Department of Earth Sciences, Cambridge University, Downing St, Cambridge CB2 3EQ, UK.
Department of Earth Sciences, Durham University, Elvet Hill, Durham DH1 3LE, UK.
Nat Commun. 2016 Dec 16;7:13794. doi: 10.1038/ncomms13794.
Subduction zones modulate the chemical evolution of the Earth's mantle. Water and volatile elements in the slab are released as fluids into the mantle wedge and this process is widely considered to result in the oxidation of the sub-arc mantle. However, the chemical composition and speciation of these fluids, which is critical for the mobility of economically important elements, remain poorly constrained. Sulfur has the potential to act both as oxidizing agent and transport medium. Here we use zinc stable isotopes (δZn) in subducted Alpine serpentinites to decipher the chemical properties of slab-derived fluids. We show that the progressive decrease in δZn with metamorphic grade is correlated with a decrease in sulfur content. As existing theoretical work predicts that Zn-SO complexes preferentially incorporate heavy δZn, our results provide strong evidence for the release of oxidized, sulfate-rich, slab serpentinite-derived fluids to the mantle wedge.
俯冲带调节了地球地幔的化学演化。板块中的水和挥发性元素以流体的形式释放到地幔楔中，这一过程被广泛认为导致了亚弧地幔的氧化。然而，对于经济上重要元素的迁移性至关重要的这些流体的化学组成和形态仍未得到很好的限制。硫具有作为氧化剂和运输介质的双重作用。在这里，我们使用俯冲的阿尔卑斯蛇纹岩中的锌稳定同位素 (δZn) 来破译源自板块的流体的化学性质。我们表明，δZn 随变质程度的逐渐降低与硫含量的降低相关。由于现有理论工作预测 Zn-SO 配合物优先吸收重 δZn，因此我们的结果为释放氧化的、富含硫酸盐的、源自板块蛇纹岩的流体到地幔楔提供了有力证据。
