Evolution of Cordilleran Lithosphere: Transition From Mesozoic Shortening to Cenozoic Extension, East-Central Nevada

美国西部科迪勒兰的地质历史是复杂的，关于其深层地壳结构的问题越来越多。从中生代的板块收敛和地壳缩短到新生代的分裂和伸展，其地质构造是如何形成的，是目前争论最多的问题。在今天的盆地和山脉省，这个过渡时期的特征是浅板块俯冲和弧岩浆作用的关闭，大约70-50亿年前，随后发生了历史上最大的火山喷发事件之一，大约45-20亿年前，为中新世盆地和山脉的断裂奠定了基础。这项研究的重点是在盆地和山脉省中部（内华达州中东部和邻近的犹他州）的这个过渡时期对发生的事件进行更好的绝对年龄定位，以解决当前关于这段历史的争议，并为这段时间范围产生更全面的全地壳模型。多学科和全面的方法将相互配合：1。详细研究了岩浆岩浆岩中异晶/继承锆石种群的U-Pb辐射年龄、微量元素和同位素地球化学特征，揭示了深部地壳的温度-时间历史2。构造/微结构研究，结合岩石学、地质年代学和热年代学的关键岩石样带，将Snake Range变质核杂岩中推断的地壳深层与近表层联系起来——在这个地方，变形和冷却历史在非常厚的地壳与较薄的地壳之间的争论以及它在过渡时期地壳流动和崩塌中的作用中占据突出地位。3. 沉积盆地的时空演化，其历史为地貌演化、与火山爆发的关系以及岩心复合体深部岩石断层隆升的开始提供了一套强有力的、明确的约束条件。这种全面的方法将使我们能够更好地将深部岩石圈/地壳过程（如岩浆活动和变形/流动）与地表过程联系起来，从而提供数据来测试大盆地岩石圈从缩短到伸展过渡的一系列想法和假设。我们对美国西部科迪勒拉山脉和落基山脉的地质知识构成了了解其广泛自然资源的基础，然而，这条山脉带的历史在许多方面仍然存在高度争议和争议。其中之一是我们对大陆地壳拉伸或伸展过程中形成的断层系统的概念理解（例如今天在盆地和山脉省发生的）。尽管这种断层系统对大陆和近海盆地的地下水和碳氢化合物等自然资源的勘探很重要，但它们的几何形状如何随着时间的推移而演变尚无共识。尽管这些问题对矿产资源勘探、热液能源、地震和火山灾害具有重要意义，但我们也不完全了解地表断裂伸展断层与深部岩浆活动、加热和地壳固态韧性流动等过程之间的联系。我们的研究目标是提供一个更全面的数据集，提供从地壳深部到地表断裂、火山喷发和沉积盆地事件的辐射定年，以了解科迪勒拉从板块构造收敛和缩短到分裂和伸展的时间跨度内深部地球过程与地表事件之间的时间限制联系。本项目将为3名博士研究生和1名硕士研究生的实地和实验室工作提供部分支持，为未来地球科学家的专业培养做出贡献。该项目为获得斯坦福大学本科生研究资金提供了杠杆作用。将向公众提供从大盆地国家公园到克恩山脉的1:6 25 500地质图数据汇编。这张地图将激发新的研究，并有利于该地区地质学实地课程和实地考察的教学。

The geologic history of the western U. S. Cordilleran is complex and an increasing number of questions have been raised about its deep crustal architecture. The most debated question is how its geology was shaped during the transition from plate convergence and crustal shortening in the Mesozoic to divergence and extension in the Cenozoic. Across today's Basin and Range Province, this transition period is characterized by shallow-slab subduction and the shut-off of arc magmatism ~ 70-50 m.y. ago followed by one of the biggest volcanic eruption events in its history, ~ 45-20 m.y. ago, setting the stage for Miocene Basin and Range faulting. This research focuses on placing better absolute ages on events occurring during this transition period across the central part of the Basin and Range province (east-central Nevada and adjacent Utah) in order to address current controversies about this history and produce a more holistic whole-crust model for this time-span. A multidisciplinary and comprehensive approach will mesh: 1. A pioneering effort to detail the U-Pb radiometric ages, trace element and isotopic geochemistry of xenocrystic/inherited zircon populations in magmatic rocks that span the transition from shortening to extension, revealing the temperature-time history of the deep crust 2. Structural/ microstructural studies coupled with petrology, geochronology and thermochronology of key rock transects that link inferred deep levels of the crust to near surface levels in the Snake Range metamorphic core complex- a locality where deformation and cooling histories figure prominently in the debate between very thick versus thinner crust and its role in crustal flow and collapse during the transition period. 3. The time-space evolution of sedimentary basins whose history provides a robust, definitive set of constraints for evolving landforms, their relation to volcanic eruptins, and the onset of fault uplift of the deeper rocks of core complexes. This comprehensive approach will allow us to better link deep lithospheric/crustal processes such as magmatism and deformation/flow to surface processes and thus provide data to test a range of ideas and hypotheses about the lithospheric evolution of the Great Basin as it transitioned from shortening to extension. Our geologic knowledge of the Cordillera and Rocky Mountains of the western U.S. forms the foundation for understanding its broad spectrum of natural resources, yet there are many aspects of the history of this mountain belt that are still highly debated and controversial. One of these is our conceptual understanding of fault systems formed during stretching or extension of continental crust (such as is happening today across the Basin and Range province). Despite the importance of such fault systems to the exploration of natural resources such as groundwater and hydrocarbons in continental and offshore basins, there is no consensus on how their geometries evolve through time. We also don't fully understand how surface-breaking extensional faults are linked to processes in the deep earth such as magmatic activity, heating and solid-state ductile flow of the crust, despite the importance of these questions to mineral resource exploration, hydrothermal energy sources, earthquake and volcanic hazards. Our research goals are to provide a more comprehensive data set that provides radiometric dating of events from the deep crust to surface breaking faults, volcanic eruption and sedimentary basins in order to understand the time-constrained links between deep earth processes and surface events during a time span where the Cordillera transitioned from plate tectonic convergence and shortening to divergence and extension from ~ 80 Ma to 20 Ma ago. This project will provide partial support for field and laboratory work of 3 Ph.D. and one M.S. student(s) contributing to professional training of future earth scientists. The project provides leverage to obtain funding for undergraduate research from Stanford. Compilation of geologic map data at 1:62,500 spanning the Great Basin National Park to the Kern Mountains will be made available to the general public. This map will stimulate new research and benefit teaching of geology field classes and field trips in this region.