a volcanic eruption in the salton trough

Transcription

Geology
A VOLCANIC ERUPTION IN THE SALTON TROUGH (SOUTHERN CALIFORNIA)
DURING HUMAN PRESENCE
--Manuscript Draft-Manuscript Number:
Full Title:
A VOLCANIC ERUPTION IN THE SALTON TROUGH (SOUTHERN CALIFORNIA)
DURING HUMAN PRESENCE
Short Title:
Salton Trough eruption
Article Type:
Article
Keywords:
zircon; geochronology; obsidian; archaeometry; Lake Cahuilla
Corresponding Author:
Axel K Schmitt, Dr
University of California, Los Angeles
Los Angeles, CA UNITED STATES
Corresponding Author Secondary
Information:
Corresponding Author's Institution:
University of California, Los Angeles
Corresponding Author's Secondary
Institution:
First Author:
Axel K Schmitt, Dr
First Author Secondary Information:
Order of Authors:
Axel K Schmitt, Dr
Arturo Martin, PhD
Daniel F Stockli, PhD
Kenneth A Farley, PhD
Oscar M Lovera, PhD
Order of Authors Secondary Information:
Manuscript Region of Origin:
UNITED STATES
Abstract:
U-Th and (U-Th)/He zircon geochronology redefines the timing of volcanic activity in
the Salton Trough (southern California), the subaerial extension of the incipiently
oceanic Gulf of California. U-series disequilibrium corrected (U-Th)/He zircon analyses
for a granophyre ejecta clast from Red Island indicate an eruption age of 2,480±470 a
(between 0 and 940 BCE; error at 95% confidence). This eruption age is supported by
U-Th zircon crystallization ages for two rhyolite domes: Red Island (the host for the
granophyre) and Obsidian Butte, a prehistoric quarry for obsidian which is widely
distributed in southern California and northern Mexico archaeological sites. Lavas and
granophyre display overlapping zircon crystallization age distributions, supporting field
and compositional evidence that they are cogenetic and contemporaneous. The (UTh)/He eruption age is younger and significantly more precise than previous ages for
these volcanoes. These results are the first evidence for an eruption during human
presence in the region. They also provide an alternative explanation for the absence of
the Obsidian Butte lithic source among early prehistoric cultural artifacts which
previously been has been attributed to submergence of the quarry location during
hypothesized persistent flooding by ancient Lake Cahuilla.
Suggested Reviewers:
Kathleen Nicoll
University of Utah
[email protected]
expert on geoarchaeology
Peter Reiners
University of Arizona
Powered by Editorial Manager® and Preprint Manager® from Aries Systems Corporation
[email protected]
U-Th/He geochronology pioneer, especially for xenolith dating young volcanic samples.
Joann Stock
Caltech
[email protected]
Strong background in volcano-tectonic processes during rifting, PI for Salton Sea
Seismic Imaging project
Opposed Reviewers:
Powered by Editorial Manager® and Preprint Manager® from Aries Systems Corporation
Cover letter
Click here to download Cover letter: Letter Wyld revision v2.doc
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A VOLCANIC ERUPTION IN THE SALTON TROUGH (SOUTHERN
CALIFORNIA) DURING HUMAN PRESENCE
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Axel K. Schmitt
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Department of Earth and Space Sciences, UCLA
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Los Angeles CA 90095-1567, USA
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Phone: +310-206-5760; Email: [email protected]
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Arturo Martín
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Departamento de Geología, CICESE
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Km 107 Carr. Tijuana - Ensenada., Ensenada, B.C., México, C.P. 22800
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Daniel F. Stockli
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Department of Geological Sciences, University of Texas
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Austin, TX 78712
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Kenneth A. Farley
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Division of Geological and Planetary Sciences, California Institute of Technology
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Pasadena, CA 91125
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Oscar M. Lovera
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Department of Earth and Space Sciences, UCLA
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Los Angeles CA 90095-1567, USA
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Abstract
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U-Th and (U-Th)/He zircon geochronology redefines the timing of volcanic activity in
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the Salton Trough (southern California), the subaerial extension of the incipiently oceanic
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Gulf of California. U-series disequilibrium corrected (U-Th)/He zircon analyses for a
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granophyre ejecta clast from Red Island indicate an eruption age of 2,480±470 a
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(between 0 and 940 BCE; error at 95% confidence). This eruption age is supported by U-
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Th zircon crystallization ages for two rhyolite domes: Red Island (the host for the
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granophyre) and Obsidian Butte, a prehistoric quarry for obsidian which is widely
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distributed in southern California and northern Mexico archaeological sites. Lavas and
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granophyre display overlapping zircon crystallization age distributions, supporting field
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and compositional evidence that they are cogenetic and contemporaneous. The (U-
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Th)/He eruption age is younger and significantly more precise than previous ages for
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these volcanoes. These results are the first evidence for an eruption during human
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presence in the region. They also provide an alternative explanation for the absence of the
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Obsidian Butte lithic source among early prehistoric cultural artifacts which previously
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been has been attributed to submergence of the quarry location during hypothesized
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persistent flooding by ancient Lake Cahuilla.
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Keywords: zircon; geochronology; obsidian; archaeometry; Lake Cahuilla
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INTRODUCTION
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Volcanic chronostratigraphy is essential in understanding the timing of human origins,
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migration, and exchange. Radiometric dating of volcanic rocks down to the historical
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realm is possible in favorable cases by K-Ar (40Ar/39Ar) geochronology (e.g., the 79 CE
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eruption of Vesuvius; Renne et al., 1997; Lanphere et al., 2007), but often accuracy is
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compromised by excess 40Ar, parent-daughter mobility, or diffusive fractionation of
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Morgan et al., 2009; Flude et al., 2010).
