The crustal electrical structure of a tectono-magmatic rejuvenated craton: Insights from magnetotelluric data of the northwestern Qaidam Basin, northern Tibetan Plateau

The Qaidam Basin is a tectono-magmatic rejuvenated craton that plays a key role in the deformation of the northern Tibetan Plateau caused by the far-field effects of the India-Asia collision. However, the deformation mechanism of the crust and upper mantle beneath the basin is still elusive to date. Here we present an electrical resistivity model of the crust and uppermost mantle in the northwestern margin beneath the Qaidam Basin (QB) from magnetotelluric (MT) data. The MT data were collected along a -300 km long profile and inverted using the MARE2DEM code with the OCCAM algorithm. From the model, four major conductors were revealed in the lower crust of the Qaidam Basin and the crust-mantle transition zones of the Qiman Tagh thrust belts (QTT) and Suganhu Basin, respectively. Constrained by the laboratory measurements, the conductors (-2-10 omega m) beneath the western QB can be explained by a small amount of saline fluids (-0.2%-2%) derived from devolatilization reactions, which indicates ductile deformation of the lower crust of the Qaidam Basin. The upper mantle con-ductors beneath the Qiman Tagh and Suganhu Basin may be related to asthenospheric upwelling caused by the partial removal of the lithosphere at different stages in the central and northern Tibetan Plateau, respectively. These electrical features suggest that the Qaidam lithosphere has experienced devolatilization, partial melting, delamination of the lower crust, and upwelling of the asthenosphere, resulting in a tectono-magmatic rejuve-nated craton.

Automated summary

In this study, we provide an electrical resistivity model of the crust and uppermost mantle beneath the northwestern margin of the Qaidam Basin using magnetotelluric (MT) data. We identify four major conductors in the lower crust of the basin and the crust-mantle transition zones of the Qiman Tagh thrust belts and Suganhu Basin. These conductors are associated with devolatilization reactions and asthenospheric upwelling, indicating ductile deformation and tectonic-magmatic activities in the Qaidam lithosphere.