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

俯冲带是地球外圈和地幔之间大规模二氧化碳循环的构造环境，这对建立和维持一个适宜居住的星球具有关键影响。来自大气和水圈的大量碳储存在沉积物和海洋岩石圈中，可以通过俯冲返回地幔，并通过弧火山作用部分循环回到地表。由于缺乏关于母体熔体中二氧化碳丰度的准确数据，到目前为止，弧火山作用产生的二氧化碳的程度和效率仍然很难受到限制，现有的模型大多依赖于高温火山气体数据。德国-俄罗斯的这一双边研究项目旨在提供有关俯冲带二氧化碳循环的基本信息和目前缺失的信息，重点是准确确定千岛-堪察加、中美洲和卡拉布里亚三个活跃火山弧--代表全球火山气体中二氧化碳/S比率的整个范围--母岩浆中二氧化碳的初始浓度。我们的目标将通过分析橄榄石熔体包裹体中的挥发性含量来实现。为了消除对熔体包裹体的捕获后修改，它们将通过加热和重新水化完全均化，使用最先进的单气氛和高压实验，为直接分析测定熔体包裹体中的大量二氧化碳含量提供了可能性。这些数据将被用来量化二氧化碳在具有代表性的弧状岩浆中的转移，这些岩浆在源区具有不同的碳化物质贡献。所获得的结果将是检验火山气体化学与岩浆熔体成分之间的直接联系的关键。此外，它们将有助于确定岩浆中二氧化碳浓度的潜在痕量元素和同位素替代物，使我们能够通过使用其他地球化学参数来估计俯冲时的二氧化碳输入和输出通量。

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.