Collaborative Research: How does it end? Exploring thrust terminations of an intra-continental strike-slip fault, north Tibet

板块构造理论认为内部刚性的构造板块沿着沿着狭窄的板块边界相互作用。然而，变形往往分布在大陆的内部，例如在喜马拉雅山带东北的亚洲大陆，在距离印度和欧亚板块边界一千多公里的地方发生了重大的断层和褶皱。该地区一些最大的特征是东西走向的走滑断层，如藏北的海原断层。本计画调查海原断层的西端，以确定在山带内部，变形如何由走滑断层运动转变为褶皱和逆冲断层运动。此外，像海原断层这样的构造是亚洲大陆人口密集地区的主要地震危险源。因此，约束的风格，规模和变形率沿着这些走滑断层的长度将有助于未来的灾害和风险评估。该项目的其他社会相关影响包括：支持早期职业教师建立具有全球竞争力的研究计划;培训一名博士生并指导两名科学，技术，工程和数学（STEM）学科的本科生;与研究人员和机构的国际合作;以及在社区参与活动中的外展活动，重点是地震灾害。该项目还支持开发一个可供公众访问的现代化地质测绘网站，该网站提供有关数字平板野外测绘和数字高程模型构建的技术和信息，包括将地图数据纳入开放式在线档案的方法。喜马拉雅-青藏造山带是新生代印度-亚洲板块汇聚的结果，造山带内部最大的构造是大型走滑断层。因此，西藏是一个理想的试验场，以确定如何在碰撞造山带的走滑断层调节和重新分配应变。本研究探讨了藏北北方海原左滑断裂的西端，在此走滑断裂突然转变为逆冲断裂。具体而言，地质基岩和新构造测绘的结合，使用运动恢复结构（SfM）方法构建数字高程模型（DEM），表面年龄测定（即，利用光学释光和放射性碳）和低温热年代学（1）限制了海原断裂西段沿着第四纪的滑动速率，（2）系统地记录了走滑变形如何向中祁连山逆冲带的范围边界逆冲断层系统转化。利用海原断裂西端运动学的野外观测资料，对喜马拉雅-青藏造山带板块会聚-正走滑断裂模式进行了检验，包括（1）顺时针旋转模式、（2）挤压模式和（3）应变传递模式。通过研究海原断层获得的见解可以应用于其他大陆内部变形带。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Plate tectonic theory suggests that internally rigid tectonic plates interact with one another along narrow plate boundaries. However, deformation is often distributed across the interior of continents, such as in the Asian continent northeast of the Himalayan mountain belt, where significant faulting and folding occurs more than a thousand kilometers from the boundary between the Indian and Eurasian plates. Some of the largest features in the region are east-west oriented strike-slip faults, such as the Haiyuan fault in north Tibet. This project investigates the western termination of the Haiyuan fault to determine how deformation changes from strike-slip fault motion to folding and thrust faulting within the interior of the mountain belt. Furthermore, structures like the Haiyuan fault are sources of major seismic hazards for densely-populated regions within the Asian continent. Thus, constraining the style, magnitude, and rate of deformation along the length of these strike-slip faults will aid in future hazard and risk assessment. Other societally relevant impacts of this project include: support of early-career faculty to establish globally competitive research programs; training a PhD student and mentoring two undergraduates in a science, technology, engineering and mathematics (STEM) discipline; international collaboration with researchers and institutions; and outreach at community engagement events with a focus on earthquake hazards. The project also supports the development of a modern publicly-accessible geologic mapping website that features techniques and information about digital tablet-based field mapping and digital elevation model (DEM) construction, including methods of incorporating map data into open-access online archives.The intra-continental response to edge-driven plate boundary conditions is a central topic in continental tectonics. The Himalayan-Tibetan orogen results from progressive Cenozoic India-Asia convergence, and the largest structures within the interior of this orogen are large strike-slip faults. Therefore, Tibet is an ideal testing ground to determine how strike-slip faulting accommodates and redistributes strain in a collisional orogen. This multidisciplinary investigation explores the western termination of the left-slip Haiyuan fault within northern Tibet, where strike-slip faulting abruptly transitions to thrust faulting. Specifically, a combination of geologic bedrock and neotectonics mapping, construction of digital elevation models (DEMs) using structure-from-motion (SfM) methods, surface-age dating (i.e., optically stimulated luminescence and radiocarbon), and low-temperature thermochronology are employed to (1) constrain Quaternary slip rates along the western Haiyuan fault segments, and (2) systematically document how strike-slip deformation transfers to a range-bounding, thrust-fault system in the central Qilian Shan thrust belt. Field observations of the kinematics of the western termination of the Haiyuan fault are used to test models for plate-convergence-normal strike-slip faulting in the Himalayan-Tibetan orogen, including (1) clockwise-fault rotation, (2) extrusion-fault models, and (3) strain transfer models. Insights gained from studying the Haiyuan fault can be applied to other zones of intra-continental deformation.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.