Electric Structure of Crust and Upper Mantle Along the Xilinhot‐Dongwuqi Profile in Inner Mongolia

In order to provide the geologic background for exploration, mineral prediction and evaluation over the Hegen Shan around Dongwuqi, ultra-broadband and long-period magnetotelluric (MT) data were collected at 26 sites with spacing from 3 to 6 km along a 100 km profile. Through processing by robust transform and cross reference techniques, the resistivity and phase curves, skew angles and regional strike were analyzed qualitatively. And then the 2D NLCG inversion was performed to obtain the electrical structure of crust and upper mantle at depth of 120 km along the profile for the first time. The research results show that there are four structure units, whose structures of crust and upper mantle are very different from each other, with the boundary of the Hegen Shan and the Xilinhot suture zones across profile. The high-conductivity layer south of the Xilinhot plate suture zone is at depth about 25 km below the earth surface, with double-layer low conductivity geologic bodies. The high-conductivity layer north of the Hegen Shan plate suture is at depth about 15 km, and the Moho depth is about 50 km. No high-conductivity layer is observed between the two plate sutures, where the curst is of high resistivity as a whole. The Hegen Shan plate suture is controlled by two 15 km-wide faults in lithosphere locally with south dipping high-conductivity bodies and uplifted mantle. The base of crust is about 25 km deep, and the high-conductivity layer in upper mantle is at depth of 55 km. The width under cover layer of the Xilinhot suture is about 6 km, connected with the high-conductivity layer in crust. There are channels for upwelling of crust and mantle derived materials under the sutures. The secondary fault systems controlled by sutures are favorable conditions for aggregation, migration and mineralization, forming a metallogenic prospect.