Abstract
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 (δ66Zn) in subducted Alpine serpentinites to decipher the chemical properties of slab-derived fluids. We show that the progressive decrease in δ66Zn with metamorphic grade is correlated with a decrease in sulfur content. As existing theoretical work predicts that Zn-SO42− complexes preferentially incorporate heavy δ66Zn, our results provide strong evidence for the release of oxidized, sulfate-rich, slab serpentinite-derived fluids to the mantle wedge.
Highlights
Subduction zones modulate the chemical evolution of the Earth’s mantle
Arc lavas erupted at convergent plate boundaries have geochemical signatures that differ from other mantlederived magmas. They are considered to be more oxidized than mid-ocean-ridge basalts[1,2,3,4,5] and are enriched in fluid-mobile and volatile elements[6], a geochemical signature that reflects the interaction of mantle wedge peridotites with fluids released by the downgoing slab[3,7]
We investigate the nature of slab-derived fluids and trace their transfer to the mantle wedge through a Zn isotope study of Alpine meta-ophiolites and Himalayan ultramafic samples
Summary
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. Arc lavas erupted at convergent plate boundaries have geochemical signatures that differ from other mantlederived magmas They are considered to be more oxidized than mid-ocean-ridge basalts[1,2,3,4,5] and are enriched in fluid-mobile and volatile elements[6], a geochemical signature that reflects the interaction of mantle wedge peridotites with fluids released by the downgoing slab[3,7]. Sample a paleo-slab and record different stages of prograde, subduction-related metamorphism (from green-schist to eclogite facies)[24,25] They are mostly composed of serpentinites[24,25,26] that are formed by the hydration and oxidation of the oceanic lithosphere and can incorporate up to 13% of water[8], as well as sulfur and chalcophile elements mainly as sulfides[15,27]. Debret et al.[29] observed that the Fe isotope compositions of theses with metamorphic grade serpentinites as bulk Fe3 þ
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