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Early arc development recorded in Permian-Triassic plutons of the northern Mojave Desert region, California, USA

M. Robinson Cecil, Mary Ann Ferrer, Nancy R. Riggs, Kathleen Marsaglia, Andrew Kylander-Clark, Mihai N. Ducea and Paul Stone
Early arc development recorded in Permian-Triassic plutons of the northern Mojave Desert region, California, USA
Geological Society of America Bulletin (November 2018) 131 (5-6): 749-765


Permian-Middle Triassic plutons in the northern Mojave Desert, USA, are emplaced into the cryptic El Paso terrane, which is characterized by a northwest-striking belt of deep marine eugeoclinal strata juxtaposed against Proterozoic basement and its miogeoclinal cover. Fourteen new zircon U-Pb ages from the El Paso Mountains and Lane Mountain region of the Mojave Desert record nearly continuous magmatism occurring between ca. 275 and 240 Ma. These ages, which are taken to record the onset of subduction-related magmatism along the southwestern Laurentian margin, are older than the earliest arc plutons documented in the southern Sierra Nevada region to the north and in the Transverse Ranges to the south. They overlap, however, with Permian arc plutons documented in Sonora, Mexico. Dated plutons are compositionally variable, but can be characterized as intermediate to felsic, calcic to calc-alkalic, and having chemistries consistent with generation in an arc setting. Whole rock Sr-Nd isotopic compositions vary widely from relatively primitive (Sr (sub i) = 0.7035, initial epsilon Nd = +3, initial epsilon Hf in zircon = +13) to moderately evolved (Sr (sub i) = 0.708, initial epsilon Nd = -5, initial epsilon Hf in zircon = -3). Isotopic signatures differ considerably from partially coeval Triassic suites of the Transverse Ranges and central Mojave, which are more evolved and consistent with emplacement in Proterozoic continental crust of the Mojave province. They also differ considerably from those typical of intermediate plutons generated in intra-oceanic arcs, which are overall much more mantle-like. This suggests that the underpinnings of the El Paso terrane may be at least partly composed of continental crust and that magmas emplaced into the terrane may have been variably contaminated by crustal components. This is supported by the presence of Precambrian and early Paleozoic zircon inheritance recorded in some plutons. In all isotopic systems, values are the most evolved in the oldest plutons (ca. 275-270 Ma), becoming more juvenile in the Middle Triassic. These temporal trends, together with pluton fabrics and new estimates of Permian plate vectors, are interpreted to reflect generation of the earliest arc in a contractional setting that may have driven crustal thickening and a greater involvement of crustal materials in Permian magmas. This result supports a model of forced subduction initiation, which is favored by a change in plate motions along a previously weak margin, and predicts an initial compressive state in the upper plate. The uniformly primitive signatures of Triassic melts are taken to indicate a change to a transtensional upper-plate stress regime that promoted the development of more voluminous, primarily mantle-derived melts. Regional pluton age patterns suggest that arc magmatism initiated in restricted areas of the southwestern Laurentian margin (northern Mojave, Sonora) and then migrated north and south ultimately becoming a continuous arc by Jurassic time.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 131
Serial Issue: 5-6
Title: Early arc development recorded in Permian-Triassic plutons of the northern Mojave Desert region, California, USA
Affiliation: California State University-Northridge, Department of Geological Sciences, Northridge, CA, United States
Pages: 749-765
Published: 20181127
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 97
Accession Number: 2019-007056
Categories: Igneous and metamorphic petrologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: GSA Data Repository item 2018338; includes appendices
Illustration Description: illus. incl. 3 tables, geol. sketch maps
N35°19'60" - N35°30'00", W118°00'00" - W117°40'00"
Secondary Affiliation: Northern Arizona University, USA, United StatesUniversity of California-Santa Barbara, USA, United StatesUniversity of Arizona, USA, United StatesU. S. Geological Survey, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201906
Program Name: USGSOPNon-USGS publications with USGS authors
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