Deep features of continental collision belts in northwestern China and their dynamic implications

Possible colliding types between orogenic belts and adjacent blocks are rec ognized in northwestern Chinese continent by analyzing the deep frames of t he lithosphere and asthenosphere of continental blocks,based on the results of seismic tomography. Several tectonic patterns, such as the embedding, s ubducting, detaching and lateral inserting of continental lithosphere,are o bserved between the Tianshan and Tarim regions. Sharp deep bound aries exis t between the Qinghai-Xizang Plateau and its northern geological provinces, showing the evidences of upper mantle flowing to north. It is inferred that the lithosphere of the Qinghai-Xizang Plateau has been flexed or broken in the northward moving process,resisted by the rigid Tarim block. Neverthele ss, the shallower asthenosphere north of the Qilian mountain seems to be a free boundary,which makes the upper mantle substances beneath the plateau t ransporting northward much further. Continental collision not only changed the lithospheric structure of the orogenic belts in western China, but also resulted in the mantle upwelling from asthenosphere to the base of lithsop here along the colliding boundary. They have played a key role in the evolu tion of the plateau and other orogenic belts in western China.