BIRTH OF THE MEKONG RIVER REVEALS TOP-DOWN FORCING FOR FLUVIAL INCISION

The complex nature of the coupling between atmospheric, surficial, and deeper Earth processes in the development of orogens and shaping Earth’s landscape is one of the most fundamental challenges in Earth sciences. Deeply incised gorges in upland regions have the potential to reveal the nature of this coupling. Based on low-temperature thermochronology, we show that a phase of rapid >700 m downward incision in the lower reaches of the Mekong River draining the Southeastern Tibetan Plateau occurred during the middle Miocene. Paleoaltimetry data demonstrate the current elevation of the southeastern Tibetan Plateau was reached by the late Eocene, while the middle Miocene is characterized by extreme warming and intensified East Asian summer monsoon. In the absence of any obvious tectonic contribution, this provides the first unambiguous evidence for warm climatic control on km-scale fluvial incision in the Tibetan Plateau and demonstrates the importance of the monsoon in shaping Earth’s surface.