Crustal weakening by mantle upwelling in the southeastern Tibetan Plateau

Abstract The conspicuous eastward expansion of the Tibetan Plateau is evident and uncontroversial from geological surface expressions and remote sensing, but the mechanisms that cause it have remained enigmatic. The extrusion has been attributed to ductile deformation of a weak crust. This is consistent with the discovery of middle-lower crustal low (seismic)–velocity zones (LVZs), but the cause of crustal weakness and the origin and nature of the LVZs are debated, with competing hypotheses including channel flow from central Tibet, local fluid content, and mantle-derived processes. We present a high-resolution 3-D seismic attenuation (Qp) model of the crust and uppermost mantle in the southeastern Tibetan Plateau. Our results reveal high-attenuation anomalies in the middle-lower crust that overlap with previously imaged LVZs but extend across the Moho into the uppermost mantle. These anomalies correlate spatially with Cenozoic magmatism, mantle-derived helium isotope signatures, zircon Hf-isotopes, and major strike-slip faults. This suggests that the crust in the southeastern Tibetan Plateau is weakened from below, possibly by upwelling induced by tearing of the subducted Indian slab.