Electrical Conductivity Structure Of Crust And Mantle And Tectonic Geology Meaning In The Middle Section Of The Qinling Orogenic Belt

The hot issues about the middle section of the Qinling Orogenic Belt include:analysis of the resistivity structure of crust and mantle and evaluation of structural features;structural division of the middle section of the Qinling Orogenic Belt;the influence of intracontinental subduction of North China and Yangtze on deformation of the orogenic belt.For this reason,the paper selects the middle section of the Qinling Mountains as a research area and aims to provide an electrical reference for the solution of these problems.In the study area,nine magnetotelluric sounding profiles including 234 measurement points were placed along the longitude.From the results of phase tensor analysis,it can be seen that the two-dimensional deviation degree is small in the shallow strata of the western study area,so the stratum is mainly based on one-dimensional structures.When the frequency of the MT signal is less than 0.1 Hz,there are different degrees of polarization in different depths of the study area.Especially in the Qinling orogenic belt,there is a large degree of two-dimensional deviation,indicating that there are serious structural deformations in the deep region.From the results of GB decomposition,in the interval from Line108 to Line110,The main electrical direction of the shallow formation coincides with the fracture directions of the surface and the upper crust and it is about 120°;the structural direction of the middle-lower crust is more complex;the main direction of the lower crust and upper mantle is approximately 140°.In the local area,the low and medium frequency bands do not show obvious main directions,which may reflect the serious conductive non-uniformity in the lower crust and upper mantle lithosphere in this area.Based on the determination of the subterranean media's dimensionality and tectonic strikes,an inversion analysis of the study area was performed using the NLCG method.The two-dimensional electrical structural model of nine sections and the regional three-dimensional electrical structural model were obtained.Through the analysis of the inversion model,combined with geological and other geophysical data in the region,a reliable electrical structural model was selected.From that,the contact relationship between the major structural units in the study area and the intraplate subduction on the Qinling Mountains were discussed.From that,we can get the following preliminary results : the North Qinling is a high-resistance distribution area with a thickness of up to 50 km and the South Qinling is characterized by large-scale low resistance;the Yangtze plate with steep angle and a long distance and the North China Plate with low angle and a short distance subduct to the Qinling Orogenic Belt.