Volcanism of the Comoros archipelago and structural inheritance of the Somali basin, in the Mozambique channel, Indian Ocean.

The Mayotte volcanic island, located in the Comoros archipelago between Madagascar and Mozambique, went through a significant seismic-volcanic crisis in 2018, linked to the construction of a new underwater volcanic structure, Fani Maoré. We used marine geophysical data (seismic reflection, OBS) acquired during an oceanographic cruise in 2020-2021 to explore the architecture of sedimentary, volcanic, and crustal domains within the basin. The study unveils the internal structure of the Fani Maoré volcano and establishes the onset of Mayotte Island's construction between 26 and 28 million years ago, modifying earlier dating assessments. Additionally, we identified volcanic construction phases of the Comoros archipelago's islands between the early Oligocene to the Quaternary, exhibiting similarities with the volcanic evolution of Madagascar and the East African Rift System. Finally, crustal domain analysis suggests that the crust around the Comoros is oceanic, and the opening direction of the Somali basin, with the presence of ancient fracture zones, played a role in the archipelago's formation.