Abstract
Three end member models of how the Tibetan Plateau reached its current areal extent and elevation are (1) continuous shortening of soft lithospheric plate of the entire plateau, 2) localized shear and successive extrusion of rigid plates, and 3) a time-variant combination of these two tectonic styles. The past 20 years of studies of the slip history of the Altyn Tagh fault and Alxa-East Mongolia fault, structural geology and elevation history of the entire Tibetan Plateau, and magnetic stratigraphy of northern Tibet support the latter. Since the collision between India and Eurasia nearly equal 50Ma ago, the tectonic deformation in the Tibetan Plateau likely has occurred in two contrasting phases. Before mid-Miocene, the convergence between India and Eurasia was accommodated mainly through northeastward extrusion of rigid tectonic plates along major strike-slip faults. As a major plate boundary, the Altyn Tagh fault, together with the Alxa-East Mongolia fault, had experienced rapid slip and accumulated most or all of its total displacement during this phase. During the mid-Miocene, the Tibetan lithosphere lost its rigidity due to thermal weakening of its lithospheric mantle and the continued convergence between India and Eurasia was subsequently accommodated by continuous shortening of softened Tibetan lithosphere. During this phase, slip along the Altyn Tagh fault and Alxa-East Mongolia fault slowed and ceased respectively, block rotation stopped and the Tibetan Plateau uniformly and rapidly exhumed. The change in deformation behaviour in the northern Tibetan Plateau was accompanied by several notable changes in global tectonics: mid-Miocene reorganization of the NW Pacific margin, mid-Miocene buckling of the Indian Ocean lithosphere, and widespread mid-Miocene inversion from the South China Sea to NW Australia, all suggesting increased confinement along all of the southern and eastern Eurasia plate margins.