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Paleoproterozoic Mojave province in northwestern Mexico? Isotopic and U-Pb zircon geochronologic studies of Precambrian and Cambrian crystalline and sedimentary rocks, Caborca, Sonora

By
G. Lang Farmer
G. Lang Farmer
CIRES and Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, USAfarmer@cires.colorado.edu.
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Samuel A. Bowring
Samuel A. Bowring
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 03319, USA
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Jennifer Matzel
Jennifer Matzel
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 03319, USA
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Guadalupe Espinosa Maldonado
Guadalupe Espinosa Maldonado
Departamento de Geología, Universidad de Sonora, Hermosillo, Sonora, México
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Christopher Fedo
Christopher Fedo
Department of Geology, George Washington University, Washington, D.C. 20052, USA
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Joe Wooden
Joe Wooden
U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 90425, USA
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Published:
January 01, 2005

Whole-rock Nd isotopic data and U-Pb zircon geochronology from Precambrian crystalline rocks in the Caborca area, northern Sonora, reveal that these rocks are most likely a segment of the Paleoproterozoic Mojave province. Supporting this conclusion are the observations that paragneiss from the ≥1.75 Ga Bamori Complex has a 2.4 Ga Nd model age and contains detrital zircons ranging in age from Paleoproterozoic (1.75 Ga) to Archean (3.2 Ga). Paragneisses with similar age and isotopic characteristics occur in the Mojave province in southern California. In addition, “A-type” granite exposed at the southern end of Cerro Rajon has ca 2.0 Ga Nd model age and a U-Pb zircon age of 1.71 Ga, which are similar to those of Paleoproterozoic granites in the Mojave province. Unlike the U.S. Mojave province, the Caborcan crust contains ca. 1.1 Ga granite (Aibo Granite), which our new Nd isotopic data suggest is largely the product of anatexis of the local Precambrian basement. Detrital zircons from Neoproterozoic to early Cambrian miogeoclinal arenites at Caborca show dominant populations ca. 1.7 Ga, ca. 1.4 Ga, and ca. 1.1 Ga, with subordinate Early Cambrian and Archean zircons. These zircons were likely derived predominately from North American crust to the east and northeast, and not from the underlying Caborcan basement. The general age and isotopic similarities between Mojave province basement and overlying miogeoclinal sedimentary rocks in Sonora and southern California is necessary, but not sufficient, proof of the hypothesis that Sonoran crust is allochthonous and was transported to its current position during the Mesozoic along the proposed Mojave-Sonora megashear. One viable alternative model is that the Caborcan Precambrian crust is an isolated, autochthonous segment of Mojave province crust that shares a similar, but not identical, Proterozoic geological history with Mojave province crust found in the southwest United States

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GSA Special Papers

The Mojave-Sonora Megashear Hypothesis: Development, Assessment, and Alternatives

Thomas H. Anderson
Thomas H. Anderson
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Jonathan A. Nourse
Jonathan A. Nourse
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James W. McKee
James W. McKee
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Maureen B. Steiner
Maureen B. Steiner
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Geological Society of America
Volume
393
ISBN print:
9780813723938
Publication date:
January 01, 2005

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