青藏高原构造动力及变形机制的弹性有限元分析

THE ANALYSIS OF TECTONIC DYNAMICS AND DEFORMATION MECHANICS OF QINGHAI-XIZANG PLATEAU BY ELASTIC FINITE ELEMENT METHOD

利用现今青藏高原地质和地球物理研究成果,本文建立了垂直高原总体构造走向的南北向直立剖面的有限元模型,其根据实际资料,划分成分层和有限单元。在此模型基础上进行弹性材料的计算模拟和分析。 印度板块向北运动挤压、高原北部岩石圈阻碍及软流圈拖曳是青藏高原北移变形、隆升和地壳增厚的动力机制;重力及其均衡调整作用是地体间相对运动和地体内差异运动的主要动力,另外青藏高原还受地壳和上地幔结构构造的影响。计算模拟还得到了一些有实际意义的结果,如活动的地质构造和地球物理现象的分带集中、主边界和雅鲁藏布江等地体边界断裂的逆冲性质、各地体南部地表的南倾正断层及喜马拉雅山南坡向南的重力推覆等。

Based on the multi-descipline studies in Himalayan region, especially on the recent achievements of the Global Geoscience Transect (GGT) from Yadong to Golmud, an elastic finite element model is set up to model and analyze the tectonic movements and dynamics in Qinghai-Xizang plateau.The dynamical environment of the plateau tectonics is determined as follows:1) The crust and upper mantle have been pushed at. the south boundary by the Indian plate and are moving northward now; 2) This movement is slowed by sticky flow in the asthenosphere under the plateau and the resistance of the relatively stable north of the plateau and the terranes farther north, the movement decreasing gradually northward at the boundary surface between the upper mantle and the asthenosphere under the plateau; 3) The gravity and isostasy of the geological bodies in the plateau also play an important role in the tectonics.Some geophysical phenomena and structural processes are reflected in the modelling. The uplifting and thickening of the plateau crust are chiefly the results of the northward movement and compression of Indian Plate and the apparent effects of these deformations reach the Nujiang river region now. The isostatic anomalies in the active region near the Main Boundary Thrust (MBT) are concordant with the bending deformation of the crust caused by the horizontal compression, viz. the negative anomalies with the subsidence to the south and the positive anomalies with the uplift to the north. The crust and the upper mantle structures of the plateau, anted by gravity and isostasy, control the relative movements of terranes and stru- ctural deformation in these terranes, e. g., the thrust characteristics of the MBT and Yalung Zangbo Suture Zone (YZSZ), the normal faults in upper crust of the southern parts of Himalayan, Gangdise-Nyainqentanglha and southern part of Qiangtang terranes with their fault planes dipping to north, and the gravitational overthrusts at the south hillside of Himalaya. The high heat flow in the area around YZSZ is probably caused by the convergent movement trend of the hot upper mantle materials.The above computation results are all in fairly good accordance with the observations and measurements in the field works.