Insights into Tibetan lower crustal composition through seismic velocity modelling

The Tibetan Plateau's lower crustal composition and rheology dictate the tectonic and surface deformation in response to the India–Asia collision. Yet, their spatial variations under the Plateau remain unclear. In this study, we forward calculated seismic velocities (i.e. V p and V s ) for three types of rocks presumed to constitute the continental lower crust. By comparing the simulated and observed velocities, we infer the current lower crustal composition of the Tibetan Plateau. The results show that W Tibet and Pamir is predominantly composed of eclogite, suggesting ongoing intense metamorphism. Our simulations reveal the presence of a weak felsic granulite layer in SE Tibet, potentially indicative of lower crustal flow. In contrast, the felsic component identified in eastern Lhasa is likely attributed to magmatic underplating. Our results further suggest that the lower crust of W Qiangtang and W Lhasa primarily consists of mafic granulite, indicating the likely preservation of Asian proto-rocks. Furthermore, by linking lower crustal composition to rheology, this study demonstrates how the crust has predominantly deformed in response to the India–Asia collision across the Tibetan Plateau.