南北地震带南段川滇黔接壤区电性结构特征和孕震环境  

Electrical structure and seismogenic environment along the border region of Yunnan,Sichuan and Guizhou in the south of the North-South seismic belt

作　　者：程远志[1] 汤吉[1] 陈小斌[1] 董泽义[1] 肖骑彬[1] 汪利波 

机构地区：[1]中国地震局地质研究所地震动力学国家重点实验室,北京100029 [2]江西省地震局,南昌330039

出　　处：《地球物理学报》2015年第11期3965-3981,共17页Chinese Journal of Geophysics

基　　金：地震行业科研专项项目(201008001-02)资助

摘　　要：本文利用大地电磁测深数据,对穿过兰坪—思茅地块和川滇菱形地块以及进入扬子地块的云南兰坪—贵州贵阳大地电磁测深剖面展开了深部电性结构研究.采用大地电磁数据处理分析以及反演技术,对观测资料进行了由定性到定量全面地分析,通过二维非线性共轭梯度反演得到了沿剖面的较为详细的地壳上地幔电性结构,结合其他地质和地球物理资料的分析,对该剖面的二维电性结构进行解释,确定了主要断裂带和边界带的位置以及深部延伸情况,同时确定了壳内低阻层的分布位置,最后进行了区域动力学和孕震构造环境的探讨.研究表明:剖面壳幔电性结构分块性特征与区域地质构造分布特征基本一致,不同地块的电性结构存在显著差异,其中川滇菱形地块的结构相对复杂,上地壳的电性结构为高低阻相间分布特征,电阻率的突变带与地表断裂具有很好的对应关系;兰坪—思茅地块存在中上地壳低阻层,川滇菱形地块中西部存在下地壳低阻层,川滇菱形地块东部和华南地块西部存在中上地壳的低阻层;川滇菱形地块中部攀枝花附近的低阻层埋深最深,而华南地块西部会泽附近的低阻层埋深则最浅;兰坪—思茅地块和川滇菱形地块的中下地壳的低阻层可能与青藏高原物质的东南逃逸有关;华南块体的宣威以东的下地壳不存在低阻层,华南块体下地壳和上地幔的电阻率较高;攀枝花附近的高阻体可能是峨眉山玄武岩喷发导致底侵作用及幔源物质上侵的结果.The Tibetan plateau is the result of the collision of the Indian and Eurasian plates during the Cenozoic,which began circa 50 Ma.The southeastern margin of the Tibetan plateau is located between the plateau and the South China block,including most of Sichuan and Yunnan provinces and a part of Guizhou in southwest China.They have been extensively studied.Several models have been proposed to explain the deformation and uplift of the eastern Tibetan plateau.The first model is that lateral extrusion of rigid blocks created the major strike-slip faults in the region,and in the second model,ductile channel flow in the middle/lower crust causes the thickening of the crust and uplift of the plateau.The debates of these models center on whether the deformation is localized in the mantle or in the upper crust.In order to study the deep electrical structure of the southeastern margin of the Tibetan plateau,MT data along the profile L2 were collected during the period from June to September in2011.The observation equipment was MTU-5Asystems manufactured by Phoenix of Canada and LEMI-417 made in Ukraine.All five components of the time-varying electromagnetic field（Ex,Ey,Hx,Hyand Hz）were recorded at every MT site.The total length of the MT profile was about 750 km.The number of super-long period MT sites,long period MT sites and conventional MT sites was 12,52 and 58,respectively.The average site span was approximately 7km.Time series were continuously recorded at each site for about 20 hours in the case of conventional MT,40 hours for long-period MT and 10~15 days for super-long-period MT experiment.The sounding frequencies of the super-long period MT site,long-period MT site and conventional MT site are 320Hz^30000s,320Hz^5000sand 320Hz^2000s,respectively,which were suitable to invert the structure of the crust-uppermost mantle in the area.The remote reference MT technique and the robust data processing method were employed.The subsurface dimensionality and directionality were assessed using the Bahr tensor decomposition

关 键 词：南北地震带 大地电磁测深 电性结构 低阻层 地震构造 

分 类 号：P315[天文地球—地震学] P631[天文地球—固体地球物理学]