High-resolution lithospheric structures of the Qinling-Dabie orogenic belt: Implications for deep subduction and delamination of continental lithosphere

Abstract

The Qinling-Dabie orogenic belt was formed during the collision between the North China Craton and the Yangtze Block. A large volume of the high-pressure (HP) and ultra-high-pressure (UHP) metamorphic rocks are exposed in the eastern Dabie Mountains. In order to better understand the collision processes and the exhumation mechanism of the HP/UHP rocks, we process ambient noise data recorded at stations in the Qinling-Dabie orogenic belt and surrounding areas to extract broadband Rayleigh wave dispersion curves at 8–95 s periods. Using these dispersion curves, we construct a high-resolution 3-D shear wave velocity model of the Qinling-Dabie orogenic belt and surrounding regions. Our 3-D model reveals high velocities in the uppermost mantle beneath the western Dabie Mountains and also beneath the western Qinling Mountains, suggesting the presence of remnant continental lithosphere from the past continental subduction. Low velocities in the lower crust and uppermost mantle beneath the eastern Qinling and eastern Dabie are imaged, suggesting the continental lithosphere delaminated in the past. Our 3-D model supports a two-stage exhumation model of the HP/UHP rocks in the eastern Dabie orogenic belt, in which HP/UHP rocks were first exhumed to the mid/lower crust in the first stage and were then further exhumed to the surface under the driving force of the upper mantle upwelling induced by the lithosphere delamination.