Supplementary Tables S1-S7

High-pressure experiments reveal that sulfate-rich sediments have a solidus temperature approximately 50 °C lower than graphite-rich sediments at 1–3 GPa, making them prone to partial melting under typical subduction zone conditions while reduced sediments remain stable even in hot slabs. This contrast implies that sulfate-rich sediments are preferentially recycled into arc magmas, whereas graphite-rich sediments are more likely to be transported into the deep mantle. Simulations further indicate that sediment melts have a negligible oxidizing effect on the mantle wedge, and that deeply subducted reduced sediments contribute to forming mantle reservoirs with radiogenic Pb–Os isotopic compositions.