Uncovering and quantifying the subduction zone sulfur cycle from the slab perspective
Uncovering and quantifying the subduction zone sulfur cycle from the slab perspective
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从板块角度揭示和量化俯冲带硫循环
DOI：
10.1038/s41467-019-14110-4
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发表时间：
2020-01-24
影响因子：
16.6
通讯作者：
Wang, Xin-Shui
中科院分区：
文献类型：
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作者：
Li, Ji-Lei;Schwarzenbach, Esther M.;Wang, Xin-Shui
硫是地球化学循环中的关键挥发物之一，属于H2O、CO2和Cl。火山岩的高氧逸度、高硫浓度和高S-34值是由于板状流体对硫酸盐的大量添加。然而，板状脱水流体中硫的形态、通量和同位素组成仍不清楚。本文利用高压岩石和封闭脉体对典型海洋岩石圈俯冲带硫循环进行了直接约束。构造和热力学证据表明，板状流体中硫化物以还原态为主；源自变质沉积物、蚀变海洋地壳和蛇纹岩的δ S-34值分别约为-8、-1和+8。质量平衡计算表明，总俯冲硫的6.4%（最大可达20%）在30-230公里深度之间释放，主要的硫损失发生在70-100公里处，净δ S-34组成为-2.5 +/- 3‰。我们得出的结论是，存在适度的板状到楔状硫输运，但板状衍生流体提供的硫酸盐可以忽略，无法氧化弧下地幔，无法输送S-34富集硫，从而在弧环境中产生正的δ S-34特征。大多数硫具有负S-34 δ，并俯冲到深部地幔，这可能导致地表储层S-34 δ长期增加。
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.