Mantle Source of the High-Ti Magma in the Emeishan Large Igneous Province Is Oxidized

Abstract Oxygen fugacity (ƒO₂) of mantle is a fundamental parameter governing mantle melting, magmatic evolution, and volatile behavior, playing a critical role in material recycling, climate change, and mineralization. This study investigates the redox state of the high-Ti picritic magma in the Emeishan Large Igneous Province (ELIP) by estimating ƒO₂ via the olivine–melt vanadium partition and platinum-group element (PGE) abundances. Olivine compositions and trace element systematics indicate that the primary magmas of high-Ti picrites could be produced through ~5% partial melting from peridotite mantle source at 3.1–5.1 GPa. Olivine–melt V oxybarometry reveals that the primary magmas exhibit relatively high ƒO₂ (ΔFMQ +1.2 to +1.5). The high PGE concentrations (16.0–27.5 ng/g) of the picrites imply that the mantle sulfides were readily dissolved during low-degree partial melting, suggesting that they might have originated from relatively oxidized mantle sources. The elevated ƒO₂, inherent from the mantle source, might have promoted early crystallization of Fe–Ti oxides, which ultimately drives the formation of giant Fe–Ti–V oxide deposits. The PGE depletion in the high-Ti basaltic magmas suggests that sulfide saturation was reached during magma evolution, implying the potential for sulfide-poor PGE mineralization at depth. However, due to the relatively high sulfur contents at sulfide–liquid saturation (SCSS) of these oxidized high-Ti magmas, large-scale Cu–Ni sulfide deposits could form only where sulfur-rich, reducing sedimentary strata were assimilated. Our study offers new insights into how the ƒO₂ of mantle sources influences the metallogeny of large igneous provinces.