| Xianshuihe fault zone is located in the eastern margin of the Tibetan Plateau and the northwestern part of Sichuan Province,with a total length of about 400 km.It starts from the eastern valley of Ganzi,Sichuan Province in the north,extends southward through Luhuo,Daofu and Kangding,and dies in the vicinity of Gongyi Sea in Shimian County.The NWSE trending and NE protruding arc distribution,together with the Longmenshan fault zone to the east and the Anninghe-Xiaojiang fault zone to the south,formed a huge "Y" shaped fault system,which jointly influenced the formation and evolution of the Tibetan Plateau.To identify fault zone of deep crustal structure of electrical characteristics and depth structure response relation,based on the national project "balyanlkalla north rim and east edge of large faults of regional geological survey,using the method of magnetotelluric sounding(MT)in fresh water river fault zone daofu-kangding period was carried out by two line a total of194.5 km of the data collection work,After fine data processing and analysis,impedance tensor GB decomposition and phase tensor analysis,the structural dimension characteristics and electrical main axis direction of the study area were obtained.Different inversion modes and parameters were compared and analyzed.Finally,two-dimensional nonlinear conjugate gradient(NLCG)inversion under the regularization factor of 10 and TM mode was selected.The results reveal that the study area has good two-dimensional electrical structure characteristics on the whole,and the deep part presents complex structural characteristics.Combined with regional geological and other geophysical data,the results are as follows:1.According to the MT inversion results,it is shown that the upper crust presents high resistivity anomaly,and the middle and lower crust is characterized by the development of large scale low resistivity anomaly,which is divided into transverse blocks and distributed in vertical layers.The upper crust of Xianshuihe structure in the Yajiang tectonic belt is mainly characterized by middle-high resistance bodies.The middle-lower crust of the Yajiang tectonic belt and Xianshuihe structure are widely developed with large scale of high inner crust conductors,while the Danba tectonic belt and the Kangding tectonic belt are mainly developed with high-resistance bodies.In the places where faults are developed,they generally show the characteristics of low resistivity,which indicates that the development of high conductors is not uniform and is closely related to fault activities.2,comprehensive analysis of the inversion results show that the fracture development,within the scope of the section in the study area is characterized by low resistivity anomalies or electrical gradient zone,and is given priority to with Angle of vertical deep fracture,fracture extension ending more than in the upper crust,east north of fracture structure tend to give priority to,a few tended to Nancy,shallow fracture Angle steep,deep into the gradient,The main deep and large faults are the boundary faults of each tectonic unit,which play a leading role in other tectonic activities in this area.The faults developed in the Xianshuihe structural belt are flower-like,and the main fault of Xianshuihe is a supercrust fault with cut depth on Damoho surface.3.The formation of high conductors in the upper crust of the study area may be related to the factors such as heat generation during the fault strike-slip extrusion process,the pore enlargement caused by rock fragmentation and filling by water(salt)fluid,etc.The large scale of high conductors in the middle and lower crust may be formed by the participation of salt(water)fluids in the partial melting of the lower crust,so that the development scale and range of high conductors are further expanded.When encountered with rigid blocks,the high conductors flow upward or downward along the fault branches,thus causing crustal thickening and surface uplifting deformation. |
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