NUMERICAL MODELING AT INTERMEDIATE SCALES OF COUPLING BETWEEN EROSION AND TECTONICS, SUTLEJ RIVER, NW INDIA

Along the Himalayan Front, areas subjected to concentrated precipitation or enhanced river erosion coincide with rapid exhumation as indicated by young mineral cooling ages. While numerical modeling of the Himalayan syntaxes has shown that tectonic and fluvial erosion processes are coupled through a positive feedback, we focus on orographic precipitation and its impact on focussed exhumation. Along the southern Himalayan front (SHF), in the area of the Sutlej River (NW-India) active deformation of the orogen coincides with high monsoonal precipitation (c. 2.5 m/yr), high relief, steep river gradients and slope angles that predispose these rocks to effective mass removal. Field evidence and Ar/Ar and Apatite fission track dating suggest a strong interaction between rapid erosion and exhumation concentrated in a 50 km-wide sector of the Himalayan orogen. In addition, processes operating on decadal to millenial time scales involving extreme monsoonal events and their control on localized erosion and sediment evacuation characterize these areas. But how this inhomogeneous distribution of precipitation affects mountain building processes of the Himalayan range is still controversial.

We investigate, using three-dimensional mechanical models, the interplay between tectonic forcing, topographic stresses and climatically driven denudation of material from the Sutlej Valley. Our models are aimed at quantifying the spatial and temporal scales of the coupling between erosion and tectonics. We define the erosion conditions required to affect the tectonic signal by the removal of mass, weakening due to the development of high relief (TSI) and weakening as a result of the upward advection of isotherms.