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

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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 along the Himalayan mountain belt, where significant faulting and folding occurs thousands of kilometers from the boundaries between the Indian and Pacific 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.