Study For The 3D Electrical Structure Within Qiangtang Terrane

This dissertation is supported by "Deep Exploration Technology and Experimentation" set up the project of " Experimental Study of the Continental Standard Grid of Electromagnetic Parameters(SinoProbe-01)".In order to design a theoretical mode which match to the actual geological characteristics in Qiangtang terrane,all kinds of geological imformation about Qiangtang terrane will be collected.Comparing the different theoretical mode and invertion results to analyse the geological characteristics in the results of invertion.Then based on the magnetotelluric(MT)sounding data from eight prifiles,which distributed in the west,middle and east of the Qiangtang terrane,finished by China University of Geosicences.the dissertion applied advanced MT data processing technology and two-dimensional algorithm to data processing and invertion,in order to researches the structrue of the shell and mentle,local tectonic and deep material status in Qiangtang terrance.According to the geological imformation of the terrance,applying the 3D module of WinGLink software to design a model of "high resistance,low resistance and high resistance layer model which have a vertical fault," forward calculation obtain the same cross section of magnetotelluric surveying data with the actual standard point 11 point construction method.The results of electromagnetism data's tensor anolysis shows that the Qiangtang terrance is a 2D tectonic,the electrical axis' direction in the most of the region is EW,the electrical structure of the the qiangtang terrance appears as in the south-north direction it can be divided into zones or belts,in the east-west direction divided into blocks or segments,and vertically appears spheres or layers.The Qiangtang tarrence crust can be broadly divided into three electrical layers,of which the second layer is the high conductivity layer,the depth is 30?100km,that is,the middle and lower crustal are high conductivity layer.The distribution of the high conductivity layer deffers a lot in different plots.In Qiangtang block,the high conductivity layer can be clearly divided into two parts,which are located in the South an North Qiangtang respectively.According to the results of the electrical strcture model of the Qiangtang terrance got from 2D inversion,the electrical grad area and distortion area diribution in upper crust fits the fault zone delineated by the geology data,and it could reflect the depth feature of the fracture tectonic zone.Especially in the area near the Lungmu Co-shuanghu suture and xijir Ulan Jinsha River suture,the results of inversion shows that at the both side of the suture,the scale and thickness of the electrical structure,particularly high conductivity layer,has big difference.The crustal high conductivity layer within Qiangtang.The phenomenon is perhaps due to the effect by the plate movement.in the depth of the Qiangtang tarrance the high conductivity may caused by the heating effect of upwelling mantle-derived material,leading to the warming up and thus partial melting of middle and lower crustal rock.