Ar/36Ar (e.g., Cerling et al., 1985; Esser et al., 1997; McDougall and Harrison, 1999;
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(U-Th)/He geochronology of zircon as one of the first radiometric dating
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techniques (Strutt, 1908) has experienced a revival as a thermochronometer, but it is
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equally suitable for rapidly cooled volcanic rocks without subsequent thermal disturbance
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(e.g., Tagami et al., 2003; Davidson et al., 2004; Schmitt et al., 2006; Blondes et al.,
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2007). Compared to K-Ar (40Ar/39Ar) geochronology, it offers the advantages of reduced
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excess 4He due to rapid diffusion (Reiners, 2004), high daughter isotope production rates
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(4He/40Ar >20 per parent nucleus), and negligible atmospheric contamination (air Ar/He
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~2000). Its application, however, has been limited by U-series disequilibrium effects,
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which, in the case of zircon, typically cause severe age underestimation (Farley et al.,
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2002). To overcome this limitation, a novel combined U-Th ion microprobe crystal rim
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analysis and (U-Th)/He bulk crystal degassing analysis technique has been developed1.
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Here, we apply this technique to document an eruption in the Salton Trough (southern
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California) as recently as 0 - 940 BCE, and age which overlaps with human occupation of
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to equal extent at UCLA by AKS and OML, and University of Kansas by DFS
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southern California and northern Baja California, and agrees with the onset of obsidian
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use in these locations (e.g., Schaefer and Laylander, 2007).
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VOLCANISM IN THE SALTON TROUGH
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The Salton Buttes together with Cerro Prieto and Roca Consag are the
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morphologically most pristine volcanoes in the northern Gulf of California and Salton
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Trough rift zone (Fig. 1). They form an ~7 km long, NE-SW trending lineament of five
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rhyolite domes (<1 km in diameter) along the dilatational San Andreas - Imperial fault
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step-over, immediately north of the active Brawley Seismic Zone (Fig. 1). The two
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largest domes are Red Island and Obsidian Butte which consist of aphyric, glassy to
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devitrified rhyolite lava with rare oligoclase-anorthoclase phenocrysts surrounded by
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remnants of pyroclastic deposits. Where lavas developed obsidian textures, they have
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been extensively quarried for production of lithic tools during prehistoric and early post-
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Columbian times (Treganza, 1942). They also contain diverse xenoliths comprising
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unconsolidated sediment, metasediment, basalt, and granophyre (Robinson et al., 1976;
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Schmitt and Vazquez, 2006). Granophyre xenoliths are leucocratic and phaneritic with
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interstitial glass. Their radiogenic and oxygen isotopic compositions demonstrate that
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they are cogenetic with the rhyolite host, and derived from re-melting of juvenile mafic
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crust in an incipient oceanic spreading center (Schmitt and Vazquez, 2006), analogous to
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other transform fault-bounded rift segments within the Gulf of California (e.g., Lizarralde
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et al., 2007).
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PREVIOUS ERUPTION AGE CONSTRAINTS
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Geological ages
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The most commonly cited age for Salton Buttes is 33,000±35,000 a (Friedman and
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Obradovich, 1981), which supersedes an earlier K-Ar age of ~16,000 a reported in
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Muffler and White (1969). Obsidian hydration dating, now discredited (e.g., Anovitz et
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al., 1999), yielded surface exposure age estimates of 8,400 and 6,700 a for Obsidian
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Butte and 2,500 a for Red Island (Friedman and Obradovich, 1981). The emplacement of
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the Salton Buttes also closely relates to the chronology of cyclic flooding and desiccation
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of the Salton Trough. Flooding resulted from episodic northward diversion of the
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Colorado River, creating ephemeral lakes (“Lake Cahuilla”) as natural precursors to the
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modern Salton Sea. Seismically detected sequences of coarse-grained deltaic sediment
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intercalated with lake deposits imply that at least in some instances the basin entirely
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desiccated prior to inundation (Brothers et al., 2011). Subaqueous pumice deposits, wave-
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cut benches, and raft zones of reworked pumice (Kelley and Soske, 1936; Robinson et al.,
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1976) indicate emplacement prior to the ~1650 CE desiccation of Lake Cahuilla
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(Philibosian et al., 2011; cf. Waters, 1983).
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Archaeological ages
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Obsidian sourced from Obsidian Butte is distributed in the southwestern USA and
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northern Mexico, and in some cases has been documented at distances of 400-500 km
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from its source (e.g., California Channel Islands; Rick et al., 2002). Because the earliest
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use of this obsidian constrains a minimum age for Obsidian Butte, we have compiled 14C
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ages concentrating on sites that preserve a protracted record of human presence. This
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includes proximal locations in the Peninsular Ranges of southern California and northern
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Baja, and the Colorado Desert, as well as distal sites in Coastal California (Fig. 2). The
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earliest reliable artifact sourced at Obsidian Butte (Fig. 2) dates between ~640 CE and
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510 BCE (Kyle, 1996). This excludes one putative Obsidian Butte artifact (Elko Eared
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dart point C9-309; re-calibrated 14C age 1700 - 2350 BCE; McDonald, 1992), which we
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reassigned to an unknown source because its Sr abundance falls well below the 2σ limit
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for Obsidian Butte glass (Hughes, 1986). A conspicuously late onset of Obsidian Butte
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material preserved the prehistoric record (Fig. 2) is in accordance with slightly younger
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ages previously suggested (~940 CE to ~1600 CE; Hughes and True, 1985; Koerper et
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al., 1986). Older deposits in the region contain abundant obsidian artifacts procured
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dominantly from the Coso location (Fig. 1). The apparent temporal dichotomy for
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obsidian provenance from Coso vs. Obsidian Butte has previously been explained by
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inundation of Obsidian Butte with ancient Lake Cahuilla prior to the Late Prehistoric
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period (e.g., Hughes and True, 1985; Koerper et al., 1986).
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METHODS
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Sampling
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Several kg of lava were collected from outcrops at Red Island and Obsidian Butte (SB-
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04-01 and SB-04-02; Table 1). Granophyre I70-24 is a 1.5 m diameter rounded ejecta
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clast from the southern Red Island dome (Table 1; see Fig. 5 in Robinson et al., 1976).
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All sampling locations were disturbed by 20th century quarrying, and lack evidence for a
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prehistoric industry in the immediate vicinity. Abundant obsidian artifacts, however,
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occur as scattered surficial deposits in less disturbed areas of Obsidian Butte.
