Collaborative research RUI: Timing of slip along the Sierra Nevada frontal fault zone, California: A thermochronologic study

加州的南部内华达州山脉的东侧形成了一个令人印象深刻的地形悬崖，与美国相连的一些最高海拔的山峰。沿着欧文斯谷的陡坡在结构上受活动的塞拉内华达州前缘断层带控制。本研究项目的重点是太平洋-北美板块相互作用过程与延伸的盆地和山脉相交的区域。因此，内华达州山脉的东部边缘长期以来一直受到构造学界的关注，该地区断层和隆起的时间仍在争论之中。本研究项目的重点是南部的山脉内华达州锋面断裂带将揭示的长期结构演变的正断层界定令人印象深刻的山脉内华达州山前，并解决几个基本问题：什么时候形成的范围前？内华达州山脉前缘断层带是新生代晚期一个或两个不同的正断层滑动事件的产物吗？在这些正常滑动的事件中，南部的内华达州山脉是失去了还是增加了海拔？该项目通过以下方式推进预期的社会成果：（a）通过本科生，包括少数民族学生和研究生参与研究的各个方面，培训下一代科学家;（B）通过研究生和本科生培训，培养一支多样化、具有全球竞争力的STEM工作队伍;（d）在Sierra内华达州为STEP的本科新生和转学生制定一项基于实地的推广计划，以提高科学素养（科学人才扩展计划，这是集中在传统上代表性不足的学生的科学培训）。本研究项目将测试两个主要假设：（1）南部Sierra内华达州前缘断裂带记录了两幕晚新生代正断层滑动;南部的内华达州山脉在第一次正常滑动期间要么失去要么获得海拔，在第二次正常滑动期间获得海拔简整合新的实地研究（地质测绘，结构和运动学）和低温热年代学（磷灰石裂变径迹，（U-Th）/He和4 He/3 He），与已发表的地质数据，在正向和反向热动力景观演化建模将被用来测试这些假设。根据模型结果对晚新生代正滑和地表隆起历史的时间数据进行检查，将允许对不同地球动力学过程的有效性进行评估（例如，板片窗的发展，太平洋-北美板块运动相对速率的增加，挠曲-均衡模型，软流圈置换下沉的致密岩石圈）假定为驱动沿内华达州山脉前缘断层带的沿着断层和内华达州山脉平均地表高程的变化。这项研究的动机是长期存在的分歧，无论是内华达州山脉记录在中生代晚期的隆起，然后在整个新生代没有变化或海拔下降，或在中生代晚期的隆起，然后在新生代中期的海拔下降，然后在新生代晚期的第二个脉冲的隆起。在这项研究中获得的数据-正常断层滑动运动学，滑动历史和沿着内华达州前缘断层带的滑动速率-将与已发表的侵蚀速率，热压测量和其他地质约束的结果相结合，形成正向和反向热动力景观演化模型，以表征内华达州南部的正常断层滑动和新生代晚期隆起历史，并评估所提出的驱动正断层滑动和隆升的地球动力学过程的合理性。这项研究是第一个应用低-温度热计时法研究直接到整个内华达州山脉前缘断层带悬崖，并使用这种调查工具的组合，以表征晚新生代沿着内华达州山脉前缘断层带的滑动历史和内华达州山脉的隆升历史。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的知识产权评估的支持优点和更广泛的影响审查标准。

The eastern flank of the southern Sierra Nevada, California, forms an impressive topographic escarpment with some of the highest elevation peaks in the conterminous United States. The escarpment along Owens Valley is structurally controlled by the active Sierra Nevada frontal fault zone. This research project focuses this zone where Pacific-North America plate interaction processes intersect with the extending Basin and Range. Thus, the eastern margin of the Sierra Nevada has been of long-standing interest to the tectonics community and the timing of faulting and uplift of the region remains under debate. This research project focused on the southern Sierra Nevada frontal fault zone will shed light on the long-term structural evolution of the normal faults bounding the impressive Sierra Nevada mountain front and address several fundamental questions: When did the range front form? Is the Sierra Nevada frontal fault zone the product of a single or two distinct episodes of late Cenozoic normal fault slip? And did the southern Sierra Nevada lose or gain elevation during these episodes of normal slip? The project advances desired societal outcomes by: (a) training the next generation of scientists via involvement of undergraduates, including minority students, and graduate students in all aspects of the research; (b) developing a diverse, globally competitive STEM workforce through graduate and undergraduate student training; (c) fostering international collaboration and (d) enhancing scientific literacy by developing a field-based outreach program in the Sierra Nevada for undergraduate freshman and transfer STEP students (Science Talent Expansion Program, which is centered on scientific training of traditionally underrepresented students).This research project will test two primary hypotheses: (1) the southern Sierra Nevada frontal fault zone records two episodes of late Cenozoic normal fault slip and (2) the southern Sierra Nevada either lost or gained elevation during the first episode of normal slip and gained elevation during the second episode of normal slip. Integration of new field studies (geologic mapping, structural, and kinematic) and low-temperature thermochronology (apatite fission track, (U-Th)/He, and 4He/3He), with published geologic data, in forward and inverse thermokinematic-landscape evolution modeling will be used to test these hypotheses. Examination of data on the timing of late Cenozoic normal slip and the surface uplift histories in light of model results will allow assessment of the validity of different geodynamic processes (e.g. development of a slab window, increase in relative rate of Pacific-North America plate motion, a flexural-isostatic model, and replacement of foundering dense lithosphere with asthenosphere) postulated as driving both faulting along the Sierra Nevada frontal fault zone and changes in mean surface elevation of the Sierra Nevada. This research is motivated by the long-standing disagreement whether the Sierra Nevada records uplift in the late Mesozoic followed by no change or a decrease in elevation throughout the Cenozoic, or uplift in the late Mesozoic followed by a decrease in elevation during the middle Cenozoic and then a second pulse of uplift in the late Cenozoic. Data acquired during this research - normal fault slip kinematics, slip histories, and slip rates along the Sierra Nevada frontal fault zone - will be combined with published results on erosion rates, thermobarometry, and other geologic constraints into forward and inverse thermokinematic-landscape evolution models to characterize the normal fault slip and late Cenozoic uplift histories of the southern Sierra Nevada, and to assess the soundness of proposed geodynamic processes driving normal fault slip and uplift. This research is the first to apply low-temperature thermochronometry studies directly to the entire Sierra Nevada frontal fault zone escarpment and to use this combination of investigative tools to characterize the late Cenozoic slip history along the Sierra Nevada frontal fault zone and uplift history of the Sierra Nevada.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.