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

摘要：从内华达的南北分界线到现今的海岸，北美西部大陆地壳是由构造地形的反复增生构造而成的。其中一个事件是Golconda Allochthon （GA）的侵位，它被广泛认为是晚二叠世至早三叠纪（大约在2000年）的主要构造表现。2.4亿年前)索诺玛造山运动。然而，对现有时间限制的关键评估表明，GA向东侵位可能发生在中侏罗世——可能在索诺玛事件后75万年。对GA在北美西部晚古生代至中生代历史中的作用的可靠解释，有待于对关键领域关系的澄清，以及对约束戈尔康达逆冲构造年龄的火成岩和火山沉积岩的更精确的年龄控制。拟议的研究将通过以下组合来评估这一假设：1)有针对性的领域映射，以澄清关键领域的关系；2)构造/运动学分析，确定戈尔康达逆冲构造的搬运方向；3)利用U-Pb年代学对切割或被切割的中生代岩体进行精确测年；4)全岩同位素地球化学，比较GA内中生代岩体与邻近构造基底岩体的初始同位素比值。如果正确的话，侏罗纪时代的Golconda逆冲作用将显著影响目前对北美西部晚古生代和中生代构造演化的解释。

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.