atmospheric
CO2 from normal volcanic outgassing in the absence of sinks for carbon on the
frozen planetary surface. Snowball Earth is invoked for two Cryogenian glacial
epochs when dynamic ice sheets are known from geological evidence to have
existed on all continents including low-latitude carbonate platforms. The snowball
hypothesis makes three sets of falsifiable predictions: (1) Cryogenian glacial
epochs were long-lived (millions to tens of millions of years), and both the onsets
and terminations were globally synchronous at low paleolatitudes; (2)
deglaciations occurred under extreme (105 ppmv) atmospheric CO2 radiative
forcing and consequent ocean acidification, and were followed by very high
surface temperatures and intense weathering; and (3) the biosphere was
irreversibly impacted. The first two prediction sets and arguably the third are now
strongly supported by observations unavailable when the hypothesis was
proposed. At the same time, climate models suggest that the snowball
atmosphere, cryosphere, ocean and lithosphere were more dynamic and
unstable than initially assumed, consistent with geological evidence. Many
aspects of the phenomenon are counterintuitive, meaning that insights from
modeling are essential to avoid testing false predictions. The ultimate cause of
Cryogenian refrigeration appears to have been basalt weathering following
emplacement of the 0.72-Ga Franklin large igneous province across
paleoequatorial (present Arctic) Laurentia during the breakup of supercontinent
Rodinia. Biomarkers tentatively imply a Cryogenian origin for multicellularity in
animals and for the dominance of green algae among eukaryotic primary
producers in Phanerozoic oceans.
37
EarthWeek Plenary Oral Session
MOUNTAINS AND TROPICAL CIRCULATION
Zach Naiman
Observed tropical convection exhibits zonal asymmetries that strongly influence
spatial precipitation patterns. The drivers of changes to this zonally-asymmetric
Walker circulation on decadal and longer timescales have been the focus of
significant recent research. Here we use two state-of-the-art earth system
models to explore the impact of earth’s mountains on the Walker circulation.
Changes to mountain heights can significantly influence the Walker circulation on
geologic time scales, and observed changes in tropical precipitation over millions
of years may be forced by changes in distant orography.
38
GeoDaze Poster Session
Economic Geology
RE-OS GEOCHRONOLOGY IN BLACK SHALES AND HEAVY OILS FROM
PETROLEUM BASINS IN THE COLOMBIAN ANDES
Sebastian Jimenez
The understanding of the geologic evolution of petroleum systems requires an
adequate comprehension of the organic matter deposition age, and further
events such as thermal maturation and hydrocarbons formation.
The Re-Os isotopic system in Black shales records the deposition time of the
organic matter. This attribute is the effect produced by anoxic conditions present
in the bottom of ocean basins that allow the precipitation of organic matter and
further sequestration of heavy metals -such as Re and Os- in the organic
compounds. The hydrogenous character of Re and Os enables a selective
leaching and precipitation of these metals sequestered only in the organic matter.
Therefore, if the reducing conditions have kept undisturbed until the present time,
the absolute depositional ages on black shales can be determined. In addition,
Os isotopic signatures record the isotopic composition of the ocean water at the
time of black shales deposit; these isotopic fingerprints provide a valuable tool for
tracing possible hydrocarbons source rocks.
Heavy crude oils have enough amounts of Re and Os that make them
susceptible to be dated by the 187Re-188Os isotopic system. Processes, such
as both hydrocarbon generation and migration, disturbed the Re-Os system
recording the time at which these events occurred.
The petroleum systems in the northern Andes present an excellent prospect to
evaluate the Re-Os geochronology in an active contractional orogen. In this
project, I present Re-Os information data from an intermontane petroleum basin
located in the topographic depression between the central and eastern
Cordilleras in the Colombian Andes
This work provides isotopic temporal constraints regarded to the evolution and
formation of hydrocarbons in basins related to thrust reactivation in a
compresssional regime.
39
Geophysics
RELATIONSHIP BETWEEN UPPER MANTLE HETEROGENEITY AND
CRUSTAL DEFORMATION IN THE NORTHERN APENNINES, ITALY
Angela Blanks-Bennett
The Apennine Orogenic belt in Italy is experiencing both crustal extension and
shortening in close proximity. It has been proposed that this unusual pairing of
deformation styles is related to a complex mantle convection system associated
with a sinking slab of Adria and the delamination of the micro plate mantle
lithosphere. To test this hypothesis, we evaluated crustal deformation models
assuming on a viscoelastic crust overlying a viscous mantle half space. Density
heterogeneities in the mantle is modeled using infinitely long cylinders of higher
or lower density than the ambient mantle. Model results suggest the shortening
along the northeast flank of the range is associated with sinking of negatively
buoyant mantle, whereas the extension in the southwest is connected to rising
buoyant mantle material. The model has implications also for observed crustal
thickness variations across the Northern Apennines, as well as the topographic
profile of the mountain chain.
https://gpi.central.edu
40
EVALUATING FAULT GEOMETRIES BENEATH THE NORTHERN
APENNINES, ITALY USING PRESENT-DAY SITE VELOCITIES MEASURED
BY GPS
Enrique Chon
Observed crustal structures of the northern Apennines, Italy have been explained
by a number of proposed geodynamic models of the tectonic setting, each with
different implications for present-day crustal kinematics. GPS geodesy shows
that the range is extending centrally and to the southwest, with simultaneous
shortening across the thrust belt to the northeast. This deformation has
happened in response to the northern Apennine block converging with the Adria
microplate to the northeast. The problem arises when the relative motions of the
plates are considered with respect to a stable Eurasia plate. Within this reference
frame, the combined area is expected to move together as it is bound to the
northeast by a seemingly static deformation front located beneath the Po Valley.
