Mantle wedge oxidation due to sediment-infiltrated deserpentinisation Padrón Navarta, José Alberto Sánchez-Vizcaíno, Vicente López Menzel, Manuel Dominik Gómez Pugnaire, María Teresa Garrido Marín, Carlos J. This work is part of the project DESTINE (PID2019-105192GB-I00) funded by MICIN/AEI/10.13039/501100011033 and the FEDER program “una manera de hacer Europa”. J.A.P.N. acknowledges a Ramón y Cajal contract (RYC2018-024363-I) funded by MICIN/AEI/10.13039/501100011033 and the FSE program “FSE invierte en tu futuro”. This research is part of the Junta de Andalucia research group RNM-131. The Earth's mantle is oxygen-breathing through the sink of oxidised tectonic plates at convergent Margins. Ocean floor serpentinisation increases the bulk oxidation state of iron relative to dry oceanic mantle and results in a variable intake of other redox-sensitive elements such as sulphur. The reversibility of seafloor oxidation in subduction zones during high-pressure dehydration of serpentinite (“deserpentinisation”) at subarc depths and the capacity of the resulting fluids to oxidise the mantle source of arc basalts are highly contested. Thermodynamic modelling, experiments, and metaperidotite study in exhumed highpressure terrains result in differing estimates of the redox state of deserpentinisation fluids, ranging from low to highly oxidant. Here we show that although intrinsic deserpentinisation fluids are highly oxidant, the infiltration of small fractions of external fluids equilibrated with metasedimentary rocks strongly modulates their redox state and oxidation-reduction capacity explaining the observed discrepancies in their redox state. Infiltration of fluids equilibrated with graphite-bearing sediments reduces the oxidant, intrinsic deserpentinisation fluids to oxygen fugacities similar to those observed in most graphite-furnace experiments and natural metaperidotites. However, infiltration of CO2-bearing fluids equilibrated with modern GLOSS generates sulphate-rich, highly oxidising deserpentinisation fluids. We show that such GLOSS infiltrated deserpentinisation fluids can effectively oxidise the mantle wedge of cold to hot subduction zones potentially accounting for the presumed oxidised nature of the source of arc basalts. 2023-05-17T11:13:47Z 2023-05-17T11:13:47Z 2023 journal article Published version: Padrón-Navarta, J.A., López Sánchez-Vizcaíno, V., Menzel, M.D. et al. Mantle wedge oxidation from deserpentinization modulated by sediment-derived fluids. Nat. Geosci. 16, 268–275 (2023). [https://doi.org/10.1038/s41561-023-01127-0] https://hdl.handle.net/10481/81618 10.1038/s41561-023-01127-0 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Springer Nature