Carbon recycling by arc magmatism: an assessment from experimentally homogenized melt inclusions in olivine

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Subduction zones are tectonic setting of a large-scale CO2 recycling between the exosphere and the mantle on Earth that has a key influence on building and sustaining a habitable planet. A large amount of carbon from atmosphere and hydrosphere, stored in sediments and oceanic lithosphere, can be returned to the mantle via subduction and partly recycled back to the surface by arc volcanism. The extent and the efficiency of CO2 output by arc volcanism remains poorly constrained to date due to the scarcity of accurate data on CO2 abundance in parental arc melts, and the available models mostly rely on high-temperature volcanic gas data. This bilateral German-Russian research project aims at providing fundamental and currently missing information on the CO2 cycle at subduction zones and focuses on the accurate determination of the initial concentration of CO2 in parental magmas from 3 active volcanic arcs: – Kuril-Kamchatka, Central American and Calabrian arcs – representing the entire range of CO2/S ratios in volcanic gases globally. Our goal will be achieved by analyzing the volatile contents in melt inclusions in olivine. To eliminate post-entrapment modifications of melt inclusions, they will be completely homogenized by heating and re-hydration using state-of-the-art one-atmosphere and high-pressure experiments, providing the possibility for direct analytical determination of bulk CO2 content in melt inclusions. The data will be used to quantify the transfer of CO2 in representative arc magmas with various contribution of carbonated material in the source. The obtained results will be crucial to test the proposed direct link of the volcanic gas chemistry with the composition of magmatic melts. Furthermore, they will help to identify potential trace element and isotope proxies for CO2 concentrations in magmas, allowing us to estimate input and output CO2 fluxes at subduction by using other geochemical parameters.