Electrical structure of middle and upper crust beneath the Minshan uplift zone and central section of the West Qinling orogenic zone

The Minshan uplift zone and the central West Qinling tectonic belt are located in the eastern margin of the Tibetan plateau, part of the north-south seismic belt, where GPS velocity discontinuity decays and converts, so receiving much attention of domestic and foreign geophysicists. Study of the deep structure and spatial distribution characteristics of boundary fault zones in this region is important for the understanding of the Tibetan plateau's uplift mechanisms and the causes of strong earthquakes there. This study is based on two magnetotelluric (MT) sounding profiles (SG-WQL-L1 and SG-WQL-L2) with small measurement spacing, which pass through the two zones aforementioned. Data processing and analysis include calculation of the electric strike and 2D skewness of the area using phase vector decomposition, and processing the original data according to the electric strike. The NLCG 2D inversion is performed on apparent resistivity and phase data of TE+TM modes, obtaining resistivity structure models along the profiles. The results of inversion show that low-resistivity layers are present at depth beneath the Barkam block, which contacts with the upper crust low-resistivity body of the Minshan uplift at depth. The Minjiang and Huya faults are controlled by the detachment beneath the Barkam block and Minshan uplift, of which the angles become steeper to the east and dislocation formation occurs at depth. The focal depths of history earthquakes reveal that the Huya fault zone is the seismogenic fault in Cenozoic but the Minjiang fault zone is not. The structure characteristics of the stratified vertically and the blocking laterally mid-upper crust are revealed by the resistivity profiles of the central section of the West Qinling orogenic zone. The boundary faults of subblocks in the study area and the low-resistivity layers which are present at the bottom of upper crust are converging at depth. The subblocks and the active fault zones bounding the subblocks are likely responsible to the decay and conversion of GPS velocity discontinuities. Thermal mantle flow in the Tibetan plateau shifts toward east along the asthenospheric channel, and then induces upper crust of the eastern Bayan Har block to move toward east along the low resistivity layer in the mid-upper crust. Due to the obstruction of the rigid crust of the Motianling block, poly-stage overthrusting and folding happened in the crust of the plastic Minshan block, leading to the uplift of the Minshan Mountains, while sinistral slip of the Minjiang fault and Huya fault accelerated the Minshan uplift.