Electrical structure of the middle Qilian Shan revealed by 3-D inversion of magnetotelluric data: New insights into the growth and deformation in the Northeastern Tibetan Plateau.

The Qilian Shan is located along the northeastern margin of the Tibetan Plateau, which is a key area for studying the growth and expansion of the Tibetan Plateau. There have been several geodynamic models developed to explain the deformation pattern of the Tibetan Plateau extending to the northeast, but they remain controversial. The magnetotelluric (MT) method can study subsurface electrical conductivity and rheological properties. A dense broadband and long period magnetotelluric (MT) profile across the middle Qilian Shan has been completed. The MT profile starts from the northeastern margin of the Qaidam Basin, crosses the Qilian Shan and Hexi Corridor, and finally reaches the southwestern margin of the Alashan Block. Based on data analysis results, a three-dimensional (3-D) resistivity model of the crust and upper mantle has finally been obtained. The MT results show that a relatively low resistivity zone exists at the bottom of the upper crust of the Qilian Shan, features as an intracrustal decollement, which indicates the decoupling deformation between the upper and lower crust. The isolated conductive bodies in the middle-lower crust of the Qilian Shan may have formed during the primary stage of plateau growth, suggesting that there may be no existence of the middle-lower crustal flow beneath the Qilian Shan. The Alashan Block lithospheric mantle may have partly underthrust southward the Northeastern Tibetan Plateau. The Tibetan Plateau may have grown and expanded northeastward across the Hexi Corridor to the Heli Shan Fault. • Lithospheric electrical structure along a profile across the Qilian Shan was obtained from 3-D inversion of MT data. • There may be no crustal flow. Alashan Block may have partly underthrust the Northeastern Tibetan Plateau. • Tibetan plateau may have extended northeastward across the Hexi Corridor to the Heli Shan Fault. [ABSTRACT FROM AUTHOR]