Lithospheric Evolution and Geodynamic Process of the Qinghai‐Tibet Plateau: An Inspiration from the Yadong‐Golmud‐Ejin Geoscience Transect

Abstract The Tibet Geoscience Transect (Yadong‐Golmud‐Ejin) has revealed the basic structures, tectonic evolution and geodynamic process of the lithosphere of the Qinghai‐Tibet plateau. The evidence of northward thrusting of the Indian plate beneath the Himalayans on the southern margin and to southward compression of the Alxa block on the northern margin has been found. They were the driving forces causing the plateau uplift. The plateau is a continent resulting from amalgamation of eight terranes. These terranes are separated by sutures or large‐scale faults, and different terranes have different lateral inhomogeneities and multi‐layered lithospheric structures. At depths of about 20–30 km of the crust in the interior of the plateau there commonly exists a low‐velocity layer. It is an uncoupled layer of the tectonic stress; above the layer, the upper crustal slices were thrust and overlapped each other and the rocks underwent brittle deformation, thus leading to shortening and thickening of the upper crust. Below the layer, the lateral change of the structure of the lower crust varies most greatly and ductile deformation occurs. The lower crust velocity of southern Tibet shows the reversed feature; whereas the lower crust velocity of northern Tibet increases and displays strong gradient variation and the character of the double Moho. On the whole, the Moho of the plateau is greatly undulatory. Although the crust of the Qinghai‐Tibet Plateau has a great thickness, the lithosphere does not thicken markedly. The plateau is in a state of bi‐directional compression. The unstable change of the Moho, the interaction between the crust and mantle and between the lithosphere and asthenosphere caused by the sinking of the lithospheric mantle and the strike slip and extension of the crust are the major dynamic factors for maintaining the present height and scope of the Qinghai‐Tibet Plateau.