Deciphering the origin and emplacement mechanisms of Mayotte submarine and subaerial volcaniclastic deposits using x-ray tomography and geochemical fingerprinting

In 2021, 25 sediment cores were gathered in the proximal region of Mayotte Island, in the Comoros Archipelago. A total of ~300 meters was retrieved shedding light into the past volcanic activity of the island, but also of the submarine Eastern Mayotte Volcanic Chain (EMVC) discovered in 2019. By investigating the sediment cores, up to 1 cm resolution scale in the uppermost sedimentary sequence of core MAY15-CS02, we underlined the presence of abundant, fresh, cryptotephra witnessing recent explosive activity from ~2 to 6.5 ka, and a major event at 7.5 ka that could either originate from Petite-Terre or the submarine Horseshoe volcano ^[1]. We also identified new submarine explosive eruptions of phonolitic composition, marked by high-alkali contents, which differs from the most recent activity of Petite-Terre and the Horseshoe ^[2]. A 1-meter-thick deposit dated at around 300 ka presents a less evolved composition than the aforementioned eruptions, and coarser material up to several centimetres scale composed this deposit, shedding light on another major volcanic event that affected Mayotte. Using high-resolution x-ray tomography 3D scans and geochemical analyses together with textural observations, we investigate its origin (subaerial vs. submarine) and emplacement mechanisms, and fine tune Mayotte volcanic history. We present here the key results of this investigation and emphasize the importance of analysing, at a high resolution, proximal (≤5 km from the island coast) sediment cores as they do contain crucial information retrieved from volcanic-related deposits, tephra and cryptotephra to comprehend the overall activity that shaped an island.

^[1] Lebas et al. 2024. IAVCEI-COT abstract, Catania.
^[2] Baudry et al. 2025. IAVCEI abstract, Geneva.