Modeling mountain building, numerical trade off between erosion law and crustal rheology

Coupling between erosion and tectonics are thought to play a determinant role in mountains evolution. Here, we investigate the interplay in this coupling between the assumed erosion law and the crustal rhe-ology at the margin of a collisional plateau, like the Himalaya of central Nepal. Lithospheric deformation is calculated over a time scale of 100 kyr by a two-dimensional finite elements model that incorporates the rheological layering of the crust and the main features of the convergence across the range including shortening rate and geometry of the Main Himalayan Thrust fault. For the upper boundary condition, several surface processes were tested: a linear diffusion model and a 1D1/2 integrative model including fluvial incision along the fluvial network and hillslope erosion by landsliding. Model results and their sensitivity to the chosen combinations of erosion law and crustal properties are discussed in light of the constraining geologic and ge-omorphologic observations (topography, river elevation, denudation and flu-vial incision rates). In contrast with the conclusions of Cattin and Avouac [2000] where a compliant, quartz-rich crustal rheology and diffusion law were required, we rather propose to use a composite quartz-diabase rheology for the crust associated with fluvial incision to account for erosion and elevation profiles across the Himalaya of central Nepal. More generally, it is proposed that, because of the interplay between the dominant denudation conditions and rheology of the crust, well documented erosion rates and processes can provide significant constrains on crustal properties within an active oro-gen.