Past geodetic experiments have revealed that the Apennine block is actually
moving to the northeast at a faster rate than underthrusting Adria. This gives rise
to the question of whether subduction is ongoing beneath the Apennine thrust
belt, or if other geodynamic factors are driving this phenomenon. A likely fault
configuration has been proposed to accommodate the anomalous kinematic
behavior of the northern Apennines. The Apennines rests on top of two buried,
oppositely dipping faults. A moderately dipping normal fault trends from
southwest of the range to the northeast. A steeply dipping thrust fault lies
beneath the range front to the northeast and trends in a direction opposite to that
of the normal fault. In an effort to better understand the geometry and slip rates
of this fault system, we have chosen 32 continuous GPS stations to construct a
horizontal site velocity profile that runs across the range and parallel to the
direction of fault slip. The goal is to investigate the range of fault geometries and
slip rates that are consistent with the pattern of ongoing crustal deformation via
these site velocities. Our measurements will give insight to the non-uniqueness
of geometries, slip rates, locking depths, and other characteristics of the paired
fault system, which could help to further discriminate between proposed
geodynamic models.
41
A MODELING STUDY OF THE EFFECTS OF GEOMETRY AND CLIMATE ON
THE CIRCULATION AND DEPOSITION IN THE RED SEA
Hala Alwagdani
Using a terrain-following regional ocean model (ROMS) to carry out simulations
of the Red Sea, we will explore how plausible changes in geometry, climate, and
combinations thereof, may have affected circulation and deposition in the past
relative to today. From a geological perspective, the Red Sea first formed during
the Eocene and continues to widen as the Arabian Plate moves to the northeast.
From the climate perspective, the Red Sea is located in the transition zone
between the tropical easterly wind belt and the mid-latitude westerlies, and is
subject to significant seasonal variability due to its proximity to the Indian
Monsoon region. Analyses of the circulation and deposition in simulations with
modern bathymetry, a paleobathymetry and shifted wind-regimes will be
discussed and compared.
42
LOI DATA FOR TOTAL ORGANIC AND TOTAL INORGANIC CARBON IN THE
NORTH AWASH OSI ISI SITE IN NORTHERN ETHIOPIA AND ITS
IMPLICATIONS ON PAST ENVIRONMENTAL AND CLIMATE CONDITIONS
DURING HOMINID EVOLUTION
Joseph Valachovic
The Hominin Sites and Paleolakes Drilling Project (HSPDP) is a collaboration of
different universities and research centers whose goal is to collect drill cores from
ancient lake beds in an attempt to improve our understanding of the local
paleoclimate and environmental impacts on hominid origins in Africa during the
late Pliocene and early Pleistocene. The 187m core used in this study (HSPDPNAO14-1B) was collected from the North Awash Osi Isi site, encompassing the
late Plicoene (~3.4-2.94Ma) Hadar formation in northern Ethiopia, where many
early hominids have been found in previous nearby excavations. Methods of
extracting information from these cores has involved many different techniques.
We studied the total organic carbon (TOC) and inorganic carbon content (TIC)
content of the cores utilizing the Loss on Ignition method in lacustrine deposits.
This data, in combination with lithostratigraphic and geophysical log data provide
critical information about the environmental conditions of these lake margins over
the cored interval of time. Cores were sampled every 32cm in multiple sections.
They were then plotted against other data sets to see where peaks matched and
correlation is established.
Peak levels in TIC in this core correlate with sections of the core with large
carbonate nodules and coarser light colored grains with a lack of organic material
in the section of the core. Low TIC values are associated with mostly massive
beds of brown siltstones, which typically are correlated with TOC peaks. TOC
peaks are associated with massive brown silty clays, with occasional smaller
carbonate nodules. Low TOC values are associated with sediments that are
lighter in color and had larger carbonate nodules. TOC in the upper 35m of the
core analyzed to date are surprisingly high given their mostly brown silty
lithology. Lithologies in the upper ~35m of the core suggest fairly shallow lake
margin conditions, with the more red-brown silty clays and carbonate nodule-rich
intervals indicating paleosol alteration. Green mudstones and core log data
indicate a deeper lacustrine phase in the lower portion of the core yet to be
analyzed.
43
DECOMPOSITION OF THE ATLANTIC MERIDIONAL OVERTURNING
CIRCULATION INTO ITS MAJOR COMPONENT TRANSPORTS IN CMIP5
MODELS
Rebecca L. Beadling
The Atlantic Meridional Overturning Circulation (AMOC) plays an important role
in Earth’s climate system as it transports significant amounts of seawater, heat,
nutrients and salt from the tropics to the high northern latitudes. This circulation
drives up to 1.3 petawatts of heat northward in the Atlantic, significantly
contributing to the climate in the North Atlantic region. Since 2004, direct and
continuous observations of AMOC have become available with the launch of the
RAPID transatlantic array at 26.5 ° N, significantly advancing our knowledge and
providing a benchmark for comparison of climate model simulations.
Observations from this array reveal that the AMOC has been declining in
strength, mostly attributed the increased southward return flow of the subtropical
gyre and decreased southward flow of lower North Atlantic Deep Water (NADW).
According to the Coupled Model Intercomparison Project Phase 5 results, the
AMOC is projected to decline under future warming scenarios. Our study aims to
determine the mechanism of future AMOC decline in each CMIP5 model by
decomposing the circulation into the Gulf Stream, Upper Mid-Ocean (UMO), wind
driven Ekman, Upper and Lower NADW and Antarctic Bottom Water (AABW)
Transports at 27 ° N. We will compare the model simulated results with RAPID
observations to gain a deeper understanding of future AMOC behavior in climate
model simulations.
44
LINKING CLIMATE VARIABILITY AND CORAL HEALTH THROUGH GREAT
BARRIER REEF CORAL RECORDS
Emma Reed
The ocean north of Australia is an engine for regional and global climate. Sea
surface temperatures here drive the Australasian monsoon and influence the El
Niño-Southern Oscillation (ENSO). Corals in this region respond to stresses,
including warming and ocean acidification, that are intensifying with current
climate trends. Understanding coral response to past stressors can help predict
how reefs will respond to current climate change. Coral paleoclimate records
offer a way to fill this knowledge gap.
