Pliocene-to-Holocene volcano-tectonic activity on Mohéli Island (Comoros archipelago) constrained by new K Ar ages

• Published in: Journal of Volcanology and Geothermal Research
• Main Authors: Rusquet, Anaïs, Famin, Vincent, Quidelleur, X., Michon, Laurent, Nauret, François, Danišík, Martin, Thinon, Isabelle, Leroy, Sylvie, Lemoine, Anne
• Other Authors: Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Université Paris Cité (UPCité), Laboratoire GéoSciences Réunion (LGSR), Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris), Université Paris-Saclay, Géosciences Paris Saclay (GEOPS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), Laboratoire Magmas et Volcans (LMV), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA), Curtin University, Bureau de Recherches Géologiques et Minières (BRGM), Institut des Sciences de la Terre de Paris (iSTeP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), This research was also funded by the MAYVOLTE grant from the Institut des Sciences de l'Univers (INSU), Centre National de la Recherche Scientifique (CNRS)., ANR-19-CE31-0018,COYOTES,COmores & maYotte : vOlcanisme, TEctonique et Sismicité(2019)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: Comoros archipelago; K-Ar dating; Mohéli Island; Holocene volcanism; Volcano subsidence; Melilitite; Lwandle/Somali plate boundary; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Day Island
• Online Access: https://brgm.hal.science/hal-04191365; https://brgm.hal.science/hal-04191365/document; https://brgm.hal.science/hal-04191365/file/Rusquet_et_al_Moheli_revised_ms_final.pdf; https://doi.org/10.1016/j.jvolgeores.2023.107896

International audience The volcanism of the Comoros archipelago (from west to east: Grande Comore, Mohéli, Anjouan, and Mayotte islands) has been under renewed scientific scrutiny since the eruption of a new submarine volcanic edifice (Fani Maoré) which begun in May 2018 east of Mayotte. West of Mayotte, Mohéli island has received little attention from the geoscience community, despite its largely uneroded volcanic landscapes suggesting a recent activity that has not been dated. Here we address this gap in knowledge by applying Ksingle bondAr geochronology on groundmass and major-trace element analyses to subaerial and submarine rocks, in an attempt to reconstruct the volcano-tectonic and geochemical evolution of Mohéli. Our results show that Mohéli's volcano-tectonic evolution proceeded in two constructional stages, including a primary edification along a N070°E axis from before ca. 3.8 Ma to ca. 3 Ma (Stage 1), and a second construction along a N110°E ridge shaping the present-day island since ca. 2 Ma (Stage 2). The two stages were separated by an increased subsidence (≥0.2 mm/yr) that drowned a large part of the N070°E primary edifice. The two identified volcano-tectonic stages are reflected also in the geochemical evolution of emitted magmas, which were moderately silica-undersaturated in Stage 1 and moderately to highly silica-undersaturated in Stage 2. Silica undersaturation increases with time up to the olivine melilitite field, together with enrichments in Ca, P, and incompatible trace elements, suggesting the increasing contribution of a metasomatized mantle in melts. The coeval changes of construction orientations and magmas compositions of Mohéli suggest a modification in the tectonics of the Comoros related to magmatism at about 2 Ma. The most recent volcanic morphology investigated is an olivine nephelinite lava flow on the north coast of the island dated at 8 ± 2 ka. This finding of Holocene volcanism on Mohéli implies that the entire Comoros archipelago should be considered as an active zone in ...