Nature of the Mantle Plume Under the Emeishan Large Igneous Province: Constraints From Olivine-Hosted Melt Inclusions of the Lijiang Picrites

Olivine-hosted melt inclusions have the potential to provide direct evidence about the nature of the mantle sources of magmas. In this study, we report the major and trace element and Sr-Nd-Pb-Hf isotope compositions of the Lijiang picrites from the Emeishan large igneous province, as well as major and trace element and Pb isotopic compositions of olivine-hosted melt inclusions in the picrites. Using these data, we infer the nature of the mantle sources for the Lijiang high-Ti picrites (Ti/Y = 645-654), and compare them with the Dali low-Ti picrites (Ti/Y = 351-408). Lijiang melt inclusions have highly heterogeneous Pb isotope compositions (Pb-208/Pb-206 = 2.015-2.201, Pb-207/Pb-206 = 0.812-0.882, 260 Ma age-corrected) that overlap the majority of the fields from FOZO to enriched mantle 1 (EM1). The primitive mantle-normalized trace element patterns of these melt inclusions reveal an enriched composition with depletions in Ba, Nb, Ta, Zr, and Hf. We suggest that an old recycled GLOSS II-like sediment was probably the main component that imparted the EM1 signature into the sources of the Lijiang picrites. Furthermore, we reverse calculated the mantle potential temperature (T-p) beneath Lijiang and Dali using the Al-in-ol temperature. The estimated mantle T-p beneath Lijiang is lower than Dali. We infer that the Lijiang picrites might have originated from the mantle plume with lower thermal energy, corresponding to the waning stage of the axis of the Emeishan mantle plume. Our study suggest that high-Ti magmas of the Emeishan large igneous province were derived from those parts or stages of the mantle plume with lower thermal energy.