ENVIRONNEMENTALE

Deformation syles during continental collision: 3D numerical simulations and application to the India-Asia collision

Our understanding of the tectonic evolution of the India-Asia collision is still incomplete and many open questions remain concerning the deformation style of crustal thickening causing the outstandingly high elevation of the Tibetan Plateau. Different models have been suggested that explain crustal thickening by, for example, (1) homogeneous, continuous ductile thickening using thin-sheet models, (2) heterogeneous, ductile deformation including folding, (3) discrete movement along thrusts developing crustal wedges, and (4) lateral crustal flow due to pressure gradients resulting from topography. Yet, most existing models are not fully 3D and assume a certain deformation style a priori, which makes it difficult to judge the relative importance of this deformation style for the formation of the Tibetan Plateau. We therefore apply a fully 3D numerical finite element model to the India-Asia collision in order to compare numerically calculated velocity fields to measured surface GPS-velocities and shear wave splitting data of the mantle. The model geometry is set up using available geophysical data. We the perform instantaneous indentation of India into Asia to represent today's state of the continent-continent collision. The impact of carious rheological profiles on the velocity field with surface GPS-velocities and at depth withz shear wave splitting data of the area, in order to deduce the rheology, material parameters and the deformation style of the Indian and Asian lithospheres.