Subducted Paleo-Tethyan Oceanic Slab beneath West Qinling, China Revealed by P-wave Anisotropic Tomography

Abstract

The subduction and closure history of the Paleo-Tethyan Ocean is of significant importance to the formation of the Alpine–Himalayan orogenic belt. However, in West Qinling, China, the evolution of the subducted Paleo-Tethyan oceanic slab in the mantle remains unclear. In this work, we determine high-resolution P-wave azimuthal anisotropic tomography of the crust and upper mantle beneath west Qinling by inverting newly collected local and teleseismic data. The local earthquakes are relocated by jointly using permanent and portable stations and weighted by their hypocentral errors during the inversion. Our model reveals a slab-like high P-wave velocity (V_p) anomaly below 300 km depth and significant depth variations of anisotropy in the upper mantle beneath the West Qinling orogen. By comparing with previous geophysical results and integrating with geological and geochemical findings, we interpret that this high-V_p anomaly is most likely the subducted Mianlue oceanic slab preserved in the upper mantle and the mantle transition zone since the early Mesozoic. Beneath the Songpan–Ganzi block and the Longzhong basin, low-V anomalies with weak azimuthal anisotropy suggest a vertical mantle upwelling at a depth of 120 to 200 km, providing positive buoyancy to the subducted oceanic slab and extends its stagnation duration in the upper mantle.

Keywords

seismic tomography / seismic anisotropy / Paleo-Tethyan subduction / West Qinling orogen / Tibetan Plateau

RIGHTS & PERMISSIONS

2025 Geological Society of China