The deformation transfer from orogen stage to plateau stage in the central part of Tibetan Plateau during Miocene time and it′s tectonic mechanism

Based on a review of the previous researches,we find that the geology evolution of the Tibetan Plateau is closely related to the tectonic deformation of the southeastern margin of the plateau.The subducting India crust partially melts under south Tibet and injects into the middle plateau crust.The weak,rheological plateau middle crust materials flowed away from the plateau via two tunnels:the old one is the Indochina Tunnel,opened before 35 Ma and closed at 12 Ma, the younger is the Chuandian Tunnel,opened at 12 Ma and continues till now.Because of the intense press deformation between the Eastern Himalayan Syntax and the Sichuan Basin,the width of the Indochina Tunnel became narrow from the Eocene to the middle Miocene and closed at 12 Ma.The flowing velocity of the weak middle crust materials changed significantly during the Miocene time because of the opening and closing of the two tunnels and the differences of mechanic properties of the middle crust under the Indochina Tunnel and the Chuandian Tunnel. The velocity of flowing out is less than the velocity of injection from 23 Ma to now,and reached to the minimum at 12 Ma.The rheological middle crust materials enclosed in the plateau crust cause the high and flat plateau surface to develop and outward expand from the central plateau to both south and north.With the mechanical analysis,the evolution of the central plateau is divided into two stages,the orogen stage controlled by the orogen mechanism,from 35 Ma ago till 23 Ma,and the plateau stage controlled by the plateau mechanism,from 23 Ma till now.