This research focuses on coral cores from three sites in the northern Great
Barrier Reef (Eel Reef, Portland Roads, and 13-050) that form a transect that
reflects changes from nearshore to offshore environments. Coral records from
these sites include three proxy approaches:
1)
2)
3)
Geochemical methods (δ18O, δ13C, and Sr/Ca), which reflect seawater
temperature and salinity
Growth banding (coral extension rate, density, and calcification rate),
which record changes in coral growth in response to environmental factors
(e.g. temperature, salinity, and pH)
Luminescence banding, which measures organic matter incorporated into
corals during large precipitation events
Preliminary results confirm that coral geochemistry tracks seasonal change in
climate, including temperature and precipitation, that vary with ENSO and
monsoon events. Furthermore, between 1979 and 1989, coral calcification was
highest during years with cool summers. This result aligns with other studies,
which suggest that Great Barrier Reef coral growth has slowed after passing a
threshold in temperature and pH. Furthermore, high coral growth rates in this
region may allow us to resolve extension rate on sub-annual time scales, which
can yield better Sr/Ca temperature reconstructions, as well as track the response
of coral growth to annual temperature extremes. Ongoing data collection,
including field work in Australia, will elaborate on these findings. Such work can
prove valuable not only to paleoclimatologists, but to Great Barrier Reef
researchers as well.
45
TRACE ELEMENT ANALYSES OF SPELEOTHEMS AS INDICATORS FOR
DROUGHT IN SOUTHWEST U.S. CAVES
Melissa Harrington
Understanding the character of drought on both long (millennial) and short
(seasonal) timescales is critical for water resource management, especially in the
Southwest where water is scarce. Trace element analyses of speleothems are
emerging as a new method for reconstructing past drought in semiarid regions.
Previous work in semiarid areas such as southern Australia indicates that certain
trace elements record paleohydrologic changes over time. Here we present
preliminary results from trace element concentrations analyzed via laser ablation
ICP-MS in a ~3500-year-old stalagmite from Fort Huachuca Cave in southern
Arizona. The concentrations of Sr, Ba, P, Y, and U vary according to the annual
cycle. Sr and Ba covary strongly, while P, Y, and U covary inversely to Sr and Ba
cycles. We hypothesize that Ba and Sr concentrations are higher in arid
conditions, whereas high concentrations of P, U, and Y correspond to wet
conditions. Comparison of cave drip water elemental data with instrumental
precipitation records will help determine which elements in speleothems can be
used as a proxy for rainfall. This work is the first step in developing a new aridity
index based on multi-elemental analysis of speleothems.
46
ANALYSIS OF AMAZON RAINFALL DATA SETS AND THE IMPORTANCE OF
PALEOCLIMATE RECORDS
Anson H. Cheung
Global climate change is influencing the whole world. The IPCC AR5 projects the
Amazon region’s climate drier in the future. Meanwhile, recent drought events
(2005, 2010) were unexpected and had severe impacts on fire and carbon
balance. While precipitation affects the carbon balance, the precipitation
variability in the Amazon region is not well known. Station and satellite data are
available and can be used to better understand such variability. However,
Precipitation in the Amazon region has been previously shown to be highly
spatial heterogeneous. Additionally, reanalysis on different data sets show that
spectral and spatial discrepancies exist between different data sets. Further,
these data only extend back to the early 1900s. Hence, the availability of
paleoclimate records is important to help us validate these data sets and extend
the rainfall record. To better understand the spatial extent of paleoclimate
records, we used station data as an analogue to elucidate climate in the Amazon.
47
DETRITAL ZIRCON ANALYSIS OF ROCK SLABS FROM BRAZIL FOR
PROVENANCE, ABSOLUTE AGE AND REGIONAL GEOHISTORY STUDY
Jessie McGraw
The purpose of this study is for a group of undergraduate students to determine
the ages of a variety of rock samples using Detrital Zircon analysis. Using the
UofA Laserchron lab, the students are going to conduct an age and provenance
study and interpret the data to construct a geologic history of the region of Brazil
from which the slabs were removed. The zircon crystals were separated from the
rocks first by crushing the original samples of rock that contained the crystals,
then using a magnetic separator to remove all of the magnetic minerals, thirdly
with mineral separation to separate the minerals by their densities in heavy
liquids, leaving mainly pure zircon crystals to be used in the sample. The
samples were then mounted for Uranium-Lead analysis and then run through
SEM and CL imaging to provide images of the internal structure of the crystals.
Finally the samples were analyzed with laser ablation mass spectrometry to
determine their absolute age, and based on the half-life of those isotopes, yields
an absolute age of the formation of the zircon crystals. This data will be
interpreted to infer the provenance of the different rock types. Students will then
use existing geologic maps and the known information about these rocks to
construct the geologic history of the region based on the data gathered from the
zircon analysis. The results of this research will provide insight into the geologic
history of this area of Brazil.
48
GEOCHEMICAL ANALYSIS OF MELT GENERATION IN MAINE MIGMATITES
Daniel Favorito
Migmatites are rocks that represent the first occurrence of crustal anatexis in
orogenic events and preserve characteristics of both their metamorphic
precursors and the products of their melting. The presence of migmatites has
important implications for how mountains and the continental crust are created
during orogenies. However, many questions concerning these processes are not
fully understood, including the actual mechanism for heating such rocks and the
nature of the geochemistry of the first stages of anatexis. The geochemistry is
particularly problematic because the leucosome that represents the “molten”
portion of the migmatite may have been subjected to fractional crystallization and
re-crystallization processes. As a result, bulk rock studies of migmatites may not
necessarily indicate what is happening over the course of melting from beginning
to end. This study aims at addressing this question by conducting geochemical
microanalysis of a group of migmatites collected from the Tumbledown and Weld
Anatectic Domains, Maine.
