青海银石山地区巴颜喀拉前陆盆地构造变形特征及动力学机制

银石山地区巴颜喀拉前陆盆地自北而南可分为冬银山倒转褶皱带、丛崭山张公山大型向斜、屏岭银石山断褶带等3个变形特征迥异的构造单元。三叠纪末,巴颜喀拉板块北缘向北消减过程中具"双层汇聚"机制——硬度较大的基底板块仍沿其二叠纪末与昆仑地块间的俯冲分界面向北消减,相对较软的巴颜喀拉三叠系盖层则沿其底面薄弱面剥离,被动向昆仑地块之上仰冲,从而在单剪应力状态下在其北面形成北倒南倾的等斜褶皱(东部)或轴面南倾的斜歪褶皱(西部)。受昆仑地块南缘"东凸西凹"的古构造格局控制,巴颜喀拉板块在向北消减时东部具右旋走滑,使北东面巴颜喀拉山群褶皱枢纽呈北东东向,并导致北部及中部的构造变形具东强西弱的特点。盖层与基底间界面、巴颜喀拉山群三段与四段间界面等为两个主要滑脱剥离面。受其控制,在中部丛崭山张公山一带形成大型向斜,而在南部屏岭银石山地区则形成中小规模连续褶皱。

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.