Using structural fabrics and thermochronology to document extensional footwall rotation--Insights from the tilted Miocene Searchlight pluton, NV

内华达州的盆地和山脉景观是由过去几千万年的地壳伸展形成的。这种延伸受到广泛的断层作用和同步岩浆作用的影响，这产生了危险的地震，导致了许多岩体（即，结晶岩浆体）与有价值的矿床有关，并有助于提供全州地热能潜力的高地壳温度。在这项研究中，主要研究人员正在调查地壳拉伸的类型和幅度以及断层与岩体侵位之间的关系。特别是，不同类型的地壳变形影响了初始热岩体的冷却和区域地热梯度。地壳冷却的速率直接影响着地壳的伸展方式、整体强度和未来地震的潜在分布。这项工作的目标是通过调查一个倾斜的岩体，提供了一个独特的暴露的垂直组成和古热剖面的地壳，以重建构造和热历史的这一部分的盆地和山脉地壳。这项工作的影响，了解构造和岩浆演化的盆地和山脉，地壳强度和深度的地方地震，构造和岩浆活动之间的联系，高地壳温度和地热能。除了该项目的研究目标外，该奖项的重要社会成果包括支持在重要的科学，技术，工程和数学（STEM）学科中培养研究生。 它还推动了两名早期职业调查人员的研究工作。该项目的参与者还参与了内华达州大学里诺分校的公共外联项目，从而为提高公众科学素养和公众参与STEM做出了贡献。这些努力包括通过外联活动向公众传播尖端研究成果，其中包括在内华达州矿业和地质局举办的地球科学周年度活动。开发数字测绘技术，并通过虚拟现实测绘为可能有身体残疾的学生实施适应性教育，从而促进残疾人充分参与STEM教育。最后，这项研究呼应了最近的社区对未来的挑战和机遇，在构造研究和促进社区的努力，以推进知识的构造地质和tecticsThe项目量化构造和热历史的中新世探照灯岩体在科罗拉多伸展走廊附近的拉斯维加斯，以更好地了解伸展断层过程中的侵位和随后的冷却。PI表征了岩体内的结构和组构，以检验“岩体在简单剪切伸展过程中经历了类似流动的下盘旋转”的假设。“这种伸展机制通过限制观察到的结构的性质，岩体和围岩内的变形运动学以及通过综合结构，数值模拟和热年代学研究的冷却历史来测试具体的预测。工作的假设是，在简单剪切伸展的下盘旋转是一个更有效的地壳冷却机制比纯剪切模式的扩展，因为旋转平流的高温部分的岩体向地球表面冷却。快速冷却增加了上地壳的流变强度，并可以作为一个负反馈，停止进一步快速扩展通过脆性断层。在这项研究中使用了各种补充方法，包括（1）数字野外测绘，以表征Searchlight岩体内的组构图案、局部剪切方向和接触，（2）通过电子背散射衍射进行高级显微镜研究，以确定组构的性质、温度、风格和运动学，（3）最先进的计算模拟，以构建和完善分析/数值热-下盘倾斜和相关地壳冷却的运动学模型，将通过热年代学预测冷却历史，（4）磷灰石和锆石（U-Th）/He热年代学研究，以确定冷却历史。该项目揭示了构造/构造过程，将地壳的瞬态热和流变演化与从颗粒到露头到区域尺度的变形机制联系起来。热年代学和模拟研究探讨了拉张过程中的热演化及其对地壳流变学的影响。导出的冷却速率，连同详细的结构分析，约束盆地和山脉的地质应变率和新的稳健的估计中新世的时间和速度在科罗拉多伸展走廊。这项研究还揭示了地表热通量，矿石形成和热液系统之间的联系。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

The Basin and Range landscape of Nevada has been shaped by crustal extension over the past tens of millions of years. This extension is accommodated by widespread faulting and synchronous magmatism, which has generated hazardous earthquakes, resulted in many plutons (i.e., crystalized magma bodies) associated with valuable ore deposits, and contributed to the high crustal temperatures that provide geothermal energy potential across the state. In this study, the principal investigators are investigating the styles and magnitudes of the crustal stretching and the relationship between faulting and pluton emplacement. In particular, different styles of crustal deformation affect the cooling of initially hot plutons and the regional geothermal gradient. The rate of crustal cooling directly impacts the extensional style, the overall strength of the crust, and the potential distribution of future earthquakes. The goal of this work is to reconstruct the tectonic and thermal histories of this part of the Basin and Range crust by investigating a tilted pluton that provides a unique exposure of the vertical compositional and paleo-thermal profile of the crust. This work has implications for understanding the tectonic and magmatic evolution of the Basin and Range, the crustal strength and depth of local earthquakes, and the linkage between tectonic and magmatic activities to high crustal temperatures and geothermal energy. In addition to the research goals of the project, important societal outcomes of the award including supporting the training of a graduate student in an important science, technology, engineering and mathematics (STEM) discipline. It is also advancing the research efforts of two early-career investigators. Participants of this project are also involved in public outreach programs at the University of Nevada, Reno thereby contributing to increased public science literacy and public engagement with STEM. These efforts include dissemination of cutting-edge research results with the public via outreach events including the annual Earth Science Week event at the Nevada Bureau of Mines and Geology. The development of digital mapping techniques, and the implementation of adaptive education via virtual reality mapping for students who may have physical disabilities that impair traditional field techniques and education, thereby contributing to the full participation of persons with disabilities in STEM education. Finally, this research echoes the recent community vision on the future challenges and opportunities in tectonics research and promotes the community effort to advance the knowledge of structural geology and tectonicsThe project quantifies tectonic and thermal histories during the emplacement and subsequent cooling of the Miocene Searchlight pluton in the Colorado extensional corridor near Las Vegas to better understand the extensional faulting process. The PIs characterize structures and fabrics within the pluton to test the hypothesis that "the pluton experienced flow-like footwall rotation during simple-shear extension." This extensional mechanism makes specific predictions to be tested by constraining the nature of the observed fabrics, deformation kinematics within the pluton and wallrock, and cooling history through an integrated structural, numerical modeling, and thermochronology study. The working hypothesis is that the footwall rotation during simple-shear extension is a more effective crustal cooling mechanism than pure-shear modes of extension because rotation advects the hotter parts of the pluton toward the Earth's surface to cool. Rapid cooling increases the rheological strength of the upper crust and can act as a negative feedback to cease further rapid extension via brittle faulting. Various complementary methods are used in this study including (1) digital field mapping to characterize the fabric patterns, local shear sense, and contacts within the Searchlight pluton, (2) advanced microscopic study by electron backscatter diffraction to determine the nature, temperature, style, and kinematics of fabrics, (3) state-in-art computational simulations to construct and refine analytical/numerical thermo-kinematic models of footwall tilting and associated crustal cooling that will predict cooling histories to be tested via thermochronology, and (4) apatite and zircon (U-Th)/He thermochronometry to constrain the cooling history. This project sheds light on structural/tectonic processes linking transient thermal and rheological evolution of the crust with deformation mechanisms from grain to outcrop to regional scales. Thermochronology and modeling explore the thermal evolution during the extensional process and impacts on crustal rheology. The derived cooling rates, together with detailed structural analysis, constrain the geologic strain rates in the Basin and Range and new robust estimates for the timing and rates of Miocene extension in the Colorado extensional corridor. This study also sheds light on linkages between surface heat flux, ore formation, and hydrothermal systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.