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Analytical procedures
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For (U-Th)/He dating, granophyre zircons were targeted because they are more abundant
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and larger than those in co-erupted lavas. Moreover, their (mostly) late Pleistocene
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crystallization ages obviate the need for 226Ra disequilibrium corrections (Farley et al.,
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2002). Zircon was separated from ~150 g rock powder (<250 µm) using heavy liquids
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and handpicked to select largely inclusion-free and intact euhedral crystals which were
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pressed into indium metal flush with the mount surface for multi-collection U-Th analysis
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using the CAMECA ims 1270 ion microprobe at UCLA. After ~5 m deep ion sputtering
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of the crystal rims, grains were extracted from their mount, photographed, and wrapped
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in platinum foil for (U-Th)/He analysis. Separate aliquots were analyzed by isotope
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dilution with a quadrupole mass spectrometer at the University of Kansas, and by peak
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height comparison with a pulse counting sector mass spectrometer at Caltech. U-series
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disequilibrium corrections for (U-Th)/He include pre-eruptive magmatic residence (from
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U-Th zircon rim crystallization ages), and zircon-melt partitioning for Pa and U (DPa/DU
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= 3; Schmitt, 2007). For comparison with 14C chronology, absolute (U-Th)/He ages were
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subtracted from the 2010 analysis date to yield calendric years (Fig. 2).
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DATING RESULTS
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Uncorrected for U-series disequilibrium, the average (U-Th)/He zircon age for
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Red Island granophyre I70-24 is ~1,600 a (Table 1). U-series disequilibrium corrections
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(Farley et al., 2002) increase this age to 2,480±470 a (mean square of weighted deviates
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MSWD = 2.6; n = 27; Table 1), or between 0 and 940 BCE in calendric years (at 95%
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confidence; Fig. 2). Error propagation includes uncertainties from 4He, Th, and U isotope
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dilution analysis, morphometric measurements required for the α-ejection correction, and
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rim crystallization ages. The slightly elevated MSWD for the population, however,
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suggests a remainder of unaccounted error. We attribute this to internal zonation of the
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crystals, both with regard to age and U and Th abundance, which would impact
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disequilibrium and α-ejection corrections, respectively. Although it is conceivable to
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better constrain internal zonation through ion microprobe depth profiling, the lengthy
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analysis would make this impractical for a large number of crystals. We instead analyzed
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multiple crystals rationalizing that this will empirically account for variations in
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crystallization ages and U and Th abundance. Excess scatter resulting from unaccounted
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analytical error is propagated by multiplying the weighted average age uncertainty with
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the square root of the MSWD (Table 1).
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U-Th zircon rim crystallization ages for granophyre I70-24 (Fig. 3;
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Supplementary Table 1) display significant variations ranging from near eruption to
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~30,000 a (MSWD = 25). The average rim crystallization age is 26,200±1,000 a (MSWD
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= 2.4; n = 35), with the exception of two younger rims, one of which overlaps with the
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(U-Th)/He eruption age (Fig. 3). The U-Th zircon crystallization ages in both lavas are
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statistically indistinguishable (Kolmogorov-Smirnov probability of equivalence = 0.55),
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but their overall age range exceeds analytical uncertainties as indicated by the elevated
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MSWD for the population (MSWD = 3.2; n = 51). Unmixing models (Sambridge and
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Compston, 1994) deconvolve the U-Th crystallization age spectrum into two age peaks at
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5,500±1,200 and 12,100±1,800 a at sub-equal abundance (Fig. 3). The precision of
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individual crystal ages, however, is insufficient to distinguish discrete crystallization
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pulses vs. continuous crystallization over this time interval. Regardless, the results from
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the unmixing model imply that a significant zircon population in both lavas continued to
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crystallize in the magma until immediately before the eruption.
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DISCUSSION
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Eruptive and intrusive activity in the Salton Trough
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Because rapid cooling is expected after surficial emplacement of the granophyre xenolith
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in its host lava, the (U-Th)/He zircon age is reasonably interpreted to date the eruption of
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Red Island dome. The (U-Th)/He zircon eruption age is fully consistent with the U-Th
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crystallization ages, which lends independent support to its accuracy. Both are
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significantly younger than the commonly accepted K-Ar age. Possibly, this is due to
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excess 40Ar in volcanic glass, whereas we do not expect excess 4He in zircon due to rapid
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Coincidentally, Red Island obsidian hydration ages agree with the (U-Th)/He age, but we
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refer to Anovitz et al. (1999) for a discussion of fundamental problems inherent to this
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method.
He diffusion at magmatic temperatures experienced by the granophyre prior to eruption.
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The similarity in U-Th crystallization ages for volcanic and plutonic samples
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implies that they collectively represent protracted zircon crystallization in a long-lived
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(relative to the time since the eruption) and hence potentially active magma reservoir.
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This commonality is underscored by zircon oxygen isotopic and trace element affinities
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between lavas and granophyres (Schmitt and Vazquez, 2006). Although the (U-Th)/He
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eruption age is strictly for Red Island, the similarity in composition and U-Th
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crystallization ages for Red Island and Obsidian Butte is permissive for both being
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coevally emplaced, in accordance with the notion that the Salton Buttes share a fault-
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controlled feeder dike at depth (Robinson et al., 1976).
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Obsidian cultural availability and Holocene Lake Cahuilla
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(U-Th)/He zircon geochronology is a novel Quaternary dating tool, and although
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its application to archaeological samples is restricted by the destructive nature of crystal
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extraction from comparatively large samples (in particular for obsidian), it has potential
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for volcanic chronostratigraphy in an archaeological context. The young eruption age for
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Red Island is concordant with archaeological evidence for an exclusively late prehistoric
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(sensu lato) use of the Obsidian Butte lithic resource (Fig. 2). Under the assumption that
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“Obsidian Butte glass has been around for a long time” (Hughes and True, 1985), the
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absence of Obsidian Butte artifacts in older deposits has been previously attributed to the
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persistent presence of ancient Lake Cahuilla, which would have submerged the lavas
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below nearly 80 m of water during its high-stands (e.g., Hughes and True, 1985). A much
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more recent eruption age for Obsidian Butte, as proposed here, can explain this absence
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and obviate the need to postulate continuous inundation, a hydrologic pattern which
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would depart from frequent lake desiccation and filling cycles that have been documented
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for the past ~2,000 years (Waters, 1983; Philibosian et al., 2011; Brothers et al., 2011).
