| Yinchuan Graben and Helan Mountain in Qinghai-Tibet block the combination, the Ordos block and the block of Alashan.The special geotectonic situation,strong neotectonic movements and strong deep hydrothermal activity have contributed to Yinchuan Basin geothermal resources form the regional geological tectonic setting.This paper, on the background of Yinchuan Graben and Helan Mountain geological and geophysical structure, using the magnetotelluric sounding method, by studying the electrical structure of magnetotelluric sounding profile of which cross the Helan Mountain fault zone and the Yinchuan rift zone, and combining with Geophysical and geological data discussed the deep fracture in the Helan Mountain and the Yinchuan Basin in deep extension of the situation and the boundaries of tectonic unit, and expound the Alashan southeast edge uplift’high resistance block, Yinchuan Basin’low resistance and Helan Mountain electrical structures on the earth’s crust type. We can forecast the geothermal area by combining with the relevant data of Yinchuan area. According to the research above, this paper prospect some of new understandings about the deep electrical structure and geothermal exploration in the study area:(1) Combining the deep structure of the Yinchuan fault basin and the Helan Mountain, this paper established a few farming models, and conducted the forward numerical simulation and inversion calculation, analysised of the TE、TM and TE+TM model inversion effect, thus verified that the magnetotelluric looking for low resistance block effect is obvious.(2) Analysising the tensor impedance data, paper got the Mohr’s circle and two dimensional deviation,whitch the results are consistent, and overall reflect the measurement area is given priority to with2D regional structure; by using the impedance tensor decomposition method to analyze the electrical spindle, understood the optimum azimuth, shows that2D inversion interpretation should be arranged along the section direction.(3) According to electrical diagram analysis,it can be divided into:Bayan haot basin, Alashan southeast margin, Helan Muntain fault zone, Yinchuan rift zone, west margin of ordos transitional zone.and can Preliminarily consider that Alashan southeast edge uplift is given priority to with high resistance and better electrical layers; The centralsection and superficialpart of the Helan Mountain area characterized by relative high resistance, bu the deep part show a low resistance; The whole Yinchuan graben show a low resistance, and the fault development, formation and broken, water filling may be the cause of resistivity reduce. The overall presentation of Yinchuan fault basin is a Low block model witch the west is shallow bu the east is deep, meanwhile,the upside is broad and the underpart is narrow; Ordos transitional belt of the western margin electrical structure characteristics on the longitudinal from shallow to deep performance for low-high-low-high configuration, electrical is stratified.(4) According to the structure diagram and the geological profile analysis shows that the Helan Mountain XiLu fault zone is the boundary faults of ordos massif and Alashan block; Yellow River fault zone is obvious difference in electrical tape. The both sides of the fault zone on the electrical characteristics of the difference is obvious on the electrical diagrams; The Yellow River fault zone and the Helan Mountain foothill fault zone is boundary faults of Yinchuan Basin respectively.(5) The electrical structure of Ningxia section may be the result of the interaction between Alashan block and ordos block.(6) Combining Yinchuan Basin geothermal data, geological data and magnetotelluric data, this paper analyzed the regional geothermal formation, discussed the influence of the basal structure and the active faults on the geothermal resource distribution, delineated the northwestof Yaofu town for geothermal area. |
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