Identifying mantle carbonatite metasomatism through Os–Sr–Mg isotopes in Tibetan ultrapotassic rocks.

摘要: Mantle-derived magmas at convergent plate boundaries provide unique insights into the nature of materials subducted to and recycled from depths. Here we present a study Os–Sr–Mg isotopes on Oligocene–Miocene ultrapotassic rocks aimed better understanding sediment subduction recycling beneath southern Tibet. New isotopic data confirm that in Tibet are mantle origin, but underwent crustal contamination as evidenced by variably high 187Os/188Os obviously deviates normal reservoir. Still some samples with mantle-like exhibit δ26Mg significantly lower than lithologies, suggesting isotopically light Mg may not result retain specific fingerprint carbonate-related metasomatism sources. Mantle carbonatite is manifested inverse δ26Mg–87Sr/86Sr correlations, well depletion field strength elements relative rare earth enrichment CaO rocks. The positive co-variations between Hf/Sm defined those low-187Os/188Os evidence for potential dolomites modify composition. correlated spatial variations interpreted reflect carbonatitic associated northward Neo-Tethyan oceanic slab its profound influence postcollisional magmatism.