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CONCLUSIONS
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By combining (U-Th)/He and U-Th zircon geochronology, we have dated quasi-
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continuous late Pleistocene to Holocene intrusive activity in the Salton Trough that
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culminated in explosive and effusive eruption of rhyolite at 2,480±470 a (between 0 and
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940 BCE). The (U-Th)/He zircon eruption age for Red Island is one of the youngest in
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southern California, overlapping within uncertainty with the phreatomagmatic eruption of
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Ubehebe Crater in Death Valley (Sasnett et al., 2012). It is the first reliable evidence that
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the Salton Trough has been volcanically active during human presence. Protracted zircon
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crystallization ages indicate magmatic longevity and imply potential for future activity.
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The consistency of combined U-Th and (U-Th)/He zircon chronology with archeological
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ages for obsidian use underscores that this method has strong potential for Quaternary
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volcanic chronostratigraphy and archaeometry.
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ACKNOWLEDGEMENTS
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Wilfred Elders is thanked for providing sample I70-24. We thank Lindsey Hedges and
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Roman Kislitsyn for (U-Th)/He analytical assistance, and Haibo Zou and Chuan-Chou
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Shen for whole-rock U-Th isotope data. This work was supported by grants through UC-
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MEXUS CN 07-60 and NSF MARGINS EAR-0948162. The ion microprobe facility at
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UCLA is partly supported by a grant from the Instrumentation and Facilities Program,
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Division of Earth Sciences, National Science Foundation.
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Dating into the historical realm: calibration against Pliny the Younger: Science, v.
319
277, p. 1297-1280.
320
Rick, T.C., Skinner, C.E., Erlandson, J.M., and Vellanoweth, R.L., 2002, Obsidian
321
Source Characterization and Human Exchange Systems on California’s Channel
322
Islands: Pacific Coast Archaeological Society Quarterly, v. 37(3), p. 28-44.
323
Robinson, P.T., Elders, W.A., and Muffler, L.J.P., 1976, Quaternary Volcanism in Salton
324
Sea Geothermal Field, Imperial-Valley, California: Geological Society of
325
America Bulletin, v. 87, p. 347-360.
326
Sambridge, M.S., Compston, W., 1994, Mixture modeling of multi-component data sets
327
with application to ion-probe zircon ages: Earth and Planetary Science Letters, v.
328
128, p. 373–390.
329
Sasnett, P., Goehring, B.M., Christie-Blick, N., and Schaefer, J.M., 2012, Do
330
phreatomagmatic eruptions at Ubehebe Crater (Death Valley, California) relate to
331
a wetter than present hydro-climate?: Geophysical Research Letters, v. 39,
332
L02401, doi:10.1029/2011GL050130.
333
Schaefer, J., Laylander, D., 2007, The Colorado Desert: Ancient adaptations to wetlands
334
and wastelands, in Jones, T.J., Klar, K.A., California Prehistory: Colonization,
335
Culture, and Complexity: Rowman, Altamira, p. 247-257.
15
336
Schmitt, A.K., 2007, Ion microprobe analysis of 231Pa/235U and an appraisal of
337
protactinium partitioning in igneous zircon: American Mineralogist, v. 92, p 691-
338
694.
339
Schmitt, A.K., and Vazquez, J.A., 2006, Alteration and remelting of nascent oceanic
340
crust during continental rupture: Evidence from zircon geochemistry of rhyolites
341
and xenoliths from the Salton Trough, California: Earth and Planetary Science
342
Letters, v. 252, p. 260-274.
343
Schmitt, A.K., Stockli, D.F., and Hausback, B.P., 2006, Eruption and magma
344
crystallization ages of Las Tres Virgenes (Baja California) constrained by
345
combined 230Th/238U and (U-Th)/He dating of zircon: Journal of Volcanology and
346
Geothermal Research, v. 158, p. 281-295.
347
348
349
Strutt, R.J., 1908, Helium and radio-activity in rare and common minerals: Proceedings
of the Royal Society London A., v. 80, p. 572-594.
Tagami, T., Farley, K.A., and Stockli, D.F., 2003, (U-Th)/He geochronology of single
350
zircon grains of known Tertiary eruption age: Earth and Planetary Science Letters
351
v. 207, p. 57-67.
352
353
354
355
Treganza, A.E., 1942, An Archaeological Reconnaissance of Northeastern Baja
California and Southeastern California, American Antiquity, v. 8(2), p. 152-163.
Waters, M.R., 1983, Late Holocene lacustrine chronology and archaeology of ancient
Lake Cahuilla, California: Quaternary Research, v. 19, p. 373-387.
356
357
FIGURE CAPTIONS
16
358
Fig. 1: Northern Gulf of California and Salton Trough map showing Quaternary
359
volcanoes (red triangles) and major faults (solid black lines; SAF = San Andreas; IF =
360
Imperial; CPF = Cerro Prieto). Maximum extent of Pleistocene – Holocene Lake Cahuilla
361
(i.e., the fill line at +12 m above sea-level) is indicated (after Brothers et al., 2011). BSZ
362
= Brawley Seismic Zone; WB = Wagner basin. Inset A shows study region with
363
archaeological locations (1 San Diego; 2 Anza-Borrego; 3 Coachella Valley; 4 Zaragoza,
364
5 Channel Islands; 6 Coso). Inset B details locations for the Salton Buttes domes (red).
365
366
Fig. 2: (A) Lake Cahuilla high-stand chronology (blue boxes; Philibosian et al., 2011)
367
and obsidian artifact ages from Channel Island (B), Peninsular Ranges and Colorado
368
Desert sites (C) in comparison with Red Island (U-Th)/He eruption age (red bar). Artifact
369
ages are calibrated 14C calendar ages (2σ) from the same stratum or section shown as
370
exact or bracketing (bars), maximum (left arrows), or minimum (right arrows) ages. Solid
371
bars: Obsidian Butte; open bars: undifferentiated sources (supplementary table 3).
372
Numbers indicate references for archaeological data (locations in Fig. 1): 1 = Kyle
373
(1996); 2 = McDonald (1992); 3 = Love and Dahdul (2002); 4 = Porcayo-Michelini,
374
2006; 5 = Rick et al. (2002); Erlandson et al. (2011).
