Crustal and upper mantle electrical structure and uplift mechanism of the Liupanshan orogenic belt in the NE Tibetan Plateau

The Liupanshan orogenic belt (LOB) is located in the convergence zone of the NE Tibetan Plateau and the Ordos Block (OB). A crustal and upper mantle structure study of the LOB is vital for providing a deeper understanding of upper crustal shortening and orogenic uplift in the NE Tibetan Plateau. In this study, we utilized broadband magnetotelluric (MT) data at 122 stations that cross the LOB to determine an optimal electrical model by comparing the models obtained from 2D and 3D inversions. Several revealed upper crustal resistivity boundaries are connected with a conductive layer in the middle-lower crust by our model, which acted as a decollement system for the eastward thrusting of the upper crust. Our model also showed that a large-scale westward-dipping high-resistivity body developed beneath the western margin of the OB, which suggests that the thin and rigid crust in the OB was pushed into the thick and soft block in the NE Tibetan Plateau, which indicates that a double Moho might appear beneath the LOB and its adjacent areas. A coherent U-shaped medium-lower resistivity anomaly zone (UMLRZ) developed at depths of approximately 60–80 km, which is shown in our model and may be related to partial melting or a hotter mantle. Combined with previous research results, we suggest that the present crustal structure and topography in the LOB and its adjacent areas are probably controlled by two main stages of activity: the far-field effect of the oblique subduction of the Pacific plate toward the Asian continent plate and the collision between the Indian and Eurasian plates. Owing to the existence of the ductile zone UMLRZ, the LOB easily incurs gravitational collapse and cannot increase indefinitely, which is the key factor responsible for the relatively gentle topography of the transition zone between the LOB and OB.