A Study On Crust/mantle Electrical Structure Characteristics And Its Dynamics Background In Southeastern Of South China

For a long period of time, the crust/mantle structure of south China, the connection betweencrust/mantle structure and tectonics, the distribution characteristics of granite and its formation arealways the hot researches; there have been no definite answers yet. In this paper, we carried outthe area three-dimensional magneto telluric observational studies supported by“SinoProbe-DeepExploration in China”SinoProbe02-04-02subject in southeast of south China and got somemeaningful results, wishing to have the mentioned problems settled to some extent.The location of research area is between east longitude113°-121°, north latitude23°-29°, theprofiles go across the cathaysia block and the southeast coast block, their directions are NWW,perpendicular to the direction of main structure, the NNE direction. Using broadbandmagnetotelluric instrument (V5-2000) and long-period magnetotelluric instrument (LEMI-417),we have got11Magneto telluric profiles,413points of broadband magnetotelluric points and98long-period points. This paper mainly investigates the190points of broadband magnetotelluricand46long-period points in the5south profiles.In field observation, we got a lot of high quality field data through proper migration for points,flexible parameter selection, rigorous operations and installation of reference station. We used theRobust technology, remote reference technology, human-computer interaction and staticdisplacement correction respectively to suppress the noise and attempted to join the broadbandmagnetotelluric data and long-period magnetotelluric data together. We got the information aboutlongitudinal conduct, polar plots and2D irrelevance of the research area, the analysis suggest that:southeast part of south China presents2D features, in some areas the3D features are moreobvious; the direction of main axis of optimal electric property is NE; the main direction ofstructure is NE and some are NW, near SN or near EW; combining the real part of vector with2Dstructure profile of electrical property, the position, size and direction of the fault can be easilypredicted. The studies suggest that the main direction of fault zone is NNE.We evaluated the polarization mode for apparent resistivity curve of each point and done theTE, TM and joint inversion. Then we got five magnetotelluric2D electronic structure profiles.Based on the previous study of geology, petrology, geophysics, geochemistry and geothermic, weinvestigated features of fault in southeast of south China, the division of tectonic units,crust/mantle electronic structure features and its dynamic, distribution characteristics of graniteand its formation and deep thermal condition respectively. The research results are follows:(1) According to the real part of induction vector and five magnetotelluric2D electronicstructure profiles, we determine8NNE fault zones, that are Wuquan-Jian fault zone(F1),Ganjiangfault zone (F2), Yangjian-Jinhua fault zone(F3), Heyuan-Shaowu fault zone (F4), Aomen-Jianyuanfoult zone(F5), Lishui-Haifei fault zone(F6), Fuan-Haifeng fault zone(F7), Changle-Zhaoan faultzone, then we analyze the characteristics of each fault zone.(2) According to2D electronic structure features of5profiles and the fault zones wedetermined, based on the previous research results, we divide the research area into Huaxia block and southeast coast block. The Huaxia block consists of Wugong-Zhuguang fold zone, Wuyishanuplift area and northeast Guangdong depressed area.(3) The crust/mantle thicknesses are fluctuant, the crust/mantle in the coast area and inlandare pretty thick, the average thickness of lithosphere is more than100km, formation ofcrust/mantle in coast area is related to the interaction between the Pacific plate and Eurasian plate.The formation of crust/mantle inland is related to Collision convergence effect and Orogeny effect,so the thickness of crust/mantle is small in the profile. And there is obvious asthenosphere uplift.The direction of uplift zone is NE, asthenosphere uplift closely relate to the delamination thinningdense of southeast region of south China.(4) The granite in southeast of south China during different time period is widespread, thereare two obvious granite zones, the NNE Mesozoic and cenozoic granite zone, EW-trending granitebelt. In this paper, we analyze the horizontal and vertical features of granite distribution, based onthe features of granite distribution, redistrict the granite distribution, and try to analyze thebackground information about the formation of granite in each area.(5) We analyze the relationship between the electrical conductivity of crust/mantle andtemperature, and discover that the electrical conductive in the deep crust/mantle is related totemperature directly, high electrical conductivity corresponds to high temperature. In this case, weanalyze the thermal state of deep crust/mantle according to the features of electrical conductivity.The results suggest that the thermal state of deep crust/mantle obtained from the electricalconductivity is accurately and intuitively, consistent with that obtained by other methods.