青藏高原亚东-格尔木地学断面

THE YADONG-GOLMUD GEOSCIENCE SECTION ON THE QINGHAI-TIBET PLATEAU

据大量的地质资料和地球物理数据,对青藏高原划分了6个地体,虽然该区地壳是分块的,但该区仍是一个独立完整的岩石圈构造单元;若从安多分界,南北地壳结构、构造不同。南部构造复杂,北部简单。经研究本区地壳的缩短与加厚,主要与板片俯冲和逆冲、叠覆等8种因素有关。本区隆升的力学机制,可能是以印度板块向北挤压力为主,同时受到欧亚板块向南挤压力。这种双向挤压力,导致软流圈运动,同时还受到核幔边界突起热的影响。

Six terranes have been distinguished on the Qinghai-Tibet Plateau. From south to north they are the Himalaya terrane, the Gangdise terrane, the Qiangtang terrane, the Bayan Har terrane, the Southern Kunlun terrane and the Northern Kunlun terrane. These terranes were mostly positioned at the middle-low latitude areas of the southern hemisphere during the Palaeozoic, and then they dirfted and accreted to the margings of the Eurasian continent and finally were assembled to form the Qinghai-Tibet Plateau. The crust is obviously divided into blocks, but the Qinghai-Tibet Plateau is a single integrated lithospheric continent. Geophysical data indicate that with Amdo as a boundary the plateau may be divided into two parts with different crustal structures. In general, the northern part is characterized by relatively simple crustal structure, thick crust and mantle, cold crust and relative stability of the crust; while the southern part is characterized by relatively complex crustal structure, thick crust but thin mantle, warm crust and strong activity. The uplift and thickening are due to (1) slab subduction and overthrusting, (2) crust and mantle mixing, (3) thermal activity caused by doming at the core and mantle boundary, (4) magma injection, (5) creeping deformation, (6) large-scale strike-slip faulting, (7) folding, and (8) gravitational isostasy. The shortening and thickening of the plateau took place in multiple stages and in succession, isostatic adjustment was accomplished step by step, and the crustal compression is a continuous process. The focal plane dips south to the north of the Himalayan Mountains and north to the south of the Himalayas, which reflects the modern stress field state: the plateau is undergoing bilateral compressiòn, i.e. northward compression of the Indian plate and southward compression of the Eurasian plate (with the former predominating), thus leading to crustal isostasy and thermal activity. This shows that the asthenospheric movements are even affected by the doming and thermal activity at the boundary between the mantle and core.