Bulk rock geochemistry of samples of migmatites from Maine has been
determined by previous authors, but new microanalytical data are generated in
this study to compare and constrain the results of melting models. Thin sections
were made in order to study the petrography of the samples and subsequent
electron microprobe analysis (EPMA) was conducted in order to determine the
chemical composition of garnet within the samples and examine chemical
zonation of crystals. Garnet cores are enriched in iron and yet depleted in
manganese, whereas other major elements were relatively consistent throughout
chemical transects. These significant changes in the garnet composition indicate
the presence of partial melting, with the cores of the garnet representing
metamorphic growth; in contrast, the rims representing magmatic growth. Trace
elements such as yttrium did not diffusively equilibrate compared to the
abundances of major elements, indicating that the metamorphic event which
resulted in migmatization was likely short lived.
49
PALEOENVIRONMENTS AND AGE ANALYSIS OF THE LOBO FORMATION: A
LARAMIDE SYNTECTONIC DEPOSIT IN SOUTHERN NEW MEXICO
Marie G. De los Santos
The purpose of this study is to improve our understanding of the Lobo
Formation’s age and environments of deposition during Laramide tectonism in
the southern Rockies.
Three sections of the Lobo were measured. Two sections are near Capitol Dome
in the Florida Mountains: Capitol Dome-M is ~116m thick and Capitol Dome-A is
~200m thick. Both sections consist of intermontane lacustrine or palustrine,
fluvial, and alluvial-fan deposits and are a fill of an intra-uplift basin following
extensive Laramide faulting that exhumed basement outcrops. Capitol Dome-M
contains a progradational succession of wet to arid conditions as recorded by a
sequence of very fine to fine-grained sandstone, reddish-brown siltstone and
pebbly sandstone, and an upper cobble and boulder conglomerate with
basement clasts. Capitol Dome-A contains several paleosols with nodular
carbonate horizons near the base and a contrasting upper section of cemented
sandstones, pebble and boulder conglomerates with Paleozoic limestone and
basement clasts, and non-carbonate paleosol horizons.
The third section of the Lobo in the Victorio Mountains is an upward-fining
succession (~325m thick) composed of alluvial-fan and fluvial deposits. Basal
conglomerate clasts were derived from diverse sources: a Proterozoic basement,
Paleozoic carbonate and siliciclastic strata, Jurassic basalt flows, and Lower
Cretaceous strata (Bisbee Basin). The overall depositional style and presence of
paleosols indicate Lobo deposition in arid environments with a modest
depositional rate of ~0.02mm/a.
Paleomagnetic analysis of the Capitol Dome-M section indicates four brief
normal intervals amongst a mostly reversed section. Our data suggest deposition
occurred between 59 and 53Ma (Paleocene-Eocene) followed by a postdepositional clockwise rotation of ~25-30° about a vertical axis. Paleomagnetic
data from the Victorio Mountains section indicate no post-depositional rotation.
Detrital zircon data from the Victorio Mountains section shows the youngest
zircons dated at ~66Myr (+-3); however, a majority of the ages is ~1.4Ga
suggesting only minor variations in sediment sources. Detrital zircon data from
the Capitol Dome-A section shows a main peak at 1-1.2 Ga and several minor
peaks at 1.4, 1.7, 2.7 and 0.4Ga suggesting various sediment sources, including
the recycling of Bisbee Group strata. One Cenozoic grain from the middle of the
section is dated at 57.5Myr (+-1.2), which correlates well with our suggested
paleomagnetic age.
50
LU-HF ISOTOPIC TRENDS DURING SHALLOW SUBDUCTION AND
FOUNDERING OF THE FARALLON SLAB AND THE RESULTANT MAGMATIC
SWEEP ACROSS THE SOUTHWESTERN U.S.
Michelle Dafov
Previous research on Samarium-Neodymium (Sm-Nd) isotopic ratios of granitic
bodies emplaced during the shallow-subduction and then roll-back or foundering
of the Farallon slab in the Late Cretaceous to Middle Miocene in the
Southwestern United States shows similar radiometric signatures to the
basement terranes upon which the plutons were intruded regardless of the
tectonic configuration at the time (Farmer and Depaolo, 1984). This trend,
however, is not well-established in the Lutetium-Hafnium (Lu-Hf) isotopic
system. The two radiometric systems are similar, however, changes in εHf
isotopic values have been used in other orogenic systems (e.g. Tibet) to infer
changes in tectonic environment. Is it possible that εHf values in the U.S.
Cordillera will exhibit trends related to the tectonic setting? Conversely, if the εHf
trends reflect only basement terrane composition, then do the data from other
orogens need to be reevaluated? We have collected granitic samples from
around Arizona, New Mexico, and West Texas and will process and analyze
them at the Arizona Laserchron Lab to help resolve the usefulness of the Lu-Hf
isotopic system in understanding orogenic processes.
51
BRITISH COLUMBIA COAST MOUNTAINS METASEDIMENTARY ROCKS:
AGE CONSTRAINTS AND PROVENANCE
Michelle Dafov
The history of the Coast Mountains of British Columbia has long been a
complicated one to piece together. This project focuses specifically on the ages
and tectonic connections of the belt of metasedimentary rocks in the Coast
Mountains that were intruded by batholiths during a time of subduction. This will
provide a history of the growth of North America as each terrane has been added
to the continent and will put constraints on the boundaries of these terranes.
