Post-collisional K-rich
volcanic rocks (KVRs) can pro
vide an opportunity to constrain the architecture of the lithosphere and the mechanisms of plateau uplift. Howe
ver, their petrogenesis and geodynamic setting remain in dispute. Lithium concentrations and isotopic compositions of 87 potassic, ultrapotassic and Mg-rich potassic
volcanic rocks (PVRs, UPVs, and MPRs, respecti
vely) in SW Tibet, along with new Pb–Sr–Nd isotope data and wholerock analyses, are used to constrain their mantle source and genesis. These rocks are characterized by
very similar δ7 Li
values: PVRs
vary from −4.9‰ to +3.2‰, UPVs from −3.9‰ to +1.7‰, and MPRs from −1.2‰ to +3.5‰. They can be classifified into two groups: Group I (19 out of 87 samples) with hea
vier δ7 Li
values (+1.0‰ to +3.5‰) similar to those reported for mid-ocean-ridge and ocean-island basalts (MORBs and OIBs, respecti
vely), and Group II (68 out of 87 samples) with lighter
values (−4.9‰ to +1.0‰) similar to those of Indian lower crust. These
variable isotopic compositions may record the isotopic signature of the early-middle Miocene subcontinental lithospheric mantle (SCLM). This paper demonstrates the existence of isotopically light mantle domains beneath the Lhasa terrane, which were ascribed to the interaction with flfluids/melts deri
ved from the subducted Indian lower crust. The modeling cur
ves of Indian lower crust with a metasomatized mantle composition fully account for compositional
variations in the PVRs, UPVs, and MPRs. They were generated by the partial melting of SCLM, which was metasomatized by flfluids/melts deri
ved from the subducted Indian lower crust (ca. 4–14%, ca. 4–10%, and ca. 6–10% for the PVRs, UPVs, and MPRs, respecti
vely). The Li isotopic data indicate that the Indian lower crust was subducted beneath the central Lhasa subterrane, and this sheds new light on the formation of the Tibet Plateau.
© 2019 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.