Contrasting crustal deformation mechanisms in the Longmenshan and West Qinling orogenic belts, NE Tibet, revealed by magnetotelluric data

Abstract

The northeastern margin of Tibet is the youngest risen part and key area for understanding the growth mechanism of the Tibetan Plateau. New broadband magnetotelluric (MT) data are conducted at the conjunction of the Longmenshan and West Qinling orogenic belts in NE Tibet. The preferred resistivity model obtained using 3-D inversion method shows a dramatic resistivity contrast from the Sichuan Basin (SB) to the West Qinling Orogenic Belt (WQOB). Beneath the SB and Longmenshan Orogenic Belt (LMSOB), several low-resistivity zones are distributed in the upper crust underlain by an intact resistive lower crust, indicating the upper crustal deformation is responsible for the uplift of the LMSOB. While to the north, a prominently conductive lower crust is observed, favoring the ductile deformation of the weak lower crust plays a significant role in the crustal thickening of the WQOB. Therefore, we suggest contrasting crustal deformation mechanisms work in the LMSOB and WQOB, and diversified crustal deformations together contribute to the marginal growth of the plateau. Moreover, combining with other studies, we propose the deep conductive bodies beneath the WQOB would be induced by the hot upwelling related to the asthenospheric flow from the plateau.