The constant oxidation state of Earth’s mantle since the Hadean

Abstract

Abstract Determining the evolutionary history of mantle oxygen fugacity (fo2) is crucial, as it controls the fo2 of mantle-derived melts and regulates atmospheric composition through volcanic outgassing. However, the evolution of mantle fo2 remains controversial. Here, we present a comprehensive dataset of plume-derived komatiites, picrites, and ambient mantle-derived (meta)basalts, spanning from ~3.8 Ga to the present, to investigate mantle thermal and redox states evolution. Our results indicate that fo2 of both mantle plume-derived and ambient mantle-derived melts was lower during the Archean compared to the post-Archean period. This increase in the fo2 of mantle-derived melts over time correlates with decreases in mantle potential temperature and melting depth. By normalizing fo2 to a constant reference pressure (potential oxygen fugacity), we show that the fo2 of both the mantle plume and ambient upper mantle has remained constant since the Hadean. These findings suggest that secular mantle cooling reduced melting depth, increasing the fo2 of mantle-derived melts and contributing to atmospheric oxygenation.