375
376
Fig. 3: (A) Rank-order and relative probability plots for (U-Th)/He zircon ages from Red
377
Island granophyre I70-24. U-Th crystallization ages from two-point zircon – whole-rock
378
isochrons for (B) granophyres and (C) lava samples, respectively. Gaussian curves in C
379
indicate subpopulations from unmixing models.
380
17
381
TABLES
382
Table 1: (U-Th)/He zircon age summary for Red Island granophyre ejecta clast I70-24
383
384
SUPPLEMENTARY DATA
385
Electronic Appendix 1: Sampling and zircon methodology
386
Supplementary Table 1: 230Th-238U results for Salton Buttes zircons and whole-rocks
387
Supplementary Table 2: (U-Th)/He results for Salton Buttes zircons
388
Supplementary Table 3: 14C ages for XRF-sourced obsidian
389
390
Manuscript for submission to: GEOLOGY
391
Word/character count:
392
Text: 15657 characters (incl. spaces) = 2.2 pages
393
Acknowledgements, References Cited, and figure captions: 9830 characters (incl. spaces) = 1.1 pages
394
3 Figures, 1 Table = 0.7 pages
395
Total = 4 pages
396
18
A
115°
lto
Salton
Buttes
Red
Island
Obsidian
Butte
N
BSZ
IF
6
0 1 2 km
Lake Cahuila
shoreline Cerro Prieto
Gila Rive
5
su
lar
4
es
ng
Ra
Sonora
32°
Co
lo
Riv rado
er
nin
2
CP
F
Pe
3
r
Desert
California
Baja
Sa
Colorado
gh
1
B
n
116°
S
Sa AF
lto
nT
rou
117°
Se
a
Figure 1
Click here to download Figure: Schmitt et al Fig1 revised.pdf
116°
Fig. 1: Schmitt et al.
Roca
115° Consag
WB
114°
Figure 2
Click here to download Figure: Schmitt et al Fig2.pdf
(U-Th)/He eruption age (2σ confidence)
A Lake Cahuilla high-stands
undated
B Channel Island obsidian artifacts
C Peninsular Range and Colorado Desert obsidian artifacts
2
2
2
2
4
}
to ~12,000 BCE
5
Salton Buttes
other sources
2
3
1
2
22
2
2
CE
2
BCE
calendar years
Figure 3
Click here to download Figure: Schmitt et al Fig3.pdf
2,480±470 a (2σ; MSWD=2.6; n=27)
Lab 1
Lab 2
(U-Th)/He zircon eruption
26,200±1,000 a (2σ)
97%
U-Th zircon crystallization
granophyre (n=37)
2,990±1260 a (2σ)
3%
Red Island
Obsidian Butte
12,100±1,800 a (2σ)
51%
5,500±1,200 a (2σ)
49%
U-Th zircon crystallization
lava (n=51)
age [a]
0
10,000 20,000 30,000 40,000 50,000
Table 1
Table 1: (U-Th)/He zircon age summary for Red Island granophyre ejecta clast I70-24
1
Lab 1 (Caltech)
Lab 2 (KU)
combined
1
2
(U-Th)/He age
±
years
1440 500
1620 260
1520 260
2
(U-Th)/He age
±
years
3.2
2280 780
0.85
2650 600
1.8
2480 470
MSWD
U-decay series equilibrium
corrected for U-series disequilibrium
miniumum-maximum
4
rim ages determined at UCLA
MSWD = mean square of weighted deviates; n = number of replicate crystals
all uncertainties 2σ (analytical) multiplied with square-root of MSWD
sampling location N33°11'51.3'', W115°36'44.2'' (Robinson et al., 1976)
3
MSWD
3.2
2.2
2.6
3
U
ppm
11 205-471
16 143-1898
27 143-1898
n
Th/U
3
0.59-0.73
0.55-0.90
0.55-0.90
3
4
mass U-Th crystallization age
µg
years
6.2-37
20000-37900
7.5-31
2980-34000
6.2-37
2980-37900
Supplemental file 1
Click here to download Supplemental file: Supplementary_data_1.xlsx
Supplementary data table 1: U-Th analyses
sample/analysis
Red Island granophyre
2008_07_05July\ [email protected]
2010_08_10Aug\ [email protected]
I70-24
rhyolite lava
2005_11_29Nov\ SB0402MLT4_g2_s1.ais
2005_02_14Feb\ SB0401_g1_s1.ais
2005_02_14Feb\ SB0402_g9_s1.ais
2005_02_13Feb\ SB0402_g7_s1.ais
2005_11_29Nov\ SB0402MLT4_g6_s1.ais
2005_02_14Feb\ SB0401_g7_s1.ais
2005_02_14Feb\ SB0401_g10_s1.ais
2005_11_29Nov\ SB0402MLT4_g3_s1.ais
2005_11_29Nov\ SB0402MLT4_g5_s1.ais
2005_02_14Feb\ SB0401_g9_s1.ais
2005_02_14Feb\ SB0401_g6_s1.ais
2005_02_13Feb\ SB0402_g1_s1.ais
2005_11_29Nov\ SB0402MLT4_g1_s1.ais
2005_02_14Feb\ SB0402_g10_s1.ais
2005_02_14Feb\ SB0402_g8_s1.ais
2005_02_14Feb\ SB0401_g5_s1.ais
2005_02_13Feb\ SB0402_g2_s1.ais
2006_08_30Aug\ SB0401_Buff2_g1_s1.ais
2006_08_30Aug\ SB0401_Buff2_g2_s1.ais
2006_08_30Aug\ SB0401_Buff2_g3_s1.ais
2006_08_30Aug\ SB0402_Buff2_g1_s1.ais
