Study For The 3D Electrical Structure Within Bangong-nu Jiang Suture And Its Adjacent Areas

Bangong- Nujiang suture zone across the central plateau,stretches over 3000 km in the eastwest direction. It is an important geological boundary in the central plateau. Suture zone north and south sides are Lhasa terrane and Qiangtang terrane. These two terranes occupy the middle of the Tibetan Plateau. Previous studies shows that, there are big differences between Lhasa and Qiangtang terrane in magmatic activity、lithospheric structure and geophysical field characteristics aspects, indicates that Lhasa and Qiangtang terrane may be experienced different tectonic evolution history. Depth understanding of underground structures of suture zone and its adjacent areas has great significance for understanding the evolution of the Tethys and the Tibetan Plateau shortening and uplift process. Magnetotellurics is an important method for the detection of the electrical structure of the lithosphere. The study select Bangong-Nujiang suture zone and its adjacent areas as research area, process and analyze the data of magnetotellurics wide band array data in the area, use two- dimension and three- dimension forward and inversion technique to construct three dimensional electrical structure model of crustal scale and research electrical structure of this area. The study is based on subordinate subject(“SinoProbe-01”) of “Chinese Continental Deep Detection Technology and Experimental Research”.The results of this study show that: the electrical structure model of the study area can be roughly divided into three electrical layers in the 100 km scale range—the high resistivity layer of upper crust, high conductivity layer of middle and lower crustal and Medium resistivity layer of deep crust to uppermost mantle. The change of electrical structure in the transverse direction is more complicated than that in the vertical direction. There are differences in the electrical properties of the two sides of the suture zone. There are differences in the electrical properties of different regions in the same area too. The deep area of the high resistivity layer is mainly distributed near the suture zone. The high conductivity layer in Lhasa terrane shows the distribution characteristics of “the shallow west and the deep east". The high conductivity layer in Qiangtang terrane distribute mainly over North West Direction.The high resistance characteristic of upper crust is the embodiment of the magmatic rocks which are widely developed in the shallow part of the plateau. Lower extension of high resistance body near the suture zone may be the result of cooling of magmatic activity that induced by the subduction of the Northern New Tethys Ocean. The high conductivity layer in Lhasa terrane may be related to partial melting of lower crust that induced by the subduction of India plate to Lhasa and crustal thickening of Lhasa terrane. There is a good correspondence between the high conductor in Qiangtang terrane and the Longmu Co-Shuanghu fault zone in space. Combined with the gravity anomaly data to infer the Longmu Co-Shuanghu suture zone is a large cutting depth of the suture zone. The thermal mass and the heat flux of the mantle flow along the suture zone to the crust, causing the partial melting of the crustal material, which leads to the high conductivity in the electric structure.