Marine Manoux defended her thesis on 17 December 2024 at the LSCE. Her work focuses on the influence of the Fani Maoré submarine volcano (Mayotte) on sedimentary deposits and early diagenesis, based on the study of elemental and isotopic tracers (Fe, C, Sr). This research, funded by IFREMER, was co-supervised by Christophe Rabouille (OCEANIS – LSCE), Olivier Rouxel (CYBER – Geo-ocean) and Cécile Cathalot (CYBER – Geo-ocean). The defence jury was composed of Pierre Anschutz, university professor at EPOC, and Vincent Busigny, university professor at IPGP, as rapporteurs. Géraldine Sarthou, research director at the CNRS, LEMAR, chaired the jury. Cécile Guieu, research director at the CNRS, LOV, and Sune Nielsen, research director at the CNRS, CRPG, participated as examiners. All the samples analysed in this project were sampled during the GEOFLAMME cruise in May 2021 on board the Pourquoi Pas?.
This thesis focuses on the impact of submarine volcanic eruptions on sedimentary processes and early diagenesis, based on the example of the Fani Maoré submarine volcano, which emerged in 2018 near Mayotte. The study is notable for two main aspects: the analysis of the impacts just two years after the eruption, a time scale that is rare in geology, and the geochemical exploration of the sediments in a region that has been poorly studied until now. Geochemical analyses coupled with isotopic analyses of iron, carbon and strontium were essential in identifying the interaction between deep magmatic fluids and surface sediments in an area close to the volcano and lava flows. These tools also made it possible to observe, for the first time in this context, iron-rich carbonates were found in a hydrothermal plume, resulting from fluids enriched in CO2. These carbonates are associated with massive deposits of iron oxyhydroxides at the surface of sediments on a regional scale. The long-term fate of these deposits is dominated by the reduction of iron oxyhydroxides, with dissolution of volcanic material playing a minor role. These discoveries make a valuable contribution to our understanding of the diagenetic and biogeochemical processes induced by submarine eruptions, while opening up new perspectives for the analysis of past eruptions.
