The Comoros archipelago is an active geodynamic region of intra-plate volcanism within which the youngest and oldest islands (Grande Comore and Mayotte respectively) are characterized by recent volcanic activity. The frequent eruptions of the large shield volcano Karthala on Grande Comore (last eruption 2007), and the recent birth of a large submarine volcano since 2018 at the submarine base of Mayotte are associated with permanent fumarolic emissions, bubbling gas seeps, and soil gas emissions, which are studied in detail here for the first time. CO₂ fluxes and chemical and isotopic gas compositions acquired during two surveys in 2017 and 2020 are integrated with older data sets collected between 2005 and 2016, permitting the identification of a possible influence of the recent volcanic and magmatic activity at Mayotte. At Karthala, high gas fluxes with high temperature, and a marked magmatic signature are concentrated close to the summit crater area, while only weaker emissions with a stronger biogenic signature are found on the volcano flanks. At Mayotte, lower temperature and higher CH₄ content are recorded in two main seep areas of CO₂-rich fluid bubbling, while soil emissions on land record a higher proportion of magmatic fluids compared to Karthala. Our preliminary results reveal two quite separate gas emission patterns for each island that are distinct in composition and isotopic signatures, and well correlated with the present state of volcanic activity. This work may potentially provide support for local observation infrastructures and contribute to the improvement in volcanic and environmental monitoring.

中文翻译：

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印度洋格兰德科摩罗和马约特火山群岛（科摩罗群岛）的气体地球化学

科摩罗群岛是一个活跃的板块内火山活动地球动力学区域，其中最年轻和最古老的岛屿（分别是大科摩罗和马约特岛）以最近的火山活动为特征。Grande Comore 上的大型盾构火山 Karthala 频繁喷发（上次喷发于 2007 年），以及最近自 2018 年以来在马约特岛潜艇基地诞生的大型海底火山都与永久性喷气式排放、冒泡气体渗漏和土壤气体排放有关，这里是第一次详细研究。CO ₂2017 年和 2020 年两次调查期间获得的通量以及化学和同位素气体成分与 2005 年至 2016 年期间收集的旧数据集相结合，从而可以确定马约特岛最近的火山和岩浆活动可能产生的影响。在 Karthala，高温的高气体通量和明显的岩浆特征集中在山顶火山口区域附近，而在火山侧翼仅发现具有更强生物特征的较弱排放物。在马约特岛，在 CO _{2 的}两个主要渗漏区域中记录到较低的温度和较高的 CH ₄含量-丰富的流体冒泡，而与卡塔拉相比，陆地上的土壤排放记录了更高比例的岩浆流体。我们的初步结果揭示了每个岛屿的两种完全不同的气体排放模式，它们的成分和同位素特征不同，并且与火山活动的当前状态密切相关。这项工作可能会为当地观测基础设施提供支持，并有助于改进火山和环境监测。