Seismic evidence for lithospheric delamination-driven mantle upwelling beneath the northern Tibetan Plateau

How the Tibetan Plateau grew farther north from the India-Asia collision boundary has profound implications for understanding the mechanics of continental deformation and accretion. Lithospheric delamination and associated mantle upwelling have been inferred beneath the northern Tibetan Plateau, supported by widespread active magmatism coeval with the rapid uplift of the Hoh-Xil Basin since the Miocene. However, in-situ seismic constraints have been limited due to the region’s inaccessibility. In this study, we combine ambient noise tomography and shear wave splitting analysis to investigate the structures of the crust and upper mantle, using recently available data from linear seismic arrays across the Hoh-Xil Basin. Our three-dimensional S-wave velocity model reveals a partially molten crust in the Hoh-Xil Basin, manifested as widespread low-V_S anomalies, which is spatially correlated with strong uppermost mantle low-velocity anomalies and young exposed magmatic rocks. Our new shear wave splitting measurements across the Hoh-Xil Basin reveal significant E-W-oriented splittings reflecting variability in mantle dynamics, as indicated by the estimated anisotropy depth of 150−200 km and the alignment closely with the absolute plate motion of the Tibetan Plateau. The delay times of these splittings peak at ~1.8 s in the northern Qiangtang Terrane and gradually decrease as SKS travel-time residuals increase toward the northern margin of the plateau, coinciding with the northward migration of young magmatism. These findings provide compelling evidence for the mantle upwelling beneath the Hoh-Xil Basin driven by extreme lithospheric thinning, suggesting that the plateau grew northward through lithospheric mantle removal and subsequent magmatic accretion.