摘要
笔者等完成的亚东—格尔木和格尔木—额济纳旗地学大断面揭示出青藏高原岩石圈的基本结构、组成、演化和地球动力学过程,发现了印度板块在南缘向喜马拉雅山下俯冲、阿拉善地块在北缘向高原下楔入的证据,它们构成了使高原隆升的主要驱动力。多学科研究表明,青藏高原是一个由8个地体拼合的大陆。高原内部地壳20～30km深度附近普遍发育低速高导层,它是构造应力去偶层,其上地壳脆性变形,逆冲叠覆,缩短增厚;其下地壳结构横向变化大,韧性变形。藏南下地壳(50～70km)速度发生逆转;而藏北下地壳速度增高并呈梯度变化,具有双莫霍面特征。高原莫霍面起伏变化大,南北边缘山脉山根特征明显,在高原内部缝合带两侧莫霍面多有断错。虽然高原地壳巨厚,但是岩石圈地幔并没有增厚。高原隆升经历了俯冲碰撞(K_2—E_2)、会聚挤压(E_3—N_1)、及均衡凋整(N_2—Q)3个阶段。青藏高原岩石圈现今处于双向挤压的动力学环境,莫霍面的不稳定变化,岩石圈地幔下沉等因素引起的壳幔之间和岩石圈与软流圈之间的相互作用,地壳的走滑与拉伸作用,是维持高原现今高度和范围的主要动力学因素。
During 1986 ~ 1995. the authors separately compiled the Yadong-Golmud geoscience transect (1986~1990) and the Golmud--Ejin geoscience transect (1991~1995) supported by the Ministry of Geology and Mineral Resources of P. R. China and the National Natural Science Foundation of China. The two transects link up to form the Yadong- Golmud-Ejin geoscience transect passing through the whole Qinghai-Tibet Plateau, from south to north, totalling about 2400 km long, which is called the TGT (Tibet Geoscience Transect) for short. TGT revealed the basic structures, tectonic evolution and geodynamic process of the lithosphere of the Qinghai-Tibet plateau. The evidence of underthrusting of the Indian plate beneath the Himalayan Mountains on the southern margin and southward wedging of the Alaxa block on the northern margin beneath the plateau has been found. They were the driving forces causing the plateau uplift. The plateau is a continent resulting from amalgamation of eight terranes. These terranes are separated by sutures or large-scale faults, different terranes have different lateral inhomogeneity and multi-layered lithospheric structures. At depths of about 20~30 km of the crust in the interior of the plateau there commonly exist low-velocity layers. It is an uncoupled layer of the tectonic stress; above the layer, the upper crustal slices were thrust and overlapped each other and the rocks underwent brittle deformation, thus leading to shortening and thickening of the upper crust. Below the layer, the lateral change of the structure of the lower crust varies most greatly and ductile deformation is found. The lower crust velocity of the Himalaya terrane shows the reversed features; the lower crust velocity of the Gangdise terrane shows strong gradient variation and shows the character of the double Moho. On the whole the Moho of the plateau is greatly undulatory, on the north and south sides the characteristics of the mountain root are very conspicuous; and the Moho is displaced in many places across the suture zone or gigantic faults. Although the crust of the Qinghai-Tibet Plateau has a great thickness, the lithosphere does not thicken markedly. The plateau uplift evolved through three stages; uplift due to subduction and collision (K2-E2); uplift due to convergence and compression (E3-N1) and uplift due to isostatic adjustment (N2-Q). The plateau is in a state of bi-directional compression. The unstabel change of the Moho, the interaction between the crust and mantle and between the lithosphere and asthenosphere caused by the sinking of the lithospheric mantle and the strike-slip and extension of the crust are the major dynamic factors for maintaining the present height and scope of the Qinghai-Tibet plateau.
出处
《地质论评》
CAS
CSCD
北大核心
1998年第4期389-395,共7页
Geological Review
基金
中国地质矿产部和国家自然科学基金会联合重点资助项目
关键词
青藏高原
岩石圈
地学断面
地球动力学
Qinghai-Tibet Plateau
lithosphere
geoscience transect
continental dynamics
