Iron oxidation state in the hydrated cold mantle wedge

Earth's interior has absorbed excess oxygen through subduction of oxidized plates. A potential storage site for oxidized species, often overlooked, is the mantle wedge above subducting slabs. Hydration of mantle rocks at the sea floor increases magnetite content and Fe3+/Fetotal ratios, but this process is less understood at high pressures in the mantle wedge. Preliminary data from rare mantle wedge samples show low magnetite content despite high hydration. We propose to measure Fe3+/Fetotal ratios in hydrous phases to understand the cold, hydrated mantle wedge as a storage site for oxidized species. We will analyze Fe3+/Fetotal in ferromagnesian minerals across several hydration stages using micro-synchrotron Mössbauer source spectroscopy at ID14, ESRF. We aim to determine whether the cold, hydrous mantle wedge serves as a significant ferric iron reservoir, impacting our understanding of oxidized species recycling in subduction zones.