Crustal-scale Duplexing Beneath the North Qaidam Thrust Belts

As the largest intermountain basin inside the Tibetan plateau, the Cenozoic Qaidam basin has played important roles to accommodate formations during the Cenozoic Indo-Asian collision. To determine the crustal deformation mechanisms, we deployed magnetotelluric stations in the north Qaidam thrust belts (NQT), which is the northern margin of the Qaidam basin and bounds the southern Qilian Shan to the north. We conducted a three-dimensional subsurface geo-electrical modeling beneath the study area. The results show a <5 km conductive cover in the south of the NQT, this is consistent with Cenozoic sedimentation that has the thinnest thickness along the basin edges. Below the conductive deposition, the basin is imaged with high resistivity features, that extend to depths greater than 50 km. The results indicate a strong crust of the basin and argue against a channel flow. The mid- to lower crust beneath the NQT is significantly figured with relatively low resistivity layers. We suggest that the conductive mid- to lower NQT crust reflects a ductile shear zone that possibly induced a large southwest directed thrust duplex system. And the northeast dipping thrusts acted as a passive roof thrust of the duplex. Our results suggest a thick-skinned tectonic deformation across the NQT areas. By integrating shortening estimates and our geo-electrical model, we argue that the crustal duplexing accounts for the crustal thickening and accommodates the convergence between Tibet and North China.