Coupled influence of tectonics and surface processes on the drainage evolution in collisional orogens: an example from the three rivers region in Southeast Tibet.

The three river region (TRR, Salween, Mekong, and Yangtze Rivers) in southeast Tibet provides an example of drainage evolution in active orogenic system. Over decades of investigations based on geomorphic evidence analysis, or landscape evolution modeling, the main factor resulting in the unusual drainage patterns in this area remains controversial. Some studies argued that the horizontal tectonic deformation has brought the previous rivers to be nearly parallel in extraordinary close space. In contrast, others suggested that can be explained by drainage reorganization, and the capture and reversal events merely appeal to the surface uplift.

Tectonics and surface processes integrate to shape the topography of fluvially conditioned mountain ranges, and important two-way feedbacks exist between them. The direct feedback through isostatic response is related to the vertical aspect of exhumation and surface uplift. Surface processes also alter the thermal and stress field in the lithosphere by redistributing significant volumes of materials, which further affect both horizontal and vertical components of tectonic displacement.

We study the drainage evolution in theTRR using a fully coupled 3-D model built by the UWGeodynamics module, which coupled the geodynamics code Underworld 2 with landscape evolution model code Badlands.