There are four arc-type terranes that are being studied; Yukon-Tanana,
Alexander, Stikine and Wrangellia. Four samples have been collected from
Lochborough and Bute inlets, British Columbia, and this coming summer, more
samples will be collected from Knight inlet. One sample from Lochborough Inlet
has been processed in the Arizona Laserchron Center for U-Th-Pb ages using
the Element2 and Nu mass spectrometers, maximum depositional age and
provenance have been determined. Our goal is to see whether Precambrian
ages are present in the metasedimentary samples from Bute and Knight inlet,
which would suggest they belong to the Yukon-Tanana terrane. There is reason
to believe these sediments originate from Yukon-Tanana due to their quartz-rich
composition. Field observations of the samples from Bute inlet show slightly
metamorphosed quartz-rich turbidites, common of Yukon-Tanana terrane. If ages
are Precambrian, new boundaries will be made for Yukon-Tanana that extend
much farther south than previously thought. The Wrangellia terrane is
Pennsylvanian in age and has granite intruded that is 180-150 Ma. The sample
that has been dated has a cluster of ages from ~268-319 Ma and a cluster at
~150-167 Ma. Those ages show a clear signature of Wrangellia terrane, which
would mean the boundary of Wrangellia extends further inboard than previously
recognized. After more samples are analyzed, we hope to see whether ages of
metasedimentary rocks from Bute inlet showing ages are Precambrian, indicating
Yukon-Tanana derived sedimentary rock.
52
JACK HILLS QUARTZITE YIELDS HADEAN AGE ZIRCONS
Michelle Dafov
Until recently, the most we knew about early Earth, during the Hadean eon, is
that it was a hellish world absent of a hydrosphere that operated with different
processes from today’s Earth. However, zircons within the Jack Hills Greenstone
belt in Western Australia have been dated back to 4.38 billion years old
(Harrison, 2009) and tell a different story. This poster covers the process of
extracting zircons and conducting Uranium-lead analysis- done by students in the
Geos 251 class at the University of Arizona. Initially, the quartzite sample was
crushed and then sieved in order to collect grains 425 microns in size or less.
Low density material was then removed by panning, and the rest of the material
was run through a magnetic separator to remove the magnetics. The remaining
sediment was poured into methyl iodide, which is a heavy liquid that allows for
separation of the dense zircons from the lighter material. The zircons were then
mounted and imaged with a scanning electron microscope to bring out zonation
within the crystals. After running the samples through the Element2 mass
spectrometer for U-Pb analysis, results showed a variety of ages. There was a
small cluster at 3.07 Ga, a large cluster at 3.3-3.7 Ga with peaks at 3389, 3462,
and 3597 Ma, and most importantly a cluster at 3.85-4.15 Ga with a peak at 4019
Ma. Ages generated for standard zircons were within 1% standard error of their
known ages which gives us confidence that the ages of the unknown zircons
were also within 1% accuracy. The Concordia graph also shows accuracy of our
results, as most ages sit on top of the Concordia line. Considering the oldest rock
known on Earth is 3.9 Ga, the only information known about what was happening
on Earth before then comes from Hadean eon zircon grains. Hadean zircons
from Jack Hills likely crystallized in conditions below 700 °C (Harrison, 2009),
indicating Jack Hills zircons likely came from felsic rocks. We can therefore infer
from our results of >4.1 Ga zircon ages that there must have been felsic crust
formation earlier than 4 Ga in order for these zircons to have formed. In other
words, current geologic processes may also have been occurring during the
Hadean eon. This research experience allowed undergraduate students to be
exposed to sophisticated equipment and techniques required to extract and
analyze zircons, providing them with useful skills for their futures in geology.
53
TONALITIC MAGMATISM, EXHUMATION, AND ROTATION ALONG THE
BAKER-OLDS FERRY TERRANE BOUNDARY, BLUE MOUNTAINS, EASTERN
OREGON
Alexandra S. Macho
A series of four tonalitic plutons intrude on or near the Baker-Olds Ferry terrane
boundary in the Blue Mountains of eastern Oregon. This study utilizes multiple
geochronologic techniques in order to help constrain the geological history of the
Blue Mountains within the footprint of the IDOR EarthScope project. These
plutons have been inferred to be similar in both composition and age to plutons
affected by the Salmon River suture zone along the arc-continent boundary; here
we explore the different exhumation history recorded in these two areas.
CA-ID-TIMS U-Pb zircon dating reveals a younging trend of pluton emplacement
from SW to NE: Tureman Ranch (129.36 ± 0.055 Ma), Amelia (125.50 ± 0.076
Ma), Pedro Mountain (124.84 ± 0.073 Ma), and Lookout Mountain (123.84 ±
0.042 Ma). Geochemical analyses indicate that the plutons were sourced from
mantle-derived and crustal melts of the juvenile accreted arc terranes.
Hornblende thermobarometry data are consistent with relatively shallow (< 3
kbar) emplacement depths. Ongoing thermochronological studies (40Ar/39Ar on
hornblende and biotite and (U-Th)/He on zircon) provide timing constraints on the
exhumation of these plutons relative to similarly aged plutons associated with the
Salmon River suture zone. Preliminary paleomagnetic results from two of these
plutons indicate that the whole boundary may have undergone significant vertical
axis rotation since ~120 Ma. Overall, the age of plutonism in eastern Oregon is
coeval with high-grade metamorphism and plutonism in the Salmon River suture
zone, although the subsequent history appears to differ from adjacent cratonic
North America.
54
UTILIZING ArcGIS FOR DATA INTEGRATION AND RECONSTRUCTION OF
HISTORICAL GEOLOGIC MAPS: A CASE STUDY OF THE COAST
MOUNTAINS BATHOLITH IN BRITISH COLUMBIA, CANADA
Intan Yokelson
Historical geologic maps, that are still being used today, were primarily based on
field investigation techniques that were developed over the last century. As our
understanding of tectonics and other geologic processes has grown over the past
several decades, new technologies have allowed us to better integrate analytical
data thereby requiring a fresh look at these historical geologic maps.
As my thesis project for my certificate in geographic information systems, I am
utilizing my field area and re-examining the geologic maps of the Coast
Mountains batholith (CMB) in British Columbia. This region has proven to be
challenging for two main reasons 1) access to the area and 2) a complicated
compositional evolution history. The historically known geologic units in this
region were characterized during a time before the theory of plate tectonics was
a main driving force in our geologic understanding of the Earth processes.
