Structural deformation and dynamic mechanisms of the Bayan Har (foreland) basin in the Yinshishan region, Qinghai

The Bayan Har foreland basin in the Yinshishan region, Qinghai may be divided, from the north to the south, into three tectonic units, i.e. Dongyinshan overturned fold zone, Congzhanshan-Zhanggongshan (syncline), and Pingling-Yinshishan fault-fold zone. A "double-layer collision" mechanism once operated when the northern margin of the Bayan Har plate subducted northwards during the latest Triassic. The harder basement subducted northwards beneath the Kunlun block, while the softer Bayan Har Triassic cover was splitted off and passively obducted onto the Kunlun block, resulting in the formation of the isoclinal (east) or inclined (west) folds in the north created by simple shear stress. Constrained by the "east-convex and west-concave" palaeotectonic framework of the southern margin of the Kunlun block, the Bayan Har plate displays dextral strike slipping, and caused the axial lines of the Bayan Har Mountains Group folds to be oriented NEE when the plate was moving northwards. The tectonic deformation in the northern and central parts appeared to be intense in the east and weak in the west. There exist two strike-slip planes, i.e. the cover-basement boundary and the boundary between the third and fourth members of the Bayan Har Group, which resulted in the formation of the large-scale syncline in the Congzhanshan-Zhanggongshan zone in the central part and of small-scale continuous folds in the Pingling-Yinshishan zone in the southern part.