2006_08_30Aug\ SB0402_Buff2_g2_s1.ais
2006_08_30Aug\ SB0402_Buff2_g3_s1.ais
2006_08_30Aug\ SB0402_Buff2_g4_s1.ais
2006_08_30Aug\ SB0401_Buff2_g4_s1.ais
2006_08_30Aug\ SB0401_Buff2_g2_s1B.ais
2008_02_01Feb\ [email protected]
material
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
whole-rock
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
analysis type
238
(
232
U)/(
Th)
±
230
(
232
Th)/(
Th)
±
age [ka]
+ [ka]
- [ka]
U [ppm]
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
-
6.04
5.80
6.82
7.14
7.97
5.65
9.48
7.40
5.48
6.21
2.82
9.36
3.14
7.35
5.55
5.16
4.90
15.05
6.01
6.30
5.02
6.97
10.09
5.25
5.70
7.26
4.88
4.81
7.21
5.13
4.59
5.23
5.10
6.50
5.87
4.32
6.17
0.696
0.03
0.11
0.07
0.18
0.16
0.02
0.84
0.15
0.03
0.03
0.03
0.33
0.04
0.19
0.07
0.06
0.05
1.49
0.11
0.07
0.06
0.11
0.17
0.08
0.09
0.47
0.06
0.06
0.15
0.10
0.06
0.06
0.07
0.17
0.09
0.05
0.17
0.002
2.18
1.78
1.87
2.59
2.80
2.19
2.53
2.45
2.16
2.27
1.42
2.61
1.45
2.23
2.19
1.98
1.78
3.69
2.06
1.13
1.96
2.65
2.00
2.14
2.25
2.15
2.15
2.07
2.46
2.07
1.88
1.83
2.26
2.00
1.84
1.84
2.14
0.974
0.29
0.18
0.20
0.16
0.15
0.16
0.22
0.15
0.16
0.16
0.04
0.16
0.05
0.10
0.09
0.09
0.06
0.47
0.09
0.03
0.08
0.16
0.10
0.09
0.14
0.10
0.10
0.09
0.13
0.13
0.09
0.07
0.12
0.08
0.10
0.07
0.05
0.004
27.8
18.6
17.3
31.5
31.6
30.7
21.3
27.2
31.1
29.3
25.8
22.9
23.8
22.8
31.7
27.8
23.3
22.9
24.9
2.98
28.3
34.0
12.7
32.4
32.1
21.6
36.1
33.8
28.3
31.1
29.0
22.7
37.9
21.3
20.0
30.0
26.1
-
8.0
4.9
4.4
4.0
3.2
4.8
4.1
3.4
4.9
4.2
2.9
2.7
3.2
2.2
3.0
3.0
2.0
5.2
2.4
0.63
2.6
3.9
1.4
2.9
4.2
2.7
3.6
3.5
2.9
4.3
3.4
2.2
4.5
1.9
2.5
2.9
1.6
-
-7.5
-4.7
-4.2
-3.8
-3.1
-4.6
-3.9
-3.3
-4.7
-4.1
-2.8
-2.6
-3.1
-2.2
-2.9
-2.9
-2.0
-5.0
-2.4
-0.63
-2.5
-3.8
-1.4
-2.9
-4.1
-2.7
-3.5
-3.4
-2.8
-4.1
-3.3
-2.2
-4.3
-1.9
-2.4
-2.8
-1.6
-
266
560
750
1386
1321
364
463
1408
483
750
341
3759
2039
2205
3383
782
864
460
793
3344
776
230
1155
484
421
1343
1316
629
887
1110
997
1006
716
1289
548
1022
1848
3.482
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
interior
rim
rim
rim
rim
rim
rim
rim
3.16
3.14
5.05
3.04
4.81
2.83
5.37
4.99
5.69
5.36
5.56
4.01
2.23
2.09
6.27
3.94
6.19
4.90
4.33
5.03
5.47
7.26
7.02
6.29
5.34
2.83
5.10
5.43
5.02
6.01
5.79
6.00
6.51
0.01
0.05
0.02
0.02
0.03
0.01
0.03
0.06
0.03
0.09
0.04
0.18
0.03
0.01
0.03
0.01
0.12
0.04
0.18
0.04
0.04
0.09
0.04
0.04
0.09
0.03
0.03
0.03
0.03
0.04
0.04
0.04
0.08
1.03
1.09
1.22
1.09
1.25
1.10
1.32
1.32
1.39
1.40
1.52
1.34
1.11
1.10
1.77
1.42
1.77
1.32
1.03
1.61
1.42
1.54
1.47
1.61
1.41
1.12
1.14
1.36
1.27
1.12
1.05
1.30
1.24
0.04
0.02
0.06
0.02
0.10
0.02
0.06
0.08
0.14
0.11
0.10
0.06
0.04
0.02
0.12
0.05
0.07
0.06
0.05
0.08
0.10
0.18
0.11
0.13
0.07
0.02
0.06
0.08
0.06
0.09
0.08
0.10
0.13
1.83
4.45
6.19
5.17
7.43
6.17
8.13
8.95
9.48
10.4
13.2
12.9
10.3
9.81
16.9
16.4
17.3
9.36
1.20
17.5
10.7
9.75
8.75
13.2
10.6
7.29
3.70
9.29
7.62
2.78
1.31
6.61
4.86
2.08
1.21
1.86
1.56
3.08
1.75
1.83
2.50
3.65
3.0
2.8
2.9
4.4
2.22
3.1
2.4
2.0
1.86
1.92
2.8
2.7
3.56
2.28
3.2
2.0
1.79
1.85
2.21
1.95
2.06
1.83
2.34
2.80
-2.04
-1.19
-1.83
-1.54
-3.00
-1.72
-1.80
-2.44
-3.53
-2.9
-2.7
-2.8
-4.2
-2.18
-3.0
-2.4
-1.9
-1.83
-1.89
-2.7
-2.6
-3.45
-2.23
-3.1
-1.9
-1.76
-1.82
-2.17
-1.91
-2.02
-1.80
-2.29
-2.73
1554
4442
790
3441
601
3551
788
448
389
522
408
771
4646
3007
493
960
817
450
307
455
233
258
219
154
2008_05_24May\ [email protected]
SB0402
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
zircon
whole-rock
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
rim
-
5.93
4.91
5.05
5.50
5.57
5.51
5.51
5.75
5.71
5.48
5.33
5.79
4.95
5.78
5.84
5.66
6.48
6.11
0.923
analytical errors 1σ
SB0401 sampled at Red Island: N 33°11’59.1’’; W 115°36’44.3’’
SB0402 sampled at Obsidian Butte: N 33°10’14.6’’; W 115°38’03.1’’
2005 data: Schmitt and Vazquez (2006); 2006 data: Schmitt (2007)
Decay constants used: λ230: 9.1577 ·10-6 a-1; λ232: 4.9475·10-11 a-1; λ238: 1.55125·10-10 a-1
0.03
0.19
0.16
0.03
0.05
