Release of oxidizing fluids in subduction zones recorded by iron isotope zonation in garnet

Gerrits, Anna R.; Inglis, Edward; Dragovic, Besim; Starr, Paul G.; Baxter, Ethan F.; Burton, Kevin

Abstract

Subduction zones are key regions of chemical and mass transfer between the Earth’s surface and mantle. During subduction, oxidized material is carried into the mantle and large amounts of water are released due to the breakdown of hydrous minerals such as lawsonite. Dehydration accompanied by the release of oxidizing species may play a key role in controlling redox changes in the subducting slab and overlying mantle wedge. Here we present measurements of oxygen fugacity, using garnet–epidote oxybarometry, together with analyses of the stable iron isotope composition of zoned garnets from Sifnos, Greece. We find that the garnet interiors grew under relatively oxidized conditions whereas garnet rims record more reduced conditions. Garnet δ56Fe increases from core to rim as the system becomes more reduced. Thermodynamic analysis shows that this change from relatively oxidized to more reduced conditions occurred during lawsonite dehydration. We conclude that the garnets maintain a record of progressive dehydration and that the residual mineral assemblages within the slab became more reduced during progressive subduction-zone dehydration. This is consistent with the hypothesis that lawsonite dehydration accompanied by the release of oxidizing species, such as sulfate, plays an important and measurable role in the global redox budget and contributes to sub-arc mantle oxidation in subduction zones.

Citation

Gerrits, A. R., Inglis, E., Dragovic, B., Starr, P. G., Baxter, E. F., & Burton, K. (2019). Release of oxidizing fluids in subduction zones recorded by iron isotope zonation in garnet. Nature Geoscience, 12, 1029-1033. https://doi.org/10.1038/s41561-019-0471-y

• Journal Article Type: Article
• Acceptance Date: Aug 27, 2019
• Online Publication Date: Oct 28, 2019
• Publication Date: 2019
• Deposit Date: Sep 12, 2019
• Publicly Available Date: Apr 28, 2020
• Journal: Nature Geoscience
• Print ISSN: 1752-0894
• Electronic ISSN: 1752-0908
• Publisher: Nature Research
• Peer Reviewed: Peer Reviewed
• Volume: 12
• Pages: 1029-1033
• DOI: https://doi.org/10.1038/s41561-019-0471-y
• Public URL: https://durham-repository.worktribe.com/output/1287281