Two Stages of Accelerated Exhumation in the Middle Reach of the Yarlung River, Southern Tibet Since the Mid‐Miocene

Abstract

AbstractClimate change and tectonic activity through erosion control Earth’s topography, much of which is shaped by river incision. The Yarlung River has dissected the Indian‐Asian Collision Zone, and is one of the Earth’s largest rivers. However, its erosion rate history and how it interacts with regional tectonics remain ambiguous. Here, we apply low‐temperature thermochronometry and thermal‐kinematic models for bedrock samples from the Yarlung River. Our analysis reveals two stages of relatively fast exhumation occurred in different parts of the middle reach of the Yarlung River followed by remarkedly slow exhumation rate. First, a mid‐Miocene period (15–9 Ma) of rapid exhumation occurred along much of the Yarlung River, including within wide portions of the valley and its tributaries. This period of rapid exhumation coincides with the stage of high precipitation rates recorded in the Asian marginal basins and the timing of the east‐west extensional faults. In combination with extensional faults, the enhanced precipitation due to the onset of Asian monsoon would increase river discharge and thus accelerate mid‐Miocene exhumation rates. Second, a Pliocene‐Pleistocene (5–2 Ma) period of accelerated exhumation limited to gorges occurred in response to north‐south normal faulting, implying local tectonics as a first‐order control. Our results highlight roles of climatic and tectonic processes in shaping fluvial topography and how these change with time.