Electrical Structure Study Of The Crust-upper Mantle In Dabie-Sulu Orogen

In the study, the existent magnetotelluric data and the latest data of long period and normal MT are used, with advanced data-processing technique, we provide rather reliable electrical structure of crust-upper mantle in Dabie-Sulu orogen. Combining with the basic geology and using the advancement of MT, we emphasize our study on the following: the suture in Dabie-Sulu orogen, the boundary of each block, the location and extending status in depth of main faults, the contact relation in depth and possible interaction of Yangtz block, orogen and North China block, the possible status of lithosphere, the situation in depth of HP-UHP metamoprhic zone together with the relation with the wall rock. So to speculate on the exhumation procedure of HP-UHP metamorphic rock in depth, the dynamic procedure of orogen's evolvement, addtionally, to provide geophysical evidence for orogen study.Firstly, some frequently encountered problems in the process of MT data-interpreting are proposed, together with a brief discussing of the theory of distortion and static shift with their mostly used settlement, the advancement and disadvantage of two-dimensional inversion methods, the disposal methods of error and polarization mode in two-dimensional inveriosn.Secondly, emphases are on Dabie orogen, after a brief introduction and analysis of the basis geology between Dabie and Qinling orogen, with the existent MT data, three profiles in Dabie orogen are designed, the profiles, across the high-ultrahigh pressure metamorphic belt, were in NE28o directions.With 2D inversion program of Non-linear conjugate gradient method, three profiles'two-dimensional electrical structures of crust-upper mantle of Dabie orogen are obtained. Based on the two-dimensional electrical structures, a 3D model is made by Kringing interpolation. Then, the model's electromagnetic responses are computed with 3D finite difference forward program, the response apparent resistivity and phase curves coincide with the observed data well. So to say, the 2D inversion results are reliable. From the electrical plane slice of different depth in Dabie orogen, the strike of electrical structure shows a transition from nearly EW to SN direction with the depth increasing. It indicates that the materials of lower-crust and upper-mantle under Dabie orogen have experienced post-orogeny rheological adjustment. The 2D electrical structures of three profiles are comparable, and can be divided into four layers in vertical direction, that is, the surface cover layer, the mid-upper crust high resistivity layer, the inner crust relatively low resistivity layer and the mantle. In horizontal direction, The North Huaiyang Tectonic Belt and Dabie Block are different tectonic units in electrical structure, they are separated by Xiaotian-Mozitan fault, which dips north and extends downto the upper mantle. In Dabie Block, the thickest place of the mid-upper crust high resistivity layer is along Luotian-Qichun- Yingsan-Yuexi. The Dabie Block is of massive structure in electricity, it does not support the division of North and South Dabie. In Dabie Block, there maybe exist channels of granitic magma activity of Jurassic and Cretaceous period, which make further uplift of the Ultra-high pressure metamorphic rocks and affect the distribution of inner-crust high conductive layer and cause great difference in depth of the high conductive layer. At the end of this chapter, the dynamic model of Dabie orogen's evolvement is discussed.