Far-field effect of underthrusting Greater Indian slab on lithospheric mantle beneath the eastern Tibetan Plateau Available to Purchase

The India-Asia collision ca. 55 Ma and the continued convergence since then are documented to have transformed the compositional heterogeneity of the subcontinental lithospheric mantle beneath southern Tibet. However, it is unknown if this process may have also been responsible for the younger magmatism farther inland in eastern Tibet. To answer this question, we studied potassic-ultrapotassic rocks of phlogopite-bearing subcontinental lithospheric mantle origin in both the northern and southern fields in the eastern segment of the Qiangtang block. The locations of these potassic-ultrapotassic rocks align with juvenile and ancient crustal domains, respectively, identified using zircon Hf-isotope mapping of Cenozoic granitoids. Furthermore, these locations also correspond well with variations in mantle P-wave (V_P) seismic tomography. Taken together with the literature data, we examined early-crystallized clinopyroxenes and their hosting melts from the potassic-ultrapotassic rocks. Our results show that the southern potassic-ultrapotassic rocks have traits of an older, isotopically enriched, and more carbonated subcontinental lithospheric mantle, whereas the northern potassic-ultrapotassic rocks are younger, isotopically depleted, and less carbonated. With magmatic-tectonic records, seismic structure, and plate reconstruction all considered, we conclude that the subcontinental lithospheric mantle beneath the southern field experienced intensive metasomatism from Greater Indian slab−derived carbonatite melts, while that beneath the northern field was preferentially affected by slab rollback−related upwelling asthenosphere beyond the slab edge in the Eocene. These observations point to a much greater impact of the underthrusting Indian lithosphere on the Tibetan subcontinental lithospheric mantle in space and time than previously thought.