0.03
0.04
0.03
0.02
0.05
0.05
0.03
0.10
0.05
0.03
0.04
0.05
0.04
0.001
1.27
1.13
1.61
1.41
1.34
1.58
1.48
1.36
1.22
1.45
1.50
1.23
1.34
1.55
1.54
1.32
1.90
1.48
0.997
0.10
0.11
0.14
0.14
0.13
0.13
0.14
0.24
0.14
0.11
0.13
0.14
0.12
0.16
0.19
0.16
0.21
0.20
0.004
6.16
3.84
17.7
10.4
8.26
14.7
12.1
8.51
5.14
11.4
13.3
5.32
9.60
13.3
12.7
7.71
19.3
10.8
-
2.48
3.21
4.7
3.8
3.48
3.7
3.9
6.07
3.39
3.1
3.7
3.50
3.67
4.1
4.8
4.24
5.1
4.9
-
-2.43
-3.12
-4.5
-3.7
-3.37
-3.6
-3.8
-5.75
-3.29
-3.0
-3.6
-3.40
-3.55
-4.0
-4.6
-4.08
-4.9
-4.7
182
339
215
542
563
516
494
457
506
641
578
415
806
509
371
490
384
293
5.987
Supplemental file 2
Supplementary data table 2: (U-Th)/He zircon analyses of Red Island granophyre
Sample
lab
zI7024-1-1
zI7024-1-2
zI7024-1-3
zI7024-1-4
zI7024-1-5
zI7024-1-6
zI7024-1-7
zI7024-1-8
zI7024-1-9
zI7024-1-10
zI7024-2-1
zI7024-2-2
zI7024-2-3
zI7024-2-4
zI7024-2-5
zI7024-2-6
zI7024-2-7
zI7024-2-9
zI7024-2-10
zI7024-2-11
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
KU
z7024-2-12
z7024-2-13
z7024-2-15
z7024-2-17
z7024-2-18
z7024-2-19
z7024-2-20
z7024-2-21
z7024-2-22
z7024-2-23
z7024X-1
z7024X-2
z7024X-3
Caltech
Caltech
Caltech
Caltech
Caltech
Caltech
Caltech
Caltech
Caltech
Caltech
Caltech
Caltech
Caltech
Age [ka]
(U-Th)/He equilibrium
1.79
2.29
2.09
1.71
40.21
1.78
1.32
1.94
1.66
1.10
19.86
3.35
7.29
38.16
1.54
18.16
4.21
2.05
1.32
6.11
-5.14
4.46
1.08
2.15
3.80
1.95
0.95
2.16
2.71
4.64
2.89
1.00
3.42
± [ka]
0.50
0.64
0.58
0.48
11.22
0.50
0.37
0.54
0.46
0.31
5.54
0.94
2.03
10.65
0.43
5.07
1.17
0.57
0.37
1.70
-1.43
1.25
0.30
0.60
1.06
0.54
0.27
0.60
0.76
1.30
0.81
0.28
0.95
Age [ka]
(U-Th)/He disequilibrium
2.82
3.94
3.70
2.64
40.21
2.73
2.07
2.88
2.52
1.71
19.86
5.18
12.09
38.16
3.18
18.16
6.90
3.36
1.98
10.28
-5.14
6.68
1.67
3.58
6.50
2.88
1.52
3.55
4.12
7.05
4.90
1.64
5.12
Decay constants used: λ230: 9.1577 ·10-6 a-1; λ232: 4.9475·10-11 a-1; λ238: 1.55125·10-10 a-1
U [ppm]
Th [ppm]
Th/U
mass [ug]
Ft
D230
7.7
4.8
4.3
3.9
3.2
4.7
4.0
3.3
4.8
4.2
3.0
2.0
5.1
2.4
0.6
2.6
3.9
2.9
4.2
2.7
316
290
475
330
50
299
439
590
383
487
310
520
328
396
1898
406
258
143
308
382
180
196
275
263
129
200
333
434
285
365
204
466
200
284
1052
270
163
90
237
228
0.57
0.68
0.58
0.80
2.57
0.67
0.76
0.73
0.74
0.75
0.66
0.90
0.61
0.72
0.55
0.66
0.63
0.63
0.77
0.60
17.0
26.0
14.1
20.9
4.9
8.0
18.9
16.9
11.2
14.8
19.5
8.4
30.5
6.0
7.5
9.4
20.3
23.2
28.6
10.1
0.83
0.85
0.82
0.85
0.76
0.79
0.83
0.83
0.81
0.82
0.84
0.80
0.86
0.77
0.74
0.79
0.81
0.85
0.85
0.80
0.181
0.215
0.185
0.254
0.820
0.214
0.242
0.234
0.237
0.239
0.210
0.286
0.194
0.229
0.177
0.212
0.201
0.201
0.246
0.191
-1.43
1.94
0.46
0.96
1.74
0.84
0.42
1.01
1.16
2.05
1.34
0.45
1.53
36.1
33.8
31.1
29.0
22.7
37.9
21.3
20.0
30.0
26.1
25.6
25.6
25.6
3.6
3.5
4.2
3.4
2.2
4.4
1.9
2.5
2.9
1.6
2.3
2.3
2.3
358
264
367
354
252
327
471
205
259
446
256
414
240
228
173
258
210
168
208
338
124
187
322
159
253
177
0.64
0.65
0.70
0.59
0.67
0.64
0.72
0.60
0.72
0.72
0.62
0.61
0.73
5.6
5.5
11.0
7.6
7.5
13.1
10.2
37.2
9.5
6.2
20.6
20.6
24.8
0.76
0.77
0.81
0.79
0.78
0.82
0.81
0.87
0.80
0.77
0.84
0.84
0.86
0.203
0.208
0.224
0.190
0.213
0.203
0.229
0.193
0.230
0.231
0.198
0.195
0.234
- [ka]
± [ka]
0.92
0.93
0.95
0.62
11.22
0.83
0.60
0.95
0.68
0.42
5.54
1.19
3.87
10.65
0.91
5.07
1.55
0.75
0.56
3.05
0.73
1.21
1.10
0.82
11.22
0.72
0.56
0.71
0.72
0.50
5.54
1.54
3.28
10.65
0.83
5.07
2.13
1.07
0.55
2.71
-1.43
2.17
0.44
0.84
1.48
0.93
0.42
1.13
1.21
2.31
1.15
0.43
1.75
-1.43
1.70
0.48
1.08
1.99
0.75
0.43
0.89
1.11
1.79
1.53
0.47
1.30
analytical errors stated at 1σ
KU = He mass spectrometry at University of Kansas, Caltech = He mass spectrometry at Californa Institute of Technology
strikethrough = excluded (see comment)
D230 = [(Th/U)zircon/(Th/U)whole-rock]×(230Th)/(238U)whole-rock
D231 = 3 (Schmitt, 2007)
± [ka]
0.82
1.07
1.02
0.72
11.22
0.78
0.58
0.83
0.70
0.46
5.54
1.37
3.58
10.65
0.87
5.07
1.84
0.91
0.55
