Electrical Structure Of The Ordos Block And Its Relationship With The Geologial Structure

The thesis based on the No.35-40 magnetotelluric profiles data which is collected in Ordos region. In the Lab, we systemic used the advanced data processing methods, and completed the work of MT data processing to obtain a reliable MT response. After used the advanced two-dimensional inversion algorithm, we finally got the high confidence two-dimensional electrical structural model of the studies region.As the decomposition of the magnetotelluric impedance tensor show the underground electrical structure of research area is approximately a two-dimensional structure,in which electrical axis is nearly east-west direction,thus indicating the main structure of Ordos region is north-south direction.With MT sounding response analyzed.The research results show that there are distributed number of anomalous zone and electrical distortion zone, the position of the electric gradient and distortion zones roughly coincides with the major fault line delineated by regional geological data. These fault zones simultaneously are also to be the each tectonic element's dividing line fault zone in the study area. The internal electrical structure of the lithosphere in Ordos block can be divided into three layers, contain the upper and lower layer of high resistance, and the middle layer of high conductivity, the surface layer conductive bed possibly is the Cainozoic Era or Cainozoic Era's deposit formation. Study area generally development the high-conductivity layer below 30 Oumu Mi in lower crust. The high-conductivity layer development extensively and continuously within Erods block,which the main feature is:the depth in East and West are small,by contrast the middle of the profile are large.The thickness and scale of the high conductivity layer in north of the Erods block larger than the south of the Erdos block.The circle of high conductivity body development in the middle and south Erdos block,which center is a high resistivity.The east of alashan block,qilian block and the north and south lvliang upheaval in west of north china development few high conductivity body in lower crust which scale is not large. Transition zone in the western margin of Ordos widespread development of high conductive body with relatively high resistivity values and a large scale in lower crust,which occurrence is level.The depth of Moho surface is nrarly 40-45 Km in Erdos block,and the thickness of the lithosphere is 120-150Km.The Saline fluid and Partial melting interaction with the saline fluid are the reason for the high conductive layer development at the internal Erdos block, which are impossible irrelated with the buried fault in the Erdos block.The most possible reasons for high conductivity larer which developmente in lower crust and upper mantle in the fault belt located in both sides of the Erdos block are partial melting and fluid interaction.The heat source of the rock particl and the water move out of the rock is the block movement,which made fiction product heat and cause fragmentation of rock,which forming a series of fault.Material in upper mantle upwelling forming crust-mantle mixture.The crustle base in north Erdos block is khondalite,which is aluminum-rich schist with graphite gneiss folder,marble and quartzite combination of regional metamorphic rocks.So the high conductivity body in the internal north of the Erdos block maybe due to the Graphite.the low resistivity body in the western margin of Ordos fold belt which the material in Tibetan Plateau escaped development continuously,which scale is large.