Birth of a large volcanic edifice offshore Mayotte via lithosphere-scale dyke intrusion

Abstract

Volcanic eruptions are foundational events that shape the Earth's surface and provide a window into deep Earth processes. How the primary asthenospheric melts form, pond and ascend through the lithosphere is, however, still poorly understood. We document an on-going magmatic event offshore Mayotte Island (North Mozambique channel), associated with large surface displacements, very low frequency earthquakes and exceptionally deep (25-50 km) seismicity swarms. We present data from the May 2019 MAYOBS1 cruise, which reveal that this event gave birth to a 820m tall, ~ 5 km 3 deepsea volcanic edifice. This is the largest active submarine eruption ever documented. The data indicate that deep magma reservoirs were rapidly drained through dykes that intruded the entire lithosphere and that pre-existing subvertical faults in the mantle were reactivated beneath an ancient caldera structure.

Mayotte seismic crisis: building knowledge in near real-time by combining land and ocean-bottom seismometers, first results

“…This proximal cluster appears not connected to the Distal cluster in our dataset and this seems to have been the case since the beginning of the crisis. The Proximal cluster cylindrical shape match existing interpretations of a slowly sagging caldeira piston (Cesca et al, 2020 ;Feuillet et al, 2021), but it could also be an ancient fault zone re-activated by the massive changes in lithosphere constraints due to the eruption. Further detailed interpretation of the Proximal cluster seismic activity requires results from ongoing studies (lithosphere structure studies, high-resolution relocations, source mechanisms).…”

“…The Proximal cluster correlates with seismic activity that initiated during July 2018 (Cesca et al, 2020 ;Lemoine et al, 2020a) and became very active at the end of August 2018. This correspond to the beginning of the island subsidence and eastward displacement as recorded in GNSS data, inferred to be due to the drainage of an at least 30 km deep magma chamber (Briole, 2018 ;Lemoine et al, 2020a ;Cesca et al, 2020 ;Feuillet et al, 2021). This proximal cluster appears not connected to the Distal cluster in our dataset and this seems to have been the case since the beginning of the crisis.…”

“…The seismicity manually-picked and relocated in this study, from February 2019 to May 2020 is in agreement with the analysis of 2018 activity (Cesca et al, 2020;Lemoine et al, 2020a; Table 1), as seismicity clusters identified in this work seems to have been active since summer 2018. The Distal cluster correlates with the first cluster of activity that represents rock fracturing and dyke opening from the center of deflation toward the volcano, leading to the creation of the NVE (Cesca et al, 2020;Lemoine et al, 2020a;Feuillet et al, 2021). However, a noticeable difference with our catalog is the…”

“…On November 11 th 2018, a very low frequency tremor was recorded worldwide (Cesca et al, 2020, Lemoine et al, 2020a, confirming that the seismic crisis was very likely of magmatic origin. This was later confirmed by the discovery of a new submarine volcanic edifice offshore Mayotte during the MAYOBS1 scientific expedition onboard RV Marion Dufresne in May 2019 (Feuillet et al, 2021). This large eruption began either on June 18 th (Cesca et al, 2020) or on July 3 rd 2018 (Lemoine et al, 2020a).…”

“…Because our velocity model was built during the MAYOBS1 cruise, during which we still had intense seismicity with most of the highest magnitude earthquakes of our dataset that occurred in the Proximal cluster (Feuillet et al, 2021), only a few events were located in the Distal cluster. Our velocity model is then mostly constrained by the Proximal events.…”