资源环境科技发展态势分析平台

Sulfur belongs among H2O, CO2, and Cl as one of the key volatiles in Earth's chemical cycles. High oxygen fugacity, sulfur concentration, and delta S-34 values in volcanic arc rocks have been attributed to significant sulfate addition by slab fluids. However, sulfur speciation, flux, and isotope composition in slab-dehydrated fluids remain unclear. Here, we use high-pressure rocks and enclosed veins to provide direct constraints on subduction zone sulfur recycling for a typical oceanic lithosphere. Textural and thermodynamic evidence indicates the predominance of reduced sulfur species in slab fluids; those derived from metasediments, altered oceanic crust, and serpentinite have delta S-34 values of approximately -8, -1 parts per thousand, and+8 parts per thousand, respectively. Mass-balance calculations demonstrate that 6.4% (up to 20% maximum) of total subducted sulfur is released between 30-230km depth, and the predominant sulfur loss takes place at 70-100km with a net delta S-34 composition of -2.5 +/- 3 parts per thousand. We conclude that modest slab-to-wedge sulfur transport occurs, but that slab-derived fluids provide negligible sulfate to oxidize the sub-arc mantle and cannot deliver S-34-enriched sulfur to produce the positive delta S-34 signature in arc settings. Most sulfur has negative delta S-34 and is subducted into the deep mantle, which could cause a long-term increase in the delta S-34 of Earth surface reservoirs.