Jurassic-Early Cretaceous Tectonism, Orogenesis, and Basin Formation in Nevada: An Integrated Test of Models for Growth of the U.S. Cordillera

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。这项研究旨在调查和解决美国西部科迪勒拉中生代地质演化中的一个重要争议。 中生代的过程，包括变形、变质、岩浆作用和沉积作用，将美国西部从一个主要的海洋省份转变为一个隆起的大陆陆块。 这些过程也创造了一个地壳结构，这对自然资源（包括石油、矿床、热液和地下水）的位置和性质至关重要，因此对理解具有相当重要的意义。 该项目所涉及的争议涉及两个主要问题：（1）中生代造山运动是发生在一个单一的长期事件中，始于160 Ma的内华达州西部，并在65 Ma期间向东传播到犹他州，还是该地区在两个不同且不相关的造山事件中发展（200-160 Ma，约120-65 Ma），被一个漫长的侵蚀期分开？ (2)在内华达州、犹他州和爱达荷州，160 Ma前的沉积盆地是由于不断增长的山脉的弯曲载荷而形成的，还是在没有山脉加载地壳的时候，这些盆地是通过其他机制形成的？本项目将通过对北方内华达州、西北部犹他州和东南部爱达荷州受变形、变质、岩浆作用和盆地形成影响的地区进行有针对性的研究，重点回答这些问题。 本文的主要目的和方法如下。 (1)为侏罗纪变形提供严格的年龄限制。 这将通过对构造前、构造同期和构造后火成岩进行锆石U-Pb定年来完成。 如果单相模式正确，变形时间应在晚侏罗世（160-145 Ma），如果两相模式正确，变形时间应在160 Ma以上。 (2)确定内华达州的构造和地层演化，其中关键关系已被描述和争议，目前没有共识。 其目标是建立一个详细的事件序列，可以直接链接到地质年代学和物源研究。 (3)利用碎屑锆石U-Pb定年技术，对侏罗系砂岩单元的物源进行了约束。 砂的来源提供了古地理学的信息。 如果单相模式是正确的，晚侏罗世沉积物应来自西部造山高地的侵蚀。 如果两相模型是正确的，这应该是正确的中侏罗世沉积物。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This research seeks to investigate and resolve an important controversy in the Mesozoic geologic evolution of the western U.S. Cordillera. Mesozoic processes, including deformation, metamorphism, magmatism, and sedimentation transformed the western U.S. from a largely marine province to an elevated continental landmass. These processes also created a crustal architecture that is critical to the location and character of natural resources (including oil, ore deposits, hydrothermal, and groundwater) and therefore of considerable importance to understand. The controversy addressed by this project concerns two major questions: (1) Did Mesozoic mountain-building occur in a single long-lived episode that started at 160 Ma in western Nevada and propagated eastward into Utah through 65 Ma, or did the region grow during two distinct and unrelated mountain-building episodes (200-160 Ma, and about 120-65 Ma) that were separated by a lengthy period of erosion? (2) Did pre-160 Ma sedimentary basins in Nevada, Utah and Idaho form in response to flexural loading by growing mountains, or did these basins form by other mechanisms during a time when there were no mountain loading the crust?This project will focus on answering these questions by targeted studies in localities affected by deformation, metamorphism, magmatism and basin formation in northern Nevada, NW Utah and SE Idaho. The main objectives and methods are as follows. (1) Generate tight age constraints for Jurassic deformation. This will be done by U-Pb zircon dating of pre-, syn- and post-tectonic igneous rocks. If the single phase model is correct, deformation should be Late Jurassic (about 160-145 Ma); if the two phase model is correct, deformation will be older than about 160 Ma. (2) Determine the structural and stratigraphic evolution of locations in Nevada where critical relations have been described and disputed, with no current consensus. The goal is to establish a detailed sequence of events that can be linked directly to geochronologic and provenance studies. (3) Constrain the provenance of Jurassic sandstone units by U-Pb dating of detrital zircons. Provenance of sands provides information about paleogeography. If the single phase model is correct, Late Jurassic sediments should be derived from erosion of orogenic highlands to the west. If the two phase model is correct, this should be true for Middle Jurassic sediments instead.