Olivines and Their Melt Inclusions in Potassic Volcanic Rocks Record Mantle Heterogeneity beneath the Southern Tibet

Abstract Constraints on mantle heterogeneity are important for understanding geochemical differentiation and recycling in Earth’s interior. Alkali basalts of particular interest this context due to the clear signatures recycled components that they yield. Previous studies have focused more oceanic than continental mafic rocks because chemical isotopic characteristics latter often modified by crustal contamination; however, high-forsterite olivine crystals olivine-hosted melt inclusions may record compositions primitive melts before extensive contamination, providing valuable insights into heterogeneity. Here we report results high-precision major-, minor-, trace-element Pb isotope analyses phenocrysts from Sailipu potassic alkali southern Tibet, which constrain source basalts. The minor- (e.g. Ni Ca contents 100 × Mn/Fe, 10 000 Zn/Fe, Ni/Co ratios) suggest primary magmas were derived a phlogopite-bearing pyroxenite peridotite residues also present. low- high-Li material their source. Comparing major-element SiO2, TiO2, Al2O3, MnO, CaO, Na2O contents), FCMS FCKANTMS parameters, pseudo-ternary projections with experimental data suggests partial olivine-poor or carbonated lithologies small amount residue. negative Nb Ta positive anomalies seen mantle-normalized patterns extremely low Nb/U ratios crust was main process involved enriching magmas. heterogeneous (208Pb/206Pb = 2.089 – 2.158; 207Pb/206Pb 0.851 0.858) consistent presence residue subduction Indian introduced enriched (including carbonatites) mantle.