Discussion On Deep Electrical Structure Of Ordos Block And Its Neighbouring Areas

This paper is based on the national program of "SinoProbe-01-02",aiming to process the 2-D inversion of "NLCG" with the data of 10 MT profiles in the areas of ordos.The basic understanding of the areas of ordos can be concluded,after the studies of the 10 MT inversion models.Ordos block is a relatively stable block,with a stratified electronic structure.The surface is covered with low electrical resistance sedimentary cap rocks,and the crustal of the areas is with a high electrical resistance.The upper mantle is mainly characterized by low electrical resistance substances.The Moho depth of the area is about 45 km below the surface.There is a electrical boundary in the upper mantle of the areas of ordos,and its location is around N38° The electrical resistance in the north of the electrical boundary is much lower than the one in the south of the boundary.There are kinds of faults in the areas of ordos including some hidden faults,which show electrical gradient belts or disconnection of the electrical layers in the 2-D inversion profiles.In the lower crust and the upper mantle of this area,the belts of low electrical resistance or abnormity body of low electrical resistance exist,and the cause of these low electrical resistance substances may because of the salt fluids.The "solid," crust in the ordos comes into the“cap”,which can prevent the loss of the salt fluids.In the crust-mantle transition zone,the up welling of the mantle makes the substances around these areas become partially melting,which may also come into the reason of the existence of low electrical resistance substances.The wide existence of the belts of low electrical resistance and the relatively“soft”low electrical resistance substances of the upper mantle in the ordos block may provide the rotation and uplift of ordos block with a possibility.Especially in the northern area of the ordos block,thermal mantle material upwelling generates an up forth to the crust and a compressional force to fracture plane of the faults,which alters the shape of the lower crust and has a significant dynamic meaning to the study of the ordos block.