Rise of mantle oxidation by Neoarchean subduction in the North China Craton

Abstract

The Archean mantle redox state played an important role in degassing of the Earth's interior and thus influenced atmospheric oxygen levels of the early Earth. But it is unclear if any parts of the uppermost mantle were significantly oxidized by a certain point in the Archean. Here, we investigate oxygen fugacity (fO₂) of Archean (> 2535–2517 Ma) peridotites in the North China Craton. Petrology and geochemistry reveal that they experienced strong Neoarchean subduction-related metasomatism. These Neoarchean subduction-metasomatized peridotites record fO₂ of ΔFMQ +1.3 ± 0.4 (SD) [relative to the fayalite-magnetite-quartz (FMQ) buffer], which are more oxidized than the Archean ambient mantle, but similar to the modern sub-arc mantle. We propose that this Neoarchean rise of mantle oxidation in the North China Craton was induced by plate subduction, during which the Neoarchean sub-arc mantle in the North China Craton could have been metasomatized and oxidized, and its oxygen fugacity was increased. This process may have had connections with the Great Oxidation Event in the Early Proterozoic.