Study Of Lithospheric Conductivity Structure Of Western Ordos Block

This paper is based on the deep detection technology and experimental research projects"SinoProbe-01-02".The study area lies in the range E104°-E107°,N35°-N400°,its south west is the Qilian block,it abuts the Alashan block in the north west,and the Ordos block lies in the east.Through the skewness analysis and impedance tensor decomposition of the data,the paper identified the deep electric structure of study area is approximately a two-dimensional structure,the main structure of the south block is nearly north-west or north-north-west,and nearly north-east or the north-north-east in the north block.According to that,we choose 4 lines to survey the study area and construct the model based on the tectonic of research area.Through the application of 2-d inversion algorithm of "NLCG" of the 4 lines,we finally got a model of lithospheric electrical structure in the study region.The results show that in the study region,along the line direction the location of electric gradient and distortion zone,roughly coincides with the major fault line delineated by regional geological data.Maxianshan,Haiyuan-liupan,Qingtongxia-Guyuan and Yellow River faults are correspond to the contact zones between blocks or between a block and a boundary zone.The electrical structure of crust-mantle beneath the Qilian,Alashan and Ordos blocks exist low electrical resistance or abnormity body.Below the study region,deep electric structures are complicated,where high-resistivity(HR)and low-resistivity(LR)bodies are mixed,thus the large scale layered LR material are destroyed.In the Haiyuan boundary zone,the shallow crust is wide in north and narrow in south,spreading out toward northwest and converging to southeast.In the Yingchuan boundary zone,HR and LR bodies are mixed.The structure of the study area shows,stable or weakly deformed blocks have layered structure,and highly active and deformed blocks in the tectonic boundary zones have complex electric structure.