Present-day lithosphere structure underneath the Tibetan Plateau inferred from potential fields: Influence of mantle dynamics on the topographic evolution

The Tibetan Plateau is the product of crustal thickening caused by collision between India and Asia. Plate tectonic reconstructions suggest continuous northward movement of the Indian plate relative to stable Eurasia at nearly 50 mm/yr for the last 50 My. The plateau is now at ~5 km elevation with steep topographic gradients across the southern and northern margins. These gradients are also associated with large lateral variations in geoid and gravity anomalies. Uplift late in the tectonic evolution of the plateau, the widespread extension, and the associated magmatism have been attributed to removal of the lower part of lithospheric mantle and its replacement by hotter and lighter asthenosphere. Here we present a two-dimensional lithospheric thermal and density model of the present day structure and numerical modeling of the evolution of the Tibetan Plateau. The two-dimensional lithospheric model is along a transect from the Indian plate to Asia, crossing the Himalaya front and the Tibetan Plateau. The model is based on the assumption of local isostatic equilibrium, and is constrained by the topography, gravity and geoid anomalies and by thermal data within the crust. Our results suggest that the height of the Tibetan Plateau is compensated by thick crust in the south and by hot upper mantle to the north. The Tibetan Plateau as a whole cannot be supported isostatically only by thickened crust; a thin and hot lithosphere beneath the northern Plateau is required to explain the high topography, gravity, geoid and crustal temperatures. We also investigate numerically the long-term (50 My) evolution of crustal and lithospheric thickness, thermal structure, topography, and strain-rate of the Tibetan plateau through time, using a planform viscous approach. This suggests that lithospheric mantle must have been removed from beneath Tibet, and that the crust must have been warmed and weakened by an increase of radiogenic heat production at depth due to crustal thickening.