2.88
Age [ka]
U-Th rim crystallization
27.8
18.6
17.3
31.5
31.6
30.7
21.3
27.2
31.1
29.3
27.8
23.3
22.9
24.9
3.0
28.3
34.0
32.4
32.1
21.6
+ [ka]
comment
U peak miscentering
partial crystal loss after laser heating
initial set-up
initial set-up
Supplemental file 3
Site
SRI-3
SRI-4
SRI-147
SMI-1
SMI-172
SNI-351
SMI-172
SNI-168
SNI-171
SNI-8
SCRI-240
SRI-19
SCRI-1
SRI-2
SCRI-191
SCRI-236
SCRI-474
SMI-528
SCRI-474
SRI-9
SRI-60
SNI-25
SMI-163
SCI-1487
SCI-126
SRI-512
SDi-2537
SDi-2537
SDi-2537
SDi-2537
SDi-2537
SDi-2537
SDi-2537
SDi-2537
SDi-2537
SDi-2537
SDi-10148
RIV-2936
Zaragoza
maximum
minimium
BCE 6350
BCE 5450
BCE 5450
BCE 5150
BCE 4490
BCE 3920
BCE 3490
BCE 2890
BCE 2100
BCE 1880
BCE 1260
BCE 1010
unknown
BCE 50
BCE 30
240
420
470
780
1270
1300
1350
1630
BCE 11,355
BCE 2350
BCE 2900
BCE 2900
<1450
BCE 510
BCE 180
890
BCE 410
BCE 150
BCE 3630
BCE 1300
BCE 4320
1260
BCE 3320
1640
BCE 300
BCE 1690
1450
BCE 740
BCE 610
1750
1650
1410
640
830
1010
1440
1720
1410
1680
>1500
>1500
BCE 12,010
>1500
<BCE 2350
>1160
BCE 1700
>1450
>750
1400
1400
>1400
640
645
1020
n artifacts source
reference
1
2
1
5
6
1
2
1
1
1
1
1
1
1
7
2
3
3
2
1
2
1
1
1
2
1
3
4
1
1
2
16
2
12
1
5
1
debitage
2
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Rick et al. (2001)
Erlandson et al. (2011)
McDonald (1992)
McDonald (1992)
McDonald (1992)
McDonald (1992)
McDonald (1992)
McDonald (1992)
McDonald (1992)
McDonald (1992)
McDonald (1992)
McDonald (1992)
Kyle (1996)
Love and Dahdul (2002)
Porcayo-Michelini (2006)
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Other
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Coso
Obsidian Butte
Obsidian Butte
Coso
Obsidian Butte
Obsidian Butte
Obsidian Butte
unknown
San Felipe
San Felipe
San Felipe (?)
Obsidian Butte
Obsidian Butte
Obsidian Butte
Obsidian Butte
Coso
Obsidian Butte
all sites with prefix CA except Zaragoza (Baja California, Mexico)
all ages CE (unless indicated) with minimum and maximum ages at 2σ
absolute ages reported in literature were recalcualted to calendric ages using OxCal v. 3.10
references:
Erlandson, J.M., Rick, T.C., Braje, T.J., Casperson, M., Culleton, B., Fulfrost, B., Garcia, T., Guthrie, T.A., Jew, N., Kennett, D.J., M
Kyle, C.E., 1996, A 2,000 year old milling tool kit from CA-SDI-10148, San Diego, California: Pacific Coast Archaeological Society
Love, B., and Dahdul, M., 2002, Desert chronologies and the Archaic period in the Coachella Valley. Pacific Coast Archaeologica
McDonald, A.M., 1992, Indian Hill rockshelter and aboriginal cultural adaptation in Anza-Borrego State Park, southeastern Cali
Porcayo-Michelini, A., 2006, Informe final para el consejo de arqueología de los trabajos arqueologícos realizados en el sitio Ig
Rick, T.C., Skinner, C.E., Erlandson, J.M., and Vellanoweth, R.L., 2002, Obsidian Source Characterization and Human Exchange S
T.A., Jew, N., Kennett, D.J., Moss, M.L., Reeder, L., Skinner, C., Watts, J., Willis, L., 2011, Paleoindian Seafaring, Maritime Technologies, and
Coast Archaeological Society Quarterly, v. 32(4), p. 76-87.
y. Pacific Coast Archaeological Society Quarterly, v. 38(2-3), p. 66-86.
State Park, southeastern California [Ph.D. thesis]: Riverside, University of McDonald, A.M., 1992, Indian Hill rockshelter and aboriginal cult
ogícos realizados en el sitio Ignacio Zaragoza. Archivo del Centro INAH, Baja California.
ation and Human Exchange Systems on California’s Channel Islands: Pacific Coast Archaeological Society Quarterly, v. 37(3), p. 28-44.
ritime Technologies, and Coastal Foraging on California’s Channel Islands: Science, v. 331, p. 1181-1185.
helter and aboriginal cultural adaptation in Anza-Borrego State Park, southeastern California [Ph.D. thesis]: Riverside, University of Califor
y, v. 37(3), p. 28-44.
side, University of California, 429 p.

a volcanic eruption in the salton trough

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