青藏高原东边缘冕宁—宜宾剖面电性结构及其构造意义  

The electrical structure of the crust along Mianning-Yibin profile in the eastern edge of Tibetan plateau and its tectonic implications

作　　者：万战生[1,2] 赵国泽[1] 汤吉[1] 陈小斌[1] 王立凤[1] 肖骑彬[1] 詹艳[1] 王继军[1] 汪卫毛[3] 蔡军涛[1,4] 

机构地区：[1]中国地震局地质研究所,北京100029 [2]河北省地球物理勘查院,廊坊065000 [3]中石化江汉石油管理局地球物理勘探公司,湖北潜江433124 [4]江苏省地震局,南京210014

出　　处：《地球物理学报》2010年第3期585-594,共10页Chinese Journal of Geophysics

基　　金：国家重点基础研究发展计划项目(2004CB418402);国家自然科学基金重点项目(40534023)资助

摘　　要：在青藏高原东边缘沿冕宁宜宾进行了大地电磁探测研究,剖面西起康滇地轴,向东穿过大凉山地块,终止于四川盆地.利用带地形的NLCG(非线性共轭梯度)方法对资料进行了反演,得到沿剖面的二维电性结构.康滇地轴和大凉山地块地壳中存在向上拱起的高导层(HCL),顶面埋深为10～1 5 km,最浅处不足10 km,厚度大约15～25 km,最小电阻率小于10 Ωm.四川盆地中下地壳不存在高导层.和该剖面北侧的石棉乐山剖面的地壳电性结构对比分析表明,高导层在南北方向上可能连续延伸,长度大于100km.壳内高导层的高导电性与岩石的部分熔融有关,并可能含有百分之几的含盐流体,易于流动和变形.青藏高原东部地壳内的可流动层在向东或东南方向流动过程中,由于受到四川盆地的阻挡,转向南或南南东方向,大体沿着大凉山地块的走向.在东西方向,壳内高导层自川滇地块向东运动,穿过大凉山地块西边界的安宁河断裂和则木河断裂,在大凉山地块东部,向四川盆地深部倾俯.本文对于壳内可流动层的存在及其与青藏高原东边缘的变形和地震活动性的关系进行了探讨.A magnetotelluric sounding was carried out in the eastern edge of Tibetan plateau along Mianning-Yibin that starts from Kangdian Geo-axis （KDG） eastward crossing the Daliangshan block （DLSb） and ends in Sichuan basin block （SCb）. A 2-D modeling with consideration of topography is used with the NLCG （Nonlinear conjugate gradient method） inversion. 2-D electrical structure model of crust and upper mantle was constructed. The upward arched high conductive layer （HCL） exists in the crust of both KDG and DLSb, but not in SCb. The HCL has a low resistivity of 3-10 Ωm and its top is about 10--15 km deep （the shallowest less than 10km） with a thickness about 15-25 km. The crustal electrical structure combined with that of Shimian-Leshan profile indicates that the HCL is continuous and extends for more than 100 km in south-north direction. The high conductivity of HCL may be related to partial melt of rocks and some quantity of salt fluid prone to deformation and flow. The flow of HCL under the pushing force from Tibetan plateau is directed to E and/or SE in eastern Tibet plateau, and then turns to S or SSE in DLSb due to the obstruction of Sichuan basin. In EW direction it crosses the west boundary of DLSb, Anninghe fault （ANHf） and Zemuhe fault （ZMHf）. The crust flow layer in the eastern DLSb underthrusts eastward beneath SCb. The relationship between the flow of HCL and the tectonic deformation of the crust and the seismicity is analysed in the article.

关 键 词：青藏高原东边缘 大凉山地块 电性结构 地壳流动层 地震活动性 

分 类 号：P541[天文地球—构造地质学] P631[天文地球—地质学]