LAUSR

Abstract The India-Asia Suture Zone (IASZ) records not only pre-India-Asia collision geological evolution, but also the surface uplift and growth history of the southern Tibetan Plateau. Recent studies from sedimentary and paleoaltimetric data within the IASZ reconstructed its surface uplift history and its geodynamical mechanism was proposed without any direct constraints. Post-collisional potassic magmatic rocks (PMRs) in the IASZ can provide unique opportunities to clarify deep crustal processes. Here we conducted systematically zircon U Pb age and Hf isotope, and garnet major and trace element analyses of the Saga PMRs in the western IASZ. The Triassic to Miocene inherited zircons are comparable to those of the central and southern Lhasa in terms of ages and eHf(t) values, suggesting that the PMRs in the IASZ might be sourced from the central–southern Lhasa through southward mid-lower crustal flow beneath the southern Tibetan Plateau. The occurrence of garnet in the gneissic xenolith of the Saga PMRs suggests crustal thickening in the IASZ before PMRs formation. Geochemical compositions of garnets reveal a heating and decompression event. We proposed that the Indian slab rollback resulted in the uprising flow and finally triggered melting of the thicken Asian crust to generate the Saga PMRs. This tectonic event also induced the extension and basin development in the IASZ. Our study provides direct evidence for the dynamic subsidence and uplift in the IASZ.