西藏高原中南部地壳与上地幔导电性结构  

Research of Conductive Structure of Crust and Upper Mantle beneath the South-Central Tibetan Plateau

作　　者：叶高峰[1] 金胜[1] 魏文博[1] Martyn Unsworth 

机构地区：[1]中国地质大学地下信息探测技术与仪器教育部重点实验室 [2]Department of Physics,University of Alberta,Edmonton,Alberta,T6G3PS,Canada

出　　处：《地球科学（中国地质大学学报）》2007年第4期491-498,共8页Earth Science-Journal of China University of Geosciences

基　　金：国土资源部"十五"青藏专项研究计划项目(No2001010202);教育部重大项目(No0211)

摘　　要：根据2001年国土资源部“十五”青藏专项研究计划项目“西藏高原南部岩石圈电性结构的大地电磁研究”所完成的吉隆一措勤剖面（800线）以及2004年教育部重大项目“藏南雅鲁藏布江缝合带地区地壳三维电性结构及其构造地质学与动力学意义的研究”所完成的定日-措迈剖面（900线）超宽频带大地电磁测深数据，研究西藏高原中南部地壳及上地幔电性结构特征及雅鲁藏布江缝合带导电性结构特征：800线和900线上地壳范围内主要为高阻区，电阻率在200～3000Ω·m之间，顶面大范围出露，底面一般在15～20km深度处，整体上，高阻区底面由南向北逐渐加深，再向北又逐渐变浅，900线高阻体底界深达30km，而800线高阻体底界更深达38km地下15～45km深度范围内存在一组电性梯度带，该电性梯度带之下存在一组硕大的高导层，其电阻率小于5Ω·m，高导层由规模不等且不连续的高导体构成．雅鲁藏布江以南的中地壳高导体，规模较小，厚度在10km左右，产状略向北倾；雅鲁藏布江以北的高导体，规模较大，厚度在30km左右，产状向北缓倾；相比之下，900线的高导体厚度较小，顶面深度较浅．通过对岩石电阻率影响因素的讨论，推测高导体的成因是部分熔融或含水流体，判断藏南巨厚的中、下地壳的物质状态是热的、软弱的、塑性的．With super-wide band magnetotelluric sounding data of Jilong-Cuoqin profile （named line 800） finished at 2001 and funded by the Ministry of Land and Resources, and Dingri-Cuornai profile （named line 900） finished at 2004 and funded by Ministry of Education, we obtained the strike direction of each MT station through strike analysis, then traced profiles perpendicular to the main strike direction, and finally got the resistivity model of each profile by Nonlinear Conjugate Gradients （NLCG） Inversion. With these two models, we have described resistivity structure features of the crust and upper mantle of the center-southern Tibetan plateau and their relationship with Yaluzangbo Suture. the upper crust of the research area is a resistive layer whose resistivity value ranges from 200 to 3 000 Ω· m; the depth of its bottom surface is about 15-20 krn in general, but the bottom surface of the resistive layer is deeper in the middle of these two profiles; at line 900 it is about 30 km deep and even at line 800 it is about 38 km deep. There is a gradient belt of resistivity at the depth of 15-45 km, with a conductive layer beneath it whose resistivity is even less than 5Ω·m. This conductive layer is composed of individual conductive bodies. At the south of Yaluzangbo suture the conductive bodies are smaller, with the thickness of about 10 km, leaning slightly to the north, but at the north of Yaluzangbo suture the conductive bodies are bigger, with the thickness of about 30 km, leaning slightly to the north too. Relatively speaking, the conductive bodies of line 900 are thinner than those of line 800, and the bottom surface of line 900 is also at a shallower depth. At last, after analyzing the factors affecting the resistivity of rocks, we concluded that the formation of the high-conductive layer was attributed to the partial melt of rocks or hydrous fluid in them. It suggests that middle and lower crust of the center-southern Tibetan plateau is very thick and hot, flabby and waxy.

关 键 词：西藏中南部 大地电磁测深 非线性共轭梯度反演 导电性结构 局部熔融. 

分 类 号：P631.3[天文地球—地质矿产勘探]