Study Of Electric Structure Of Guidong-Xiamen Profile In South China With MT Method

This paper studies the geotectonics, crust and mantle structure, features of faults and the distribution of granite in south China basing on the subject of Magnetotelluric Observation and Experiment in South China and focusing on the complicated geological structure and deep physical properities in south China. The paper gets an electric model of Guidong-Xiamen profile in south China, this model provides new reliance to the electric relationship of the lithoshpere and asthenoshpere with the deeper mantle.During the data processing, we removed the noise from the wild field measured data with artifical flitering method and remote reference manetotelluric method. The processed data are much more smooth, reliable and regular than before. Tensor decomposition method is carried out to acquire the geoelctric strike and skewness, tipper and real induction vector are also used combined with tensor decomposition to make the calculated strike and skewness values more accurate. The strike value of each site changes from one site to the other, most of the strikes are northeastern. There are also some sites with northwestern and east-west stirke. The whole profile is nearly two-dimension, there are only few sites with there dimensional strike. Deep study of real inductin vector of one measured frequency has shown that the real induction vector is a trustable parameter in the evaluation of geoelectric strike. Its reversion is a good evidence of the existance of faults and low-resisitvity region. The vectors play an important role in the data processing of Guidong-Xiamen profile.Focusing on the complicated geological condition and the deep exploration object, this paper mainly studies the geoelectric strike of Guidong-Xiamen profile, the electric features of the lithosphere and asthenosphere, the distribution of granite in this profile at the same time with forward and inversion methods. The paper also researches the electirc features of the around crust and mantle, lithosphere and asthenosphere, aslo with the distribution and types of the granite in this profile. According to the forward and inversion results, the paper figures out the electric structure model of the profile, including the information of faults, granite distribution, high conductive layer in upper mantle and so on. There are two regions (site 1-4, site 21-34) with high resistivity which are defined as the uplifting regions of the asthenosphere. The electric struture model and geological model are finally constructed after the numerical simulation, the two models provides a good basement to the further interpretation work.The paper mainly gets the following results through the study above:①There is a big range of high resistivity region in the inversion profile with the value of 10000 ? ?m. This is interpreted to be the granite region with mantle source and crust source, these granite consist the extensive granite belts in Guidong-Xiamen profile. There are fault belts exsiting along the granite region and they control the distribution of the granite;②The depth of the lithosphere in inland and coast region is not consitant, basically, the depth of inland is bigger that it of the coast, except the boundary region of Hunan and Jiangxi province, the depth of inland is about 40~50km deeper than the coast area. The lithosphere at the boundary of Hunan and Jiangxi is about 50km, which is equivalent to the marine area.The shallow depth of lithosphere has a big relationship with the uplifting of asthenosphere;③There are some discontinue high conductivity layer existing in the crust with the buried depth of 10~20km, it mainly distributes in the middle and lower curst of the resistivity value around dozens of ohms.④The numerical simulation displays that there is a big range of the uplifting asthnosphere region and high conductivity layer in upper mantle.⑤Numerical simulation shows that the high conduction layer in upper mantle is very extensively, the conduction layer in inland is extensive and consistent with the thickness of 50km. The layer in marine is partical distributed. The resistivity of high conduction layer in this profile is low. It is about dozens of ohms. The discontinuity of the high conduction layer can related to the uplifting asthenosphere. At the boundary of Jiangxi and Hunan, the uplifting asthenosphere causes the disappearance of high conduction layer and the thinness of lithosphere.⑥There is also an extensive region of asthenoshpere uplifting around Longyan and no exsitance of high conduction layer. In marine area, asthenoshpere uplifts seriously with 50km uplifting (standardized by inland lithosphere thickness). Analysis of numerical simulation also results that there are two faults extend exceed the crust with the depth over 30km, and a basement fault with the depth of 5km.The analysis and study in this paper has provided new reliance to the structure of mantle and crust in south China. The construction of electric model of Guidong-Xiamen profile has given significant meaning to the further study on deep electric structure and geotectonics.