The lithospheric structure beneath the northeastern Tibetan Plateau and western North China Craton from S receiver function imaging and its implications for lateral growth of the plateau

Abstract

The mantle lithospheric structures beneath the northeastern Tibetan Plateau (NETP) and adjacent areas provide critical information about the role of the mantle lithosphere in the lateral growth of the plateau. In this study, we construct a comprehensive image of the lithospheric structure across the NETP and western North China Craton (NCC) using the S-wave receiver function method based on the dense seismic array of ChinArray II. We detect one or multiple negative conversions at the depth ranging from 80 to 200 km across most of the study region, which is associated with the seismic lithosphere-asthenosphere boundary (LAB) or mid-lithospheric discontinuity (MLD) within the lithospheric mantle. The main features include that the Beishan Block, West Qinling Orogen, and Qilian Orogen present a relatively shallow LAB at a depth range of 120–140 km, while the Longxi Basin and Alashan Block have the similar lithospheric structure with a deep LAB at depth > 150 km and some MLDs within the lithospheric mantle. We find that the Qilian Orogen in the western NETP overlying a thin mantle lithosphere has been significantly elevated, whereas the Longxi Basin in the eastern NETP with a thick mantle lithosphere lacks both high elevations and significant crustal thickening. It implies that the thick mantle lithosphere beneath the eastern NETP and western NCC likely prevents the plateau from invading the Longxi Basin, while the thin mantle lithosphere across the western NETP and Beishan Block favors outward growth of the Qilian Orogen. Our seismic images provide new insights into the lithospheric heterogeneities and their roles in the lateral growth of the Tibetan Plateau.