Lithospheric electrical structure between the Erguna and Xing'an blocks: Evidence from broadband and long period magnetotelluric data

The Central Asian Orogenic Belt (CAOB) is the largest accretionary orogen on Earth, and its evolution has been controversial for a long time. Northeast China and adjacent regions form the eastern portion of the CAOB, which is an important area for exploring the tectonic evolution of both the Northeast Asia and the CAOB. The Erguna and Xing'an blocks are two micro-blocks in the west of Northeast China. The magnetotelluric (MT) method can study subsurface electrical structures. A dense broadband and long period magnetotelluric (MT) profile across the collision belt of the two blocks has been completed. Based on the results of data analysis, a three-dimensional (3-D) resistivity model of the crust and upper mantle has finally been obtained. The MT results show that the Derbugan Fault is not a suture zone, whereas the Xinlin-Xiguitu Fault is considered the boundary of the Erguna and Xing'an blocks by westward subduction. The conductive bodies in the middle-lower crust of the Erguna and Xing'an blocks may have been formed in an extensional environment and imply that the crust is weak. The collision belt includes a prominent high-conductivity anomaly from the lower crust to the upper mantle and indicates the existence of mantle upwelling associated with probable delamination.