Tectonic transition revealed by upper mantle heterogeneities and anisotropy of the SE margin of the Tibetan Plateau: Insights into the Cenozoic intraplate volcanisms

The SE margin of the Tibetan Plateau is a key channel for understanding the plateau's evolution. However, the links between mantle dynamics, surface deformation, and associated intraplate volcanism remain elusive. Here, 3D radially anisotropic seismic structures of the upper mantle beneath the SE margin of the Tibetan Plateau are presented based on adjoint waveform tomography using dense arrays. The seismic image shows a prominent tectonic transition along 26 degrees N, characterized by strong heterogeneities. In the north of 26 degrees N, lithospheric delamination is revealed by high-velocity anomalies between the Tibetan Plateau and the Yangtze Craton at the 150-250 km depth, which may drive the early Cenozoic potassic volcanism. In the south of 26 degrees N, asthenospheric flow is suggested by significantly low velocity and positive radial anisotropy at the uppermost mantle, which probably accounts for the late Cenozoic sodic volcanism. We propose that such upper mantle dynamics shape the surface expression of plateau uplift and intraplate volcanism.Plain language summary: The mechanism controlling the growth and volcanism of the Tibetan Plateau remains ambiguous. We present clues from subsurface structures using earthquake seismology. We observe strong heterogeneities of velocity and anisotropy in the upper mantle of the SE margin of the Tibetan Plateau. The results suggest that lithospheric delamination and asthenospheric flow control the generation of the early Cenozoic K -rich volcanism and late Cenozoic Na-rich volcanism, respectively. Our study indicates that tectonic transition might exist in the subsurface of the SE margin of the Tibetan Plateau.