Limited Passive Lithospheric Underthrusting and Localized Crustal Thickening Beneath the Qilian Shan, Northeastern Tibetan Plateau: Evidence From Receiver Function Imaging

Abstract The Qilian Shan, located at the northeastern edge of the Tibetan Plateau (NETP), has undergone complex tectonic evolution and serves as an ideal region for studying the growth of the Tibetan Plateau. However, the mode of lithospheric deformation beneath the Qilian Shan remains a subject of debate. In this study, we use the common conversion point stacking technique with P and S receiver functions, calculated from waveform data recorded by a seismic array consisting of 153 broadband stations, to obtain images of crustal and upper mantle discontinuities beneath the NETP and adjacent Alxa block. Our findings reveal that the Moho depth beneath the NETP is greater than that beneath the Alxa block, with the deepest Moho located beneath the North Qilian area. A sudden decrease of ∼10 km in the Moho depth occurs from the North Qilian fault to the Alxa block. The lithosphere‐asthenosphere boundary is clearly identifiable in our data, showing a continuous, southward‐dipping interface from the Alxa block to the Qilian Shan. Integrating geophysical and geological results, we propose that passive underthrusting of the Asian Plate occurs beneath the Qilian Shan. This process, influenced by the strong obstruction of the Alxa block during the expansion of the NETP, leads to the accumulation of lithospheric mantle material and crustal thickening and causing the lithospheric mantle of the Asian Plate to bend and undergo southward underthrusting beneath the Qilian Shan.