Jurassic(?) Emplacement of the Golconda Allochthon, West-Central Nevada: Implications for the Late Paleozoic - Mesozoic Tectonic Development of Western North America

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Jurassic(?) emplacement of the Golconda Allochthon, west-central Nevada: Implications for the Late Paleozoic - Mesozoic tectonic development of western North AmericaWalter S. SnyderClyde J. NorthrupEAR-0074117ABSTRACT:From a north-south line that bifrucates Nevada to the present-day coast, the continental crust of western North America has been constructed by the repeated accretion of tectonic terrains. One of those events was the emplacement of the Golconda Allochthon (GA) which is widely regarded as the principal structural expression of the Late Permian to earliest Triassic (approx. 240 million years ago) Sonoma Orogeny. A critical evaluation of available timing constraints, however, indicates that east-directed emplacement of the GA may have occurred as late as the Middle Jurassic - perhaps 75 My after the Sonoma event. Confident interpretation of the role of the GA in the late Paleozoic to Mesozoic history of western North America awaits clarification of key field relationships and more precise age control of igneous plutons and volcano-sedimentary rocks that constrain the age of the Golconda Thrust. Proposed research will evaluate this hypothesis through a combination of: 1) targeted field mapping to clarify critical field relations; 2) structural/kinematic analysis to establish the transport direction of the Golconda Thrust; 3) U-Pb geochronology to precisely date Mesozoic plutons that either cut, or are cut by the Golconda Thrust; and 4) whole-rock isotope geochemistry to compare initial isotopic ratios of Mesozoic plutons within the GA to those of plutons in the adjacent structural basement. If valid, a Jurassic age of Golconda thrusting would significantly impact current interpretations of the late Paleozoic and Mesozoic tectonic evolution of western North America.