喜马拉雅“东构造结”地区的特异重力场与深部地壳结构

Specific gravity field and deep crustal structure of the 'Himalayas east structural knot'

跨越中、印、缅三国交界的喜马拉雅“东构造结”地区(92°E^97°E,26°N^30°N)有一半以上的面积尚没有重力测点,是重力数据空白区,故无法直接研究其重力场特征与深部地壳结构(构造).本文应用卫星重力异常资料作为近似空间重力异常,经计算给出的布格重力异常,其特征与该地区的地形高程呈很好的镜像相关.据此得到该区不同方位的3个地壳深部结构剖面.重力异常反演求得青藏高原地壳厚度>70 km;喜马拉雅造山带为55 km左右;布拉马普特拉河谷盆地为33~35 km;那加山山脉地区为40~45 km,即呈现出3个不同构造单元的展布.同时求得“东构造结”区由高密度的刚性物质构成,在印度洋板块的碰撞、挤压作用下呈向北运移,并插入青藏高原东缘.基于这样的构造格局和深层动力过程,导致了青藏高原东南缘和东北缘的强烈构造运动,大、小地震的频频发生和矿产资源的聚集.

More than a half of the ＇ Himalayas east structural knot＇ area （92°E - 97°E, 26°N - 30°N） that straddles boundaries between China, India and Burma has no ground gravity measuring point yet. Here it is hard to research directly the gravity field characteristic and the deep crustal structure. In this paper, the satellite gravity anomaly data are employed as pseudo free air gravity anomaly to calculate Bouguer gravity anomaly. The calculated Bouguer gravity anomaly exhibits well mirror correlation with the topography altitude of this district. Three profiles of deep crustal structure according to above calculation are obtained. In the Qinghai-Xizang Plateau the crust thickness is more than 70 km, in the orogenic belt of Himalayan Mountains it is about 55 km, in the Brahmaputra basin valley it is 33 to 35 km, and in the Naga mountain it is 40 to 45 kin. The ＇east structural knot＇ is composed of high-density matter, moves northward after the collision and extrusion by the Indian Ocean plate, and then inserts into the eastern margin of the Qinghai-Xizang Plateau. This dynamic process results in violent tectonic movement of the southeastern and northeastern edges of the Qinghai-Xizang Plateau, induces a series of earthquakes frequently, and accumulates a large amount of mineral resources.