A groundbreaking investigation into the mantle dynamics beneath the Comoros archipelago, specifically Mayotte and its newly formed submarine volcano Fani Maoré, has revealed compelling evidence of surviving Hadean mantle materials, notably bridgmanite, retained within our planet’s deep interior. This study, driven by extraordinary geochemical and isotopic analyses, sheds unprecedented light on Earth’s earliest history and its deep mantle composition, challenging long-held beliefs about mantle homogeneity and introducing fresh perspectives on primordial Earth reservoirs.
The Comoros archipelago, an expression of a profound mantle plume, comprises volcanic islands arranged from west to east with Mayotte standing prominent as the oldest volcanic center. The submarine volcanic activity represented by Fani Maoré, discovered erupting recently between 2018 and 2021 east of Mayotte, serves as a unique natural laboratory. The eruptive materials from this region, chiefly basanites from Fani Maoré and both basanites and phonolites from Petite-Terre, were meticulously collected during oceanographic expeditions, enabling high-precision isotope studies aimed at probing Earth’s ancient mantle components.
In the clean laboratory setting of the Institut de Physique du Globe de Paris, scientists refined rigorous chemical separation techniques to isolate neodymium (Nd) isotopes with exquisite precision, integral to discerning subtle radiogenic variations. Employing state-of-the-art thermal ionization mass spectrometry, the team measured isotopic ratios for various Nd isotopes, leveraging multiple lines of acquisition and careful correction protocols to overcome potential interferences from samarium (Sm) and cerium (Ce). This approach achieved reproducibility at sub-part-per-million levels, enabling detection of minute isotopic anomalies reflective of ancient mantle processes.
The study’s analyses underscored a statistically significant positive anomaly in (^{142})Nd in lavas from Fani Maoré compared to the terrestrial reference standard and Mayotte samples. This anomaly, while subtle, persists beyond analytical uncertainty and aligns with expectations of early Earth differentiation. It points toward the presence of mantle source components enriched in (^{142})Nd, likely originating from the early decay of the now-extinct (^{146})Sm, underscoring the survival and contribution of Hadean mantle material within the plume source.
Radiogenic isotope systematics and trace-element chemistry reveal that the isotope anomaly is disconnected from common geochemical proxies such as Nb/Th, La/Sm, and Ba/Th ratios. This decoupling suggests that the (^{142})Nd isotopic signature marks a primordial reservoir distinct from processes influencing trace element enrichment, highlighting a complex mantle structure with preserved ancient components that do not necessarily correlate with other isotopic or elemental signatures.
Laboratory experiments simulating magma ocean crystallization under extreme pressure and temperature conditions characteristic of Earth’s lower mantle have provided crucial partition coefficients for Sm and Nd between bridgmanite and melt. Using laser-heated diamond anvil cells, researchers conducted fractional crystallization experiments at pressures between 53 and 97 GPa and temperatures exceeding 3,000 K. Results indicate significantly enhanced partitioning of Nd and Sm into bridgmanite under these conditions, accentuating the role of bridgmanite as a dominant host phase for rare earth elements during magma ocean solidification.
Modeling magma ocean fractional crystallization revealed that early crystallizing bridgmanite exhibits elevated Sm/Nd ratios, which result in radiogenic (^{142})Nd anomalies that could persist over geological timescales. Calculations predict that even a modest 10% incorporation of such Hadean bridgmanite into the modern mantle source region of Fani Maoré could reproduce the observed isotopic anomalies. However, disparities in accompanying (^{143})Nd isotopic ratios necessitate the inclusion of a geochemically enriched low-Sm/Nd component, likely recycling sedimentary material with no (^{142})Nd anomaly, to fully resolve the isotopic signatures measured.
Alternative scenarios involving the incorporation of mantle material depleted by early continental crust extraction were also evaluated. These depleted reservoirs, formed within the first few hundred million years of Earth’s history, exhibit high (^{142})Nd signatures but require unrealistically large proportions in the mantle source and an additional enriched component to reconcile the (^{143})Nd data. Consequently, while theoretically plausible, such scenarios bear low likelihood due to constraints on the survival and density-driven redistribution of upper mantle residues into the lower mantle.
The study further considers the involvement of Hadean felsic materials, such as the well-studied Isua noritic dykes bearing enriched (^{142})Nd and strongly negative (^{143})Nd signatures, in mantle source mixing. Mass balance calculations demonstrate that their geochemical imprints cannot account for the combined positive (^{142})Nd and (^{143})Nd values in Fani Maoré lavas, eliminating this source as a plausible contributor to the associated isotopic anomalies.
Cumulatively, these findings unveil an extraordinary glimpse into Earth’s formative eons, revealing that Hadean mantle bridgmanite can survive mantle convection and contribute measurably to modern ocean island basalt sources. The preservation of such primordial material challenges conventional paradigms of mantle homogenization and underscores the intricate complexity and longevity of early-formed reservoirs hidden deep within Earth’s interior.
This research propels our understanding of mantle geochemistry forward, presenting compelling evidence that reconciles ancient isotopic anomalies with physical mineralogical processes in the deep Earth. The discovery of Hadean bridgmanite signatures in a present-day mantle plume sets a new benchmark for geochemical investigations of mantle evolution and calls for renewed interrogation of plume sources worldwide in the quest to decode Earth’s earliest differentiation history.
As a testament to interdisciplinary collaboration, the study masterfully combines advanced isotope geochemistry, high-pressure mineral physics, petrological modeling, and oceanographic fieldwork, illustrating how grasping the nuances of ancient planetary processes demands a convergence of cutting-edge analytical and experimental techniques.
Future directions inspired by this study could involve expanding high-precision isotope analyses across a broader suite of ocean island basalts to identify other hotspots harboring relic Hadean signatures. Additionally, enhanced experiments simulating deep mantle crystallization at varying pressures and compositions could refine models of early Earth differentiation and mantle dynamics.
These revelations not only enrich our comprehension of Earth’s formative period but also have broader implications for planetary science, potentially informing models of terrestrial planet formation and differentiation in our solar system and beyond.
Subject of Research: Investigating the presence of ancient Hadean bridgmanite in the mantle source of modern ocean island basalts from the Comoros archipelago, particularly Fani Maoré.
Article Title: Hadean bridgmanite in the source of a present-day ocean island.
Article References:
Israel, C., Chauvel, C., Inglis, E. et al. Hadean bridgmanite in the source of a present-day ocean island. Nature (2026). https://doi.org/10.1038/s41586-026-10719-w
