The Study On The Deep Electrical Conductivity Structure Of The Heat-controlling Structure In Middle And Northern Of Guangdong

This article relies on China Geological Survey Bureau "Pearl River Delta and the sourrounding areas controlled thermal tectonic geological investigation" under the "Beibu Gulf Economic Zone and Pearl River Delta Environmental Survey Geological evaluation and the distinction project", to study the characteristics of deep fracture distribution and crust and upper mantle electrical shructure in Guangdong Province by using magnetotelluric sounding. We designed three section in southwest and northern of Guangdong(they are named line100,200and300), the location of100and200profile is located in the range of longitude111°-112.5°E, north latitude21.5°-22.5°N; the location of300profile is located in the range of longitude113°-116°E, north latitude23°-24°N. The profile oriented in an approximate east/west(WE) direction, crossing over the main fault of Guangdong Province, the structural trend is NNE. Through involving in a wild first-data collection personally and using broadband magnetotelluric instrument(V5-2000), three Magnetotelluric profiles,63points of broadband magnetotelluric points were obtained. For observing a unified data processing, Robust technology, human-computer interaction and static displacement correction method were used in this work. Analysis the orientations of principal electric axes, skewness, magnetic induction vectors, apparent resistivity and impedance phases section, as well as other relevant parameters, finally got the three sectional interpretation datum.By impedance tensor decomposition method for the research area’s best electric spindle analysis, combined with geological and geophysical data speculated the electrical spindle direction is NE30°-60°. The skewness underground media was calculated and the research results show that the shallow area has good two-dimensional nature, the deep tectonic structural is complex, the performance of the three-dimensional nature. Each curve determines polarization mode were distinguished through the polarization characteristics of measuring point. Distortion and static shift measuring point were corrected static effect. Compared and analyzed magnetotelluric inversion methods, we selected nonlinear conjugate gradient method(NLCG) for two-dimension inversion. Connecting with the300profile geological data, the TE, TM and TE&TM joint2-D inversion model were analyzed and the TM model is considered the best inversion model in this case. Through some experimental researches, we got the suitable regularization to participate in the inversion. Combining with regional geophysical and geological data, the previous study of geology, geophysics and geothermic, we investigated the features of fault in research area, crust and upper mantle electronic structure features and its dynamic, and the relationship between distribution characteristics of the surface hot spring and deep thermal condition respectively.According to data inversion results contrast regional tectonic analysis, the electric gradient and distortion zone are consistent with deep fault zone, we determine6NNE fault zones, which are the east zone of Wuchuan-Sihui fault, the west of Wuchuan-Sihui fault, Enping-Xinfeng fault zone, Heyuan fault zone, Zijin-Luobo fault zone and Lianhuashan fault zone, and we analyzed the characteristics of the trend, cutting depth, tendency and influence area of each fault zone. The thickness of crust and upper mantle in study area changes is larger. All the sections have the characteristics of being thin in the east and thickness in the west, and the crust and upper mantle in the coast area are pretty thick, away from the coastal inland thickness is larger. For the Moho, the mean value is29-43Km of100and200profiles in southwest of Guangdong, and suggesting a depth of50-70Km lithosphere; Northern area300sectional Moho depth30-55Km,lithosphere thickness90-110Km. Three of the transverse cross section showed obvious inhomogeneity on lateral, and there are continuous low resistance area at the bottom which the characteristics have significant difference with its upper stratum. The internal electrical structure of lithosphere in research area on the longitudinal can be divided into three main layers. The first layer is a surface zone of a low resistivity and possibly is the Cainozoic Era deposit formation; The second layer is a high resistivity zone which is cut by deep fault, and there is a discontinuous conductive layer; The third layer below the Moho showed a large area of low resistance layer. Characteristics of the underguound crust-mantle area analysis, suggests that the Pacific plate to the Eurasian plate subduction oceanic lithosphere sinking, rising hot mantle material and resulting in the southeast coastal areas with high thermal state of the crust and mantle.