Additionally, rock classifications from that time are unusual and out of date for
modern classification schemes, thereby making this region ideal for this type of
study.
This study will utilize the current pluton boundaries from the old maps while 1)
update the rock classifications 2) check the geologic extent in the field and with
the help of Google Earth, and 3) digitize and integrate the geochronological and
geochemical data sets as independent layers; allowing for a better to
understanding of the history of magmatic emplacement in the CMB. The summer
of 2014 was spent mapping CMB pluton outcrops and sample collection for U-Pb
geochronology as well as Lu-Hf and whole rock geochemistry. The major areas
of investigation were along the shoreline of Bute Inlet and in the Waddington
Range in order to determine major pluton bodies across the region.
55
DETRITAL ZIRCON AGE ANALYSIS OF THE JACK HILLS QUARTZITE
CONGLOMERATE (RED)
Jessie McCraw
The purpose of this study is for honors students in Geos 251 at the UofA to
analyze the detrital zircons found in the Jack Hills Quartzite of Western Australia
to provide data to identify information about the surface of Earth during the
Hadean Era. This study sought to address the processes that formed and
shaped the Earth’s continental geosphere based on interpretations of the age
data yielded by the zircon crystals. In this study, the ages yielded by the zircons
support the idea that the earth’s surface was being formed and shaped by
weathering and erosional processes, similar to those in occurrence today,
because detrital zircons are of igneous origin the crystals must have been
transported from their source, perhaps via water. The zircons were extracted and
separated from the quartzite first by crushing the original quartzite sample, then
using magnetic separation to remove all magnetic minerals in the mixture, thirdly
with mineral separation to separate the minerals by density, leaving mostly pure
zircon crystals to be used in the sample. This sample was then mounted and
examined with SEM and CL imaging to give students an idea of the internal
structure of the crystal. Finally the sample was analyzed by laser ablated mass
spectrometry to determine their absolute age via the decay of uranium isotopes
to lead, and based on the half-life of these isotopes, yielding an absolute age of
the formation of the zircon crystals. The samples analyzed by the UofA students
yielded a maximum age 4.2 Ga, implying the presence of felsic igneous rocks in
the geosphere at that time. Significant age peaks in this sample were the
youngest zircons at 3.066 Ga, implying that the age of deposition must be
younger than 3.006 Ga, the largest concentration of crystals near 3.382 Ga
showing that the igneous contributor to the quartzite depositional environment
was mostly material this age, and the highest age of 4.2 Ga.These zircon crystals
are the oldest known record of geologic processes occurring during the first 500
Ma of Earth history, because the oldest terrestrial rocks are only 3.96 Ga. The
analysis of this sample of the Jack Hills Quartzite gives support to the idea of a
possible hydrosphere as early as 4.4 billion years ago, which ultimately has
implications about the origin story of the earliest life forms on Earth, opening up a
new field of interest for future researchers.
56
CLIMATE AND TECTONIC CONTROL ON EROSION ACROSS THE ALPINE
FAULT, SOUTH ISLAND, NEW ZEALAND
Kaitlynn Walker
In the South Island of New Zealand, both tectonics and climate influence the rate
of erosion. The Alpine Fault is a transpressional fault, crossing the South Island
of New Zealand through the Southern Alps Mountains along the AustralianPacific plate boundary. The Alpine Fault creates a drainage divide with
catchments to the east and west of the fault. To the west of the Alpine Fault an
extremely wet climate with high rates of physical erosion and uplift exist, while
the east is characterized by a drier climate with significantly lower rates of
physical erosion and uplift Four river sand samples were collected in various
locations: three of the samples were collected west of the Alpine fault and one
sample was collected east of the fault. Two samples (NZ2 and NZ3) are located
in the same catchment. The sizes of the catchments vary from sample to sample.
By analyzing the U-Pb ages of zircons in each sample, the source rocks of the
samples can be determined. I also hope to evaluate the effect of a big catchment
versus a small catchment. and contain very similar ages. Most of the U-Pb zircon
ages of these samples range from Cenozoic to Cretaceous. Zircon fission track
analysis will be conducted on the four samples in the future. This will evaluate
the respective role of climate and tectonics on erosion across the Alpine Fault of
the Southern Alps of New Zealand. If the thermochronological ages of the
samples west of the Alpine Fault are older then it will be concluded that climate
has a greater effect on erosion in the South Island of New Zealand. By
understanding the erosional controls of the region, this study will provide insight
on the respective roles of between climate and tectonics on orogenic evolution.
57
(U-TH)/HE AND U-PB THERMOCHRONOMETRY AND U-PB
GEOCHRONOMETRY OF EXPOSED BEDROCK OUTCROPS IN THE
WINDMILL ISLANDS, ANTARCTICA
Patrick Boyd
With 98% of Antarctica covered in ice sheets it is the least explored continent on
earth. The Windmill Islands in East Antarctica are part of the 2% of Antarctica
that isn’t encapsulated by ice, and the only such outcrop for hundreds of miles in
any direction. Valuable inferences can be made about the Windmill Islands and
the surrounding Wilkes Land regions history through analysis on the exposed
bedrock. High and low temperature apatite thermochronometers (U-Th)/He and
U-Pb and U-Pb zircon geochronometry can give us a constrained thermal history
of exposed bedrock outcrops in the Windmill Islands, Antarctica. By performing
chronometry techniques on multiple granites, gneisses, and diorites from the
areas bedrock, inferences can be made regarding the crystallization and cooling
history of the coast of this area of Wilkes Land, East Antarctica. Crystallization
ages seen in U-Pb zircon data will allow us to view the last major thermal event
in the area, while high and low temperature thermochronometry data will allow us
to know the timing of metamorphic events in the region as well as the erosional
history in the Windmill Islands. This data will make it possible to better
understand the tectonic history of the Windmill Islands and surrounding Wilkes
Land region, and will ultimately lead to a more complete picture of the role
eastern Antarctica has played in earth’s tectonic history.
