LATE CENOZOIC TECTONIC EVOLUTION OF THE EASTERN HIMALAYAN DRAINAGE SYSTEM: INTERPLAY BETWEEN RIFTING, UPLIFT, AND GLACIATION

How major rivers evolve during orogeny is a fundamental question in Earth Sciences. For example, mountain building can cause focused erosion that in turn may trigger thermal weakening and localized contraction, leading to positive feedback between erosion and uplift. One of the best places to address the coupled interactions among tectonics, climate change and surface processes is the active Himalayan orogen. There all these factors can be well quantified due to significantly larger and thus more readily detectable signals than most places on Earth. Field mapping coupled with sedimentologic observations, detrital zircon U-Pb and Hf isotopic provenance data, and thermochronology have been used to constrain the evolution of the Himalayan drainage system throughout the Late Cenozoic. Available results indicate that interactions between north-trending Tibetan rifts and Himalayan uplift modulated by climate and surface-process events influenced when and how the east-flowing Yalu River (Yarlung Tsangpo) was captured by transverse drainage systems in the eastern Himalaya. Fieldwork in SE Tibet has revealed a sequence of valley-fill sediments distributed across the Yalu-Subansiri drainage divide. The valley fill, likely representing the paleo-Yalu-Subansiri river sediments, is located in the north-trending Cona-Zedong rift zone and contains thick (>150 m locally) moraine deposits. These associations suggest that the capture event of the Yalu by the Subansiri was controlled by rifting and occurred during major glacier advances. We hypothesize that a climate event marked by protracted glacier advances triggered the formation of a rift dam in SE Tibet via strongly coupled tectonic-climate processes. This dam blocked and subsequently diverted the east-flowing Yalu River into the south-flowing Subansiri River and ultimately into Late Miocene-Pliocene foreland-basin sediments of the eastern Himalaya. Accelerated Himalayan uplift, possibly energized by the capture event, eventually forced the Yalu to return to its original course.