V020-0028
Mantle xenoliths-bearing phonolites feeding the active volcanic ridge of Mayotte (Comoros archipelago, Mozambique Channel)
Thursday, 10 December 2020
Poster
Carole Berthod1, Théo Hassen Ali1, Etienne Médard1, Andrea Di Muro2, Lucia Gurioli1, Patrick Bachelery1, Didier Laporte1, Aline Peltier3, Jean-Christophe Komorowski4, Mhammed Benbakkar1, Jean-Luc Devidal1, Jessica Langlade5, Pascale Besson4, Georges Boudon4, Estelle F Rose-Koga1, Christine Deplus6, Anne Le Friant7, Manon Bickert4, Sophie Nowak8, Isabelle Thinon9, Pierre Burckel4, Samia Hidalgo4, Stephan Jorry10, Yves Fouquet10 and Nathalie Feuillet4, (1)Université Clermont Auvergne, CNRS, IRD, OPGC, Laboratoire Magmas et Volcans, Aubiere, France, (2)Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, Observatoire Volcanologique du Piton de la Fournaise, Bourg Murat, France, (3)Université de Paris, Institut de Physique du Globe de Paris (IPGP), UMR 7154, Paris, France, (4)Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, Paris, France, (5)IUEM Institut Universitaire Européen de la Mer, Plouzané, France, (6)IPGP & CNRS, Paris Cedex 05, France, (7)Université de Paris,, Institut de physique du globe de Paris, CNRS,, Paris, France, (8)Sorbonne Paris Cité, Université Paris Diderot, Paris, France, (9)BRGM - French geological survey, Orléans, France, (10)IFREMER, Plouzané, France
Abstract:
The Comoros volcanic archipelago is related to a complex E-W zone of immature right-lateral wrenching of the lithosphere in the context of the Lwandle and Somalian plate boundaries. A major volcano-tectonic crisis began in May 2018 offshore Mayotte resulting in the construction of a large (at least 6.4 km
3 bulk as of May 2020) submarine volcanic edifice 50 km east of the island. The eruptive site is located on the distal part of a 60 km long NW-SE volcanic ridge that runs off the eastern flank of Mayotte and whose subaerial expression is Petite Terre Island. The presence of Holocene phonolitic maars, resulting from explosive dynamism, identified in the east of Petite Terre Island, raises the question of possible future volcanic activity on land.
We will present a petrological study of samples collected on Petite Terre Island and through dredges about 10 km offshore on the volcanic ridge to image and understand the magmatic system. Our petrological analyses reveal that identical bimodal magmatism characterizes the volcanic ridge and Petite Terre Island, ranging from basanites (3.14 - 5.67 wt.% MgO) to phonolites (0 - 0.5 wt.% MgO). A geobarometric study of the basanites from the ongoing eruption using clinopyroxene phenocrysts indicates multiple levels of magma storage starting with a deep mantle reservoir > 30 km depth and a shallower reservoir located near the Moho around 20 km depth. Volcanism on land and offshore are thus sustained by an identical plumbing system and are strongly linked.
The phonolitic magmas feeding both the active NW-SE volcanic ridge of Mayotte and the Holocene volcanism of Petite Terre are exceptional because they contain mantle xenoliths, indicating that strongly differentiated magmas were produced and stored in a mantle reservoir. Using two pyroxenes geobarometry on the xenoliths, we will show that this reservoir is located just below the mantle/crust boundary. The fact that differentiation processes operate in the mantle promoting the genesis of volatile-rich magmas, and the absence of shallow reservoirs has strong implications for the dynamics of rapid magma ascent, the possibility of detecting precursory signals and for associated volcanic hazards, should the ongoing offshore volcanic activity migrates towards land or reactivates existing storage zones of eruptible magma.
