Electrical resistivity variations of lithospheric mantle beneath the northern Tibetan Plateau with tectonic implications

Abstract

The northern Tibetan Plateau, including the areas north of Kunlun Shan, is characterised by a strapped basin–range system and major strike–slip faults; however, the surficial deformation, differs laterally. The collection of magnetotelluric (MT) data covering the northern Tibetan Plateau has made it possible to apply a three-dimensional isotropic inversion of these data for the entire study area. The plane area covered by MT sites is more than 700 × 700 km2 and the longest periods of most of these sites approximate or exceed 10,000 s. All of these aid in distinguishing the weak responses generated by deep anomalies in the lithospheric mantle. The three-dimensional inversion is applied to a subset of MT data, and it is observed that the full impedance data of most MT sites well-fit the responses of the final three-dimensional model. Two modes of relationship among the lithospheric mantles in the northern Tibetan Plateau are proposed. The moderate–low resistivity corridor indicates that the lithospheric mantle has a low viscosity, which is favourable for shortening at shallow crustal levels under a regional compression environment. Furthermore, the low-resistivity anomalies in the west Qaidam Basin and southwest Qilian Shan form a passage that may connect with weak materials in the lower crust of Songpan-Ganzi terrane through the Qiman Tagh range. The high-resistivity lithospheric mantle of east Kunlun Shan, east Qaidam Basin, and Alashan is dislocated according to the surface boundaries, indicating a face-to-face subduction below Qilian Shan. This represents the major dynamic model in the northern Tibetan Plateau.