The conductivity characteristics of Dagou-Luanjing middle and upper crust in Southern Ningxia arc structure

Abstract: In order to study the conductivity characteristics of Dagou-Luanjing middle and upper crust, the authors carried out magnetotelluric sounding work in the study area, and obtained the electrical structure model by the two-dimensional inversion method, which clearly reveals the typical electrical structure of Dagou-Luanjing: (1) The middle and upper crust shows the "chunky" structural style totally, and the authors infer that the conductivity of the corridor structure belt is relatively lower whereas the conductivity of the Qilian orogenic belt is relatively higher; (2) The low-resistivity zone caused by focal fracture of Haiyuan earthquake is neither steep like the strike-slip fault nor gentle like the thrust belt, but has both strike-slip and thrust characteristics; (3) The low-impedance and high-conductivity layers in the mid-upper crust of the study area intermittently exist, and show the structural style of deeper in the south and shallower in the north; it can also be inferred that these low-impedance and high-conductivity layers always reach their termination at the edge of the high impedance plots, or intersect the detachment layer under the thrust nappes; (4) A high resistance block exists in Qingshui River depression basin, which is likely to be an “island chain” paleouplift that was developed on the basin basement in Late Paleozoic and Early Mesozoic period,thus providing evidence for the tectonic movement of Yanshanian.