Carbonate- and silicate-metasomatized mantle beneath Himalayan-Tibetan orogenic belt.

The extreme geochemical enrichment of post-collisional potassium-rich lava in the Alpine-Himalayan orogenic belt has led researchers to hypothesize that enrichment is inherited from a metasomatized mantle source potentially incorporating crustal components. However, direct verification of metasomatic processes remains challenging due to the scarcity of mantle rocks preserving metasomatism records. Here, we report two groups of mantle xenolith entrained in Tibetan ultrapotassic lavas. Integrated petrographic observations, whole-rock geochemistry, and in-situ microanalysis reveal that subcontinental lithospheric mantle exhibits extreme enrichment in both isotopes and incompatible elements. Textural evidence of vein networks and melt pockets in xenoliths indicate the coexistence of carbonate and silicate metasomatic regimes. Considering subduction-collision background, we propose that the recycling of Indian continental materials during collision substantially contributes to the metasomatic enrichment of the Tibetan subcontinental lithospheric mantle.