Sulfur degassed at volcanic arcs calls for dissolved sulfate ions (S6+) released by subduction-zone fluids, oxidizing (in association with carbon) the subarc mantle, but sulfur speciation in subduction fluids at subarc depths remains unclear. We apply electrolytic fluid thermodynamics to model the dissolution behavior of pyrite in metacarbonate sediments as a function of P, T and rock redox state up to 4.3 gigapascals and 730°C. At subarc depth and the redox conditions of the fayalite-magnetite-quartz oxygen buffer, pyrite dissolution releases oxidized sulfur in fluids by disproportionation into sulfate, bisulfite, and sulfide species. These findings indicate that oxidized, sulfur-rich carbon-oxygen-hydrogen-sulfur (COHS) fluids form within subducting slabs at depths greater than 100 kilometers independent from slab redox state and that sulfur can be more effective than the concomitantly dissolved carbon at oxidizing the mantle wedge, especially when carbonates are stable.

Maffeis, A., Frezzotti, M., Connolly, J., Castelli, D., Ferrando, S. (2024). Sulfur disproportionation in deep COHS slab fluids drives mantle wedge oxidation. SCIENCE ADVANCES, 10(12) [10.1126/sciadv.adj2770].

Sulfur disproportionation in deep COHS slab fluids drives mantle wedge oxidation

Maffeis, A
;
Frezzotti, ML
;
2024

Abstract

Sulfur degassed at volcanic arcs calls for dissolved sulfate ions (S6+) released by subduction-zone fluids, oxidizing (in association with carbon) the subarc mantle, but sulfur speciation in subduction fluids at subarc depths remains unclear. We apply electrolytic fluid thermodynamics to model the dissolution behavior of pyrite in metacarbonate sediments as a function of P, T and rock redox state up to 4.3 gigapascals and 730°C. At subarc depth and the redox conditions of the fayalite-magnetite-quartz oxygen buffer, pyrite dissolution releases oxidized sulfur in fluids by disproportionation into sulfate, bisulfite, and sulfide species. These findings indicate that oxidized, sulfur-rich carbon-oxygen-hydrogen-sulfur (COHS) fluids form within subducting slabs at depths greater than 100 kilometers independent from slab redox state and that sulfur can be more effective than the concomitantly dissolved carbon at oxidizing the mantle wedge, especially when carbonates are stable.
Articolo in rivista - Articolo scientifico
Sulfur, carbon, Subduction, Wedge oxidation
English
20-mar-2024
2024
10
12
eadj2770
open
Maffeis, A., Frezzotti, M., Connolly, J., Castelli, D., Ferrando, S. (2024). Sulfur disproportionation in deep COHS slab fluids drives mantle wedge oxidation. SCIENCE ADVANCES, 10(12) [10.1126/sciadv.adj2770].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/474987
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