Crustal isostatic state and lower crust delamination beneath the Qinling Orogenic Belt: Constraints from receiver function imaging

The Qinling Orogenic Belt (QOB) is an important tectonic belt in eastern Asia, which is believed to have been formed by the intracontinental collision between the North China Craton and South China Block. By analyzing radial P-wave receiver functions recorded by 239 broadband stations, we investigate the crustal thickness and Vp/Vs ratio maps under the QOB and its adjacent regions using the H-k and common conversion-point (CCP) stacking methods. The crustal thickness (H) and Vp/Vs ratios (k) showed significant lateral variations. The assessment of crustal isostatic compensation reveals that the topography of the Dabashan and central QOB are compensated by crustal thickness, although the later may not be fully compensated. The crust of the western and eastern QOB are possibly in a non-Airy-type isostasy state, and the low-density uppermost mantle may play an important role in compensating their elevations. The Dabashan and the region to the south have thick crustal thickness and high Vp/Vs ratios, while the east QOB have thin crustal thickness and low Vp/Vs ratios. The CCP images reveal two strong positive amplitudes at depths consistent with the Moho interface near the Ankang fault. These observations indicate complex lower crustal structure and suggest the existence of eclogitized lower crust beneath Dabashan and lower crust delamination beneath east QOB. We also observe a continuous area with thick crust and high Vp/Vs ratios that covers the Dabashan, Hannan-Micang Dome, Shennong-Huangling Dome and their surrounding regions. This area shows consistency in location with a rapidly uplifted area since approximately 15 Ma, which-with other geological studies-implies the asthenospheric flux from the Tibetan Plateau. The asthenosphere flow may have eroded the lithosphere beneath the Dabashan and promoted the lower crustal eclogization. (c) 2021 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.