Electrical structure characteristics of Longmen fault zone and its adjacent areas
Dai-Li XU1, Bao-Shan TANG2, Wen-Bo WEI3
1. Hubei Geological Survey, Wuhan 430034, China 2. Geophysical Exploration Party of Hubei Geological Bureau, Wuhan 430056, China 3. China University of Geosciences, Beijing 100083, China
Longmen fault zone is one of the most famous orogenic belts and seismic zones in the continental crust of China. In order to study the deep structure of Longmen thrust nappe belt and its relationship with the eastward escaping of material in the Tibetan Plateau, the authors completed four magnetotellurics profiles across the West Qinling orogenic belt, Songpan-Garze fold belt and the Sichuan basin, which included 80 broad-band magnetotellurics stations and 16 long-period stations. The electrical model diagram was obtained through two-dimensional and three-dimensional inversion. The model indicates that the Longmen Mountain fault zone is basically coincided with the electrical gradient zone in the depth less than 30 km. It means that the Longmen fault zone is a fault zone which is deep in the middle of the crust. Above the depth of 20 km, the distribution characteristics of the electrical structure in Songpan-Garze fold belt are complex and of low-conductivity, which is related to the complex surface structure. Below 20 km, the low conductivity is similar to that of the Longmen fault zone. It is inferred that high resistivity may be a reflection of the basement of the Sichuan basin, indicating that the Songpan-Garze fold belt pushed over Sichuan basin bounded by Longmen fault zone. It is concluded that the material migration under the Tibetan Plateau happened under the Songpan-Garze fold belt. The material escaped northeastward from Lixian to Dangchang, at the depth of 18km to 30km with the partial-melting.
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