Progressive sub-arc mantle oxidation modulated by sediment melt

The redox state of the sub-arc mantle beneath volcanic arcs is typically oxidized but exhibits substantial variability. Previous studies proposed that the incorporation of slab components alters both arc magma compositions and sub-arc mantle redox state, whereas the dominant component remains debated. Here, by compiling global Cenozoic primitive arc basalt and olivine-hosted melt inclusion data, we show that sediment melt dominated by terrigenous origin plays the controlling role. Progressive influx of sediment melts into the sub-arc mantle results in gradual enrichment of potassium oxide and most incompatible elements in arc magmas. Increases in potassium oxide content in primitive magmas also correlates with rising oxygen fugacity (fo₂) values, highlighting the strong oxidizing potential of sediment melt. The high-potassium oxide, high-fo₂ arc magmas spatially correlate with the distribution of Cenozoic porphyry copper-gold deposits, showing that the sediment melt influx not only elevates the sub-arc mantle fo₂ but also enhances the metallogenetic potential for porphyry deposits.