Constraints on the process and mode of the Paleo-Asian Ocean closure from the lithospheric conductivity structure of the south-eastern Central Asian Orogenic Belt

The Paleo-Asian Ocean eventually closed along the Solonker Suture Zone during the Late Permian and Early Triassic, before the collision between the Siberian Craton and the North China Craton (NCC) formed the eastern Central Asian Orogenic Belt (CAOB). In this paper, Magnetotelluric (MT) profile data across the south-eastern CAOB and the northern margin of the NCC are explored to image the two-dimensional resistivity structure of the region. According to the resistivity model, a north-dipping conductive layer to the north of the Xilinhot fault and a south-dipping conductive layer to the south of the Linxi fault are revealed. The two conductors are interpreted as evidence of the late-stage low-angle bidirectional subduction of the Paleo-Asian Ocean, which constrains the northern and southern deep boundaries of the Solonker Suture Zone. Another couple of mantle conductors with opposite dipping angles are revealed under the Solonker Suture Zone and Bainaimiao Belt, which are interpreted as evidence of the early-stage high-angle bidirectional subduction of the Paleo-Asian Ocean. Compared with the results from previously reported MT profiles in this area, the subduction angle be-comes more gentle from west to east. The difference of convergence rate between the NCC and the Siberian Craton is considered to be the major cause of the closure difference along the strike. The northern margin of the NCC has a conductive lower crust, which may result from the magma underplating or crust-mantle decoupling, as it is imaged to be connected with the south-dipping conductive layer beneath the Solonker Suture Zone.