58
FORELAND BASIN STRATIGRAPHIC CONTROL ON THRUST BELT
EVOLUTION
James B. Chapman
The linkage between orogenic activity and foreland basin stratigraphy is well
established; however, potential controls by foreland basin stratigraphy on thrust
belt architecture have not been fully evaluated. Mechanical properties of typical
foreland basin stratigraphic successions influence the structural development of
fold-thrust belts in predictable ways. Fundamental features of foreland basins
include the onset of rapid subsidence and deposition of a coarsening-upward
sedimentary succession. In the lower part of this succession are fine-grained
back-bulge and distal foredeep deposits. Enlargement of the orogenic wedge
through frontal accretion incorporates the foreland basin strata into the thrust belt
and early foreland basin depositional units may be systemically exploited as a
thrust detachment zone, often culminating in multiple detachment levels. We
suggest that foreland basin stratigraphic architecture has significant influence on
the structural development of thrust belts and that, by extension, processes that
influence foreland basin sedimentation may ultimately influence orogenic
evolution far removed in time and space.
59
ATTEMPT TO CONSTRAIN INITIATION OF THE SOUTHERN TIBETAN
DETACHMENT SYSTEM USING U-PB GEOCHRONOLOGY AND TEMPORAL
EVOLUTION OF ASSOCIATED INTRUSIONS
Stephen Sobansky
The Southern Tibetan Detachment System (STDS) marks a top to the North low
angle detachment fault that occurred when gravitational potential energy
exceeded the forces created by the collision of the Indian and Asian plates. The
STDS consists of Tethyan metasediments and syn-orogenic detritus in the
hanging wall to the North, and orthogneisses of the Greater Himalayan
Sequence (GHS) in the footwall to the South. Samples were collected along the
footwall from three undeformed leucogranite sills and one mylonitized
leucogranite sill. Zircon cores are to be analyzed with U-Pb radiometric dating
techniques are expected to yield ages >500 Ma, while the metamorphic rims of
zircons found in these sills are expected to yield ages ranging from 17-9 Ma. The
ages of the rims will likely correlate to the onset of decompression melting, which
occurred synchronously with initiation of the STDS and subsequent exhumation
of GHS metamorphic rocks and Tethyan metasediments. We propose that as
exhumation occurred along the STDS, gneissic rocks straddling the brittle ductile
transition zone (12-15km depth & 3.5-4.5 kb) and overlying Tethyan
metasediments experienced jointing as they were exhumed toward the surface
via listric faulting. As jointing occurred, pressurized, highly evolved felsic magma
penetrated the fractures in the form of leucogranite dikes and sills. The study’s
final intention is to compare the rim ages from the three undeformed leucogranite
sills with the individual mylonitized sill in an attempt to better understand the
temporal evolution of intrusions along joints within our study area.
60
PROVENANCE OF EO-OLIGOCENE AND QUATERNARY STRATA IN THE
LOESS PLATEAU THROUGH COMPARATIVE STATISTICAL
Jordan Abell
Characterizing provenance of the Quaternary eolian dust deposits of the Chinese
Loess Plateau provides a means to better understand the aridification history of
central Asian basins and local to regional wind patterns during the onset and
amplification of Northern Hemisphere glacial cycles over the past ~2.6 Ma. The
Chinese Loess Plateau is composed of interbedded loess and paleosol beds.
This research aims to understand the provenance of the Chinese Loess Plateau
by charactering the detrital zircon U-Pb age distributions on Loess Plateau
samples and potential source areas for the loess-paleosol strata. Our research
compiled previously published zircon U-Pb age data (n> 35000) from the
literature along with new age zircon U-Pb age data (n> 3000) from modern dune,
loess, and yardang samples. In addition to investigating provenance of the
Quaternary Chinese Loess Plateau deposits, we also apply this dataset to
understanding the Eo-Oligocene age eolian and eolian-influenced rock from (SE)
Asia. To the latter, these deposits provide information on wind orientations during
a critical phase of surface uplift of the Himalayan-Tibetan orogen and
intensification of the Indian monsoon. Most previous studies argue that most of
the Quaternary Loess Plateau strata were sourced from the proximal Gobi Desert
and adjacent sand deserts to the northwest of the Loess Plateau (e.g., Mu Us,
Gobi). However, the observations made in this study are not consistent with this
hypothesis. The relative proportion of zircon crystals from the loess deposits in
the age ranges of 350–450 Ma and 475–525 Ma suggest that sediment was
drawn from a wider geographical area than the Gobi Desert and adjacent sand
deserts. These data indicate that the source regions are not that far north, but
rather include the Northern Tibetan Plateau (NTP) and in the area due west of
the Loess Plateau (e.g., Qaidam Basin). Because this observation does not fit
the modern observation of surface and mid-upper level atmospheric circulation,
we contend that this marks a major reorganization of atmospheric circulation over
central Asia during glacial periods when more dust was deposited on the
Chinese Loess Plateau.
61
Planetary Science
WIND EROSION LANDFORMS ON MARS
Cyanna Hicks
Wind erosion on Mars is thought to be similar to the process of wind erosion on
Earth, but how the two planets relate in terms of these processes is not readily
known. This project seeks to find similar landforms on both Mars and Earth that
were created by erosion, and compare and contrast them. These features
include yardangs, wind scours, sand dunes, and lineated terrains. One of the
most studied features in this project is wind eroded mesas, which are thought to
be the features that form yardangs on both Earth and Mars. This study is done
using Google Mars and Google Earth imagery, as well as other remote sensing
data from sources such as HiRise.
