青藏高原地壳上地幔形成与演化的地球物理研究

近年来,我国在青藏高原取得了大量地球物理资料,1980-1982年中法合作又在西藏得到丰富的深部地球物理资料.青藏高原是一个整体.它的构造活动可以分为南、北、中三个带.中部是整体隆升,且已达到均衡.南北两缘受到强烈挤压、叠覆,是差异隆升,但未达到均衡.它的构造作用形式,可以分为上、中、下三层.上层(上地壳)以叠覆为主,中层(下地壳)以挤压为主,下层(异常地幔)以隆升为主.在上下地壳之间有一壳内低速低阻层,是一个主要的滑曳面.它的地质历史发展可以分为两个阶段.印度板块与西藏板块未碰撞前,异常地幔使高原缓慢隆升.在碰撞后,地壳加厚,重力均衡使高原快速隆升.

GEOPHYSICAL STUDY ON THE FORMATION AND EVOLUTION OF THE CRUST AND UPPER MANTLE OF THE QINGHAI-TIBET PLATEAU

plenty of geophysical data have been recently obtained in Qinghai-Tibet region, including the results of Sino-French joint study conducted in 1980-1982. The Qinghai-Tibet plateau is a unified geological element and may be divided into three belts according to its structural activities:the center is a uniformly uplifted block in isostatic status, while the northern and southern margins, having been subjected to intense compression and overlapping, are differential uplifts not yet reaching an isostasy. Its structural forms consist of three stru ctural layers with the upper (upper crust) dominated mainly by overlapping, the middle (lower crust) by compression, and the lower (anomalous mantle) by uplifting. An intracrustal layer of low-velocity and low-resistivity exists between the upper and lower crust, being a major sliding plane. The geological evolution of this plateau might have experienced two stages: before the collision between Indian and Tibetan plates, buoyancy of the anomalous mantle caused the pla teau to uplift gently;after the collision, the crust thickened and the plateau uplifted rapidly owing to the isostasy.