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 ( f o 2 ) values, highlighting the strong oxidizing potential of sediment melt. The high–potassium oxide, high- f o 2 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 f o 2 but also enhances the metallogenetic potential for porphyry deposits.