The main findings of this project are that most landforms on Mars can be much
larger, up to ten times larger, than their counterparts on Earth. The reasons for
this could be that gravity is much less strong on Mars than it is on Earth, causing
particles to more easily taken up by the wind. Also, there is very little water
erosion on Mars due to the containment of most of Mars's water in the poles of
Mars. This makes it easier to see the wind erosion. The specific landforms found
on Mars that match those on Earth include those listed above, as well as
katabatic wind patterns that are seen above mountains and craters on Mars.
From this project, a map will be made that includes possible current and ancient
wind patterns using the wind erosion features found. This map can indicate how
wind patterns have changed over the course of Mars's history and possibly offer
insight into the evolution of Mars's atmosphere.
62
EOLIAN AND GEOLOGIC MAPPING NEAR GORDII DORSUM OF THE LARGE
FOSSAE FORMATION OF MARS
Allison McGraw
There are many locations on Mars where the surface material is of an unknown
composition. Thermal inertia values of 60 – 100 [J*m^-2*K^-1*sec^-1/2] suggest
fine-grained sand but it is likely that there are large quantities of ash material
from ancient Mars volcanic eruptions. This area, (2.8 degrees N, 214 degrees E),
is southwest of Gordii Dorsum in the Large Fossae Formation is due west of the
Tharsis volcanic region, which could have been a source of fine ash material that
could be present in the dune field in this area. Mapping in the thermal IR and
closer investigations of thermal inertia values may not be enough information to
determine the composition, although those aspects are also investigated here.
Other processes near the surrounding area of interest could aid in understanding
the composition of the material such as eolian processes and geologic contacts.
Wind direction and eolian processes in the area southwest of the Gordii Dorsum
dune field will be examined from satellite images; these images will be highly
investigated in the red wavelength of light. Potential geologic contacts could be
mapped in this region as well with images taken in STEREO. The HiRISE
satellite orbiter takes the highest resolution images of Mars; this high resolution
may be enough to map this area of interest in the Large Fossae Formation to
interpret surface material and surface processes present.
63
Environmental Science
OVER THREE YEARS OF MONITORING 129I SPREAD IN PACIFIC OCEAN
AFTER THE 2011 FUKUSHIMA DAIICHI NUCLEAR POWER PLANT
ACCIDENT
Ching-Chih Chang
129I is a long-lived radionuclide that has been used as a useful environmental
tracer. At present, the global 129I in surface water is about 1-2 orders of
magnitude higher than pre-1990 levels. The anthropogenic 129I signal produced
from industrial nuclear fuel reprocessing plants is known to be the primary source
of 129I in marine surface waters of the Atlantic, and elevated 129I values are
found globally.
The Great East Japan Earthquake and the induced tsunami in 2011 triggered the
nuclear shutdowns, failures, and partial meltdowns of Fukushima Daiichi Nuclear
Power Plant. The accident resulted in a series of radioactive material releases
into the environment and spread out through atmospheric and ocean circulation.
We will present 129I results of water samples collected weekly near Scripps
Institution of Oceanography, San Diego, CA for the past 3 years. We also have
several measurements collected a year apart from Kaohsiung, Taiwan, which
represent west margin of Pacific Ocean, and from Alaska, Washington, and
Oregon. By establishing 129I time series, we can observe the spread of 129I in
the surface waters of the Pacific Ocean that resulted from the accidental
releases.
64
ADVENTURE SCIENCE: EXPLORING ROCK WEATHERING AT THE COLD
BOUNDARY OF EARTH
Kexin Li
Soil is a limited natural resource generated during slow weathering processes,
where microbes, plant roots and water interact with rock and releases nutrients.
Ignition of carbon and nutrient cycle at places where life meets rock is therefore
the main driver of soil formation and ecosystem development. Compared with
lower altitudes, mountain and Polar regions normally undergo a more energetic
weathering process dictated mainly by physical and chemical forces. During this
process chemical components of rock (major minerals) are transformed into
secondary phases and nutrients translocate to rock surfaces where they support
the life system.
A total of 13 sampling campaigns were conducted at following locations: Franz
Joseph Land (Russian arctic), Dry Valleys (Antarctica), Mt Denali & Mt. Witney
(Alaska and continental USA respectively), Zero de Plomo (Chile), Weisshorn
(Switzerland), Mt. Kilimanjaro (Kenya), Pamir Mt. (Tajikistan), and Himalaya
between 2011 – 2013 by an international team of polar adventurers under the
umbrella of Adventurers and Scientists for Conservation (ASC). A subset of rock
samples (in triplicate) collected in the upper middle and lower levels of the alpine
biome of Pamir Mt. and the two polar sites were sampled for surface and subsurface layers under a sterile hood and examined for chemical, mineralogical and
biota by handhold X-ray fluorescence, synchrotron transmission X-ray diffraction
and stereomicroscopy.
Preliminary analysis of the data identified similarities in relative loss/retention of
major elements between polar and mountain top surfaces, process which is
different at lower altitudes. Likewise, high microbe survival rates were observed
when samples were subjected to extreme desiccations and cold conditions.
These weathering similarities of polar-like environments regardless substrate
geology together with an unexpected high microbial activity after severe lab
desiccation/temperature are promising results that entitles further analysis on the
interlink microbes-rock weathering during soil genesis at these extreme places
and how this readjusts to ongoing environmental/climate changes. Likewise the
results open up to further interesting questions such as whether these
microorganisms could can also survive long-term space conditions, which is at
the basis of one of the major hypothesis on the origins of life itself.
65

GEODAZE 2015 ABSTRACTS - University of Arizona

Transcription

Similar documents

Geology and petrology of the Catface porphyry Cu

Metamorfismo Varisco em rochas ígneas do Câmbrico Inferior

- CARBO Ceramics Inc.

CL as a versatile tool with the CamScan SEM

Vinata - Savant Explorations Ltd.

Guyana: the Lost Hadean crust of South America?

Poems - Seething and Mundham Primary School

Letter from William G. Anderson

Swallow Rocks to Big Mountain

sinifaná metasedimentites and relations with cajamarca