Volcanism in the Comoros Archipelago, Madagascar, and the East African Rift: What is the link?

Abstract The Comoros archipelago located in the western Indian Ocean has been a topic of debate for ca. 50 years regarding its origin. Various mechanisms have been proposed to explain its formation, ranging from the impact of a mantle plume to the development of a plate boundary between the Somalia and Lwandle plates. Determining the timing of the volcanic activity is crucial to understanding the archipelago's origin. Despite recent geochronological studies, the age of the initial volcanic eruptions on the islands remains uncertain due to the difficulty of accessing the earliest lavas. This study uses high-quality seismic reflection profiles and regional stratigraphy to identify the first volcanic series that marked the onset of volcanism on each island of the Comoros Archipelago. Our findings reveal that localized volcanic activity began ca. 32 Ma at Zélée and Geyser banks and Mayotte edifice, the eastern portions of the archipelago, much earlier than previously believed. Volcanism spread across the Comoros archipelago ca. 9–8 Ma, from the northern part of the Mayotte edifice to Mohéli Island in the west. Ca. 4 Ma, volcanic activity occurred on Anjouan Island and the Jumelles seamounts, followed by Grande Comore Island ca. 2 Ma. This progression of ages from east to west indicates a chronological sequence over time. The timing of volcanic activity in the Comoros archipelago is similar to the magmatism evolution documented at Madagascar and along the East African Rift System (EARS). Magmatic activity began in the late Oligocene, followed by quiescence during the middle Miocene, and resumed in the late Miocene, coinciding with widespread deformation along the EARS, including its offshore branches and Madagascar. Our study shows that the regional tectonic control of volcanic activity in the Comoros archipelago began during the early Miocene, thereby suggesting that the Comoros archipelago developed as an offshore branch of the EARS south of the Somalian plate at that time.