鄂尔多斯盆地西缘构造带北段深部电性结构

在横跨鄂尔多斯盆地西缘构造带北段的查甘池—银川—五湖洞约200 km长的东西向剖面上，进行了67个测点的大地电磁探测.使用“远参考道”和Robust技术处理数据.分析了各测点视电阻率、阻抗相位、二维偏离度、电性主轴方位角、磁实感应矢量等参数，采用NLCG二维反演方法对TE和TM两种模式的数据进行了二维反演.得到的二维电性结构表明，沿剖面查汗断裂带、贺兰山东缘断裂带和黄河断裂带是明显较大型电性边界，为超壳断裂带，而三关口断裂带深部延深不大.沿剖面阿拉善地块、贺兰山褶皱带、银川断陷盆地和鄂尔多斯地块具有明显不同的深部电性结构特征.阿拉善地块内部除浅表电阻率较低外，以下到深度约50 km都表现为高电阻特性.贺兰山褶皱带电性结构复杂，电阻率高低相间.银川盆地具有上宽下窄最深达约8 km低阻层，具有断陷盆地特征.鄂尔多斯地块具有低-高-低的深部电性结构特征，成层性较明显.

Deep electric structure beneath the northern section of the western margin of the Ordos basin

We have conducted magnetotelluric (MT) sounding on a 200km-long profile across the northern section of the western margin of the Ordos basin. This profile runs in east-west direction along Chaganchi-Yinchuan-Wuhudong and has 67 measurement stations. We have used the remote reference track and Robust methods to process the acquired MT data and obtained a series of parameters at each station, including apparent resistivity, impedance phase, 2D skewness, azimuths of primary electric axes, and real magnetic induction vectors. We have also made 2D inversion with the data of TE and TM modes using the NLCG technique to determine 2D electric structure beneath the study area. The result shows that the Chahan fault, the east-edge fault of the Helanshan Mountains, and the Yellow River fault on the profile are major boundaries of electricity, which extend downward through the entire crust, while the Sanguankou fault has a small extension downward in the crust. Along the profile, the Alax block, Helanshan fold zone, Yinchuan basin and Ordos block exhibit different characters of deep electric structure, respectively. The Alashan block is largely of high resistivity down to depth 50km except the shallow subsurface of low resistivity. The Helanshan fold zone is featured by alternating high and low resistivity values. In the Yinchuan basin, there exists a low-resistivity body with a broad upper portion and a narrow lower portion at depth 8km, exhibiting a character of fault-bounded depression basin. And the deep electric structure of the Ordos block is characterized by a low-high-low resistivity pattern with conspicuous layering in the crust.