Collaborative Research: What Created the Southern Tibetan Plateau Drainage Divide? Integrated Tectonic and Geomorphic Investigation of the Gangdese Range and Yarlung River

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Collisional motions between tectonic plates deform the Earth's crust, forming mountain belts over millions of years. This process is most visible along the boundaries between tectonic plates, but also occurs further away from plate boundaries, where more subtle features reflect deeper-seated tectonic movements. This project focuses on the Gangdese Mountains in southern Tibet, which host some of the highest mountains of the Tibetan Plateau. These mountains are located 200 kilometers north of the high peaks of the Himalayas, but are actively rising due to deep-seated faulting related to collision between the Indian and Asian tectonic plates. This range forms the boundary between the low-relief, relatively flat interior of the Tibetan Plateau that retains all precipitation in lakes, and the higher-relief region to the south that is drained by the Yarlung-Siang-Brahmaputra river. By mapping the geologic structures, determining when and at what rate rocks were exposed at the surface, and comparing these data to simulations of erosion due to precipitation and river incision, the project investigators will determine the details of the deep-seated tectonic motions and how these motions affected the landscape of the Tibetan Plateau and one of the largest river systems in Asia. Broader impacts of this project will include the development of teaching modules based on this research, the preparation of three PhD students and one postdoctoral researcher to join the skilled scientific workforce, and outreach to the public through museum-hosted instructional modules and public research presentations. This research seeks to understand how and to what extent Miocene to Recent tectonics affected the landscape and river systems of the southern Tibetan Plateau. The project will test the hypothesis that a major crustal ramp or duplex beneath the Gangdese Mountains drove rock uplift along the southern boundary of the Plateau, in the interior of the Himalayan orogenic belt, since at least Miocene time. Research will focus on whether rock uplift outpaced erosion and established the drainage divide that currently separates the expansive internally-drained region from the Yarlung-Siang-Brahmaputra river system to the south. To address this hypothesis and other alternative hypotheses, the researchers will conduct an integrated study involving field-focused structural geology, thermochronology, landscape evolution modeling, and detrital cosmogenic radionuclide dating. The hypotheses provide a set of testable predictions for the geometry of rock exposures and the history of deformation, timing and rates of rock cooling, expected landscape evolution in response to various tectonic and/or climatic drivers, and millennial-scale erosion rates for catchment basins. If a tectonic driver for establishment of the southern drainage boundary is supported by the data, then tectonics is also implicated in the evolution of the Yarlung-Siang-Brahmaputra River system, one of the largest in the world. This research will advance our collective understanding of how mountain belts and plateaus form in response to tectonics, how mountain landscapes evolve and respond to variable tectonic influences, and how major river systems develop during million-year to millennial timescales.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.