Maffeis Andrea, Frezzotti Maria Luce, Connolly James Alexander Denis, Castelli Daniele, Ferrando Simona
Università di Torino, Dipartimento di Scienze della Terra, Torino, Italy.
Università degli Studi di Milano-Bicocca, Dipartimento di Scienze dell'Ambiente e della Terra, Milano, Italy.
Sci Adv. 2024 Mar 22;10(12):eadj2770. doi: 10.1126/sciadv.adj2770. Epub 2024 Mar 20.
Sulfur degassed at volcanic arcs calls for dissolved sulfate ions (S) 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 , 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.
火山弧处脱气的硫需要俯冲带流体释放的溶解硫酸根离子（S），使弧下地幔氧化（与碳相关联），但弧下深度俯冲流体中的硫形态仍不清楚。我们应用电解液热力学来模拟黄铁矿在变质碳酸盐沉积物中的溶解行为，该行为是压力、温度和岩石氧化还原状态的函数，压力可达4.3吉帕斯卡，温度可达730°C。在弧下深度以及铁橄榄石-磁铁矿-石英氧缓冲剂的氧化还原条件下，黄铁矿溶解通过歧化作用向流体中释放出氧化态的硫，生成硫酸根、亚硫酸氢根和硫化物物种。这些发现表明，在深度大于100千米的俯冲板块内会形成氧化态的、富含硫的碳-氧-氢-硫（COHS）流体，其形成与板块的氧化还原状态无关，并且在氧化地幔楔方面，硫可能比同时溶解的碳更有效，尤其是当碳酸盐稳定时。
