How did the convergence history influence the evolution of Tibet and the Himalayas?

Abstract:

Convergence between India and Eurasia is characterised by velocities of > 10 cm yr^-1 at collision to current velocities of ~5 cm yr^-1, of which ~2cm yr^-1 are accommodated at the orogens' front. This has resulted in three primary tectonic domains: the thickened crust of Tibetan Plateau (TP), the metamorphic Greater Himalayan Sequence (GHS) and the Himalayan Fold and Thrust (FAT) belt in the Lesser and Sub-Himalaya. We use a numerical model to simulate the collisional history to better understand the controls on the evolution of the region, highlighting 4 key phases. Phase 1 (50 - 44 Ma) is characterised by high velocities that result in crustal scale faulting and developing of a proto-wedge. In phase 2 (44 - 32 Ma), the orogenic wedge reorganises and convergence is accommodated through deep burial of crust and its exhumation along a localised channel flow at the front of the wedge. In the upper plate, the Indian crust underthrusts Asian crust to form a wide plateau. As convergence slows the burial rate decreases, phase 3 (32 - 25 Ma) allowing temperature increase at the root of the orogeny. Subsequently, phase 3 occurs (32-25 Ma), with the change in kinematics favouring the emplacement of hotter, weaker deep crust in a shallow dome. Further slowing in phase 4 (25 - 0 Ma) allows the orogenic root to continue warming. The increasing geotherm causes a shallowing of the thermally controlled brittle-ductile transition, which results in convergence being accommodated by a fold and thrust belt (FAT) at the wedge front, while deep burial and exhumation ceases. When compared to the Himalaya-Tibet collisional zone, the phases, duration and deformation styles are remarkably similar, showing that the complexities of this collisional zone are best explained by the conditions imposed by the plate convergence.