Birth of a large volcanic edifice through lithosphere-scale dyking offshore Mayotte (Indian Ocean)

We document here an on-going magmatic event, offshore Mayotte Island (North Mozambique channel) that is unprecedented in emitted lava volume and duration. The event is associated with unusually large surface displacements, intense and long-lasting seismic activity and very low frequency earthquakes. Data from the May 2019 SISMAYOTTE/MAYOBS1 cruise (doi.org/10.17600/18001217) reveal that this event gave birth to a 820m tall, ~ 5 km3 deep-sea volcanic edifice, whose summit emanated a 1900 m -high acoustic plume with a strong chemical signature. The new volcanic edifice is located at the tip of a volcanic ridge (Mayotte ridge) composed of many recent edifices and lava flows, which extends offshore from Mayotte's Petit-Terre island. Earthquakes, located from a local land and seafloor seismology network, are exceptionally deep (25-50 km) below the ridge. Their spatio-temporal distribution indicates the rapid drainage of a deep magma reservoir (~ 50 km) through dykes that intruded the entire lithosphere and the possible reactivation of pre-existing subvertical faults in the mantle beneath an ancient caldera structure. The Mayotte ridge was built as a result of multiple eruptions along an extensional tectonic structure that opens to transfer the strain between the East-African and Madagascar rifts. This structure cuts across the entire lithosphere and serves as a pathway for deeply ponded magma. The exceptional volumes and flow rates likely result from the interaction between a hot asthenosphere and extensional tectonics. As of July 2020, the seismic activity and deformation are still ongoing. Since the discovery of the NVE, several new lava flows and acoustic plumes have been observed in 2019 and 2020 during five oceanographic cruises of the MAYOBS (doi.org/10.18142/291)/REVOSIMA monitoring program.