华北中部岩石圈电性结构——应县—商河剖面大地电磁测深研究

Conductivity Structure of Lithosphere in Central North China: Magnetotelluric Study of Yingxian-Shanghe profile

20 0 1年 ,沿着山西应县到山东商河 ,重新布置大地电磁测深剖面进行研究 .采用现代先进的大地电磁数据处理技术和快速松弛二维反演方法获得该剖面二维电性结构模型 ,从而充分展示了华北地区岩石圈电性结构的特点 .从电性特征上讲 ,华北岩石圈以太行山前断裂为界划分为东、西两区 ,东区为低阻区 ,西区为高阻区 .在东区 ,上地壳电性结构基本与华北裂谷系的隆、坳构造格局相对应 ,岩石圈的电导最高达 3× 10 4 S ,远远大于强烈活动的安第斯山岩浆弧区和西藏高原岩石圈的电导 .这里 ,在构造连接部位的地壳中有不连续的高导体存在 ,电导率大约 0 .1～ 0 .8S/m .在西区 ,太行山和恒山的岩石圈为高阻块体 ,表现出稳定大陆区岩石圈导电性结构的特点 .但恒山高阻块体之下发现一组向西缓倾的高导层 ,其电导率为 0 .0 4～0 .2 5S/m ,顶面在 2 0km深处 ,底面深度大约 40km .

In 2001, an MT sounding profile was relocated from Yingxian, Shanxi Province to Shanghe, Shandong Province. The advanced MT data processing method and rapid release inversion (RRI) were employed to establish a 2D model of conductivity structure showing fully the features of conductivity structure of the lithosphere in North China. In terms of conductivity, the North China lithosphere is classified as eastern and western parts with the frontal fault in the Taihang mountain as the corresponding boundary line. The eastern part is characterized by the low resistance conductivity, and the western part is characterized by the high resistance conductivity. In the eastern part, the conductivity structure in the upper crust corresponds roughly to the uplift and depression tectonic structure of the North China rift system, with the maximum conductivity of the lithosphere reaching 3×10 4 S, far greater than that of magma arc area in Andes and the lithosphere of the Tibet plateau where the volcanic activities are violent. Here, discontinuous highly conductive bodies, whose conductivity is about 0.1-0.8 S/m, are present in the crust of the contact zone. In the western part, the lithosphere of the Taihang and Hengshan mountains, composed of high resistance conductivity bodies, is characterized by the conductivity structure of a stable continental lithosphere. However, a group of westward inclined highly conductive layers, whose conductivity is 0.04-0.25 S/m, whose top layer is located at the depth of 20 km and whose bottom layer is located at the depth of around 40 km, were discovered under the Hengshan high resistance conductivity body