Hadean bridgmanite in the source of a present-day ocean island

Geological context of the samples The Comoros archipelago is the surface manifestation of a deep plume. The main islands that make up this archipelago are Grande Comore, Mohéli and Anjouan, as well as the islands that constitute Mayotte, namely Grande-Terre and Petite-Terre, from west to east 53 . Of these, Mayotte corresponds to the oldest volcanic activity, with the first subaerial eruption occurring about 11 million years ago (Ma). However, its volcanic activity has alternated between periods of active and quiescent phases, shaping its two islands of Grande-Terre and Petite-Terre 54 . The most recent volcanic activity was observed on Petite-Terre and is Holocene 54 , 55 in age. Between June 2018 and January 2021, a new submarine volcano called Fani Maoré erupted approximately 55 km east of Mayotte, representing the most recent volcanic expression of the plume (see Fig. 1 in ref. 56 and Extended Data Fig. 1 ). The 2018–2021 crisis that led to the formation of Fani Maoré is associated with a volcanic ridge that extends westwards towards Petite-Terre 56 , 57 . In this context, we analysed 13 samples from the new submarine volcano Fani Maoré and eight samples from the eastern flank of Petite-Terre, Mayotte (Extended Data Fig. 1 ). These samples were collected during a series of oceanographic cruises between 2018 and 2021 (MAYOBS1, MAYOBS2, MAYOBS4 and MAYOBS15 (refs. …