Recycled carbonate-induced oxidization of the convective mantle beneath Jiaodong, Eastern China

The redox state, often expressed as oxygen fugacity (fO(2)), is a fundamental parameter controlling geochemical and geodynamic processes. Recent studies have revealed highly variable convective-mantle fO(2) values, but causes of the variability are poorly understood. High fO(2) values of up to 1.6 log units above the Fayalite-Magnetite-Quartz (FMQ) buffer in Cenozoic Jiaodong basalts of eastern China vary as functions of whole-rock and olivine compositions, with strongly alkaline rocks being more oxidized than alkaline varieties, and with the observed fO(2) variations of the basalts most likely reflecting those of the source. Recycled oceanic-crust carbonates occur throughout sources of Cenozoic basalts and may have acted as oxidants in mantle oxidation. We suggest that the melting of a carbonate-bearing peridotite source at depths of similar to 300 km generated the strongly oxidized alkaline basalts, whereas melting of a pyroxenite source at depths of similar to 100 km produced the weakly alkaline basalts, with the higher oxidation state of the deeper convective mantle likely resulting from differential melting of various components with unique fO(2) values. This study provides a robust petrological link between mantle oxidation and geochemical recycling, which is key to understanding Earth's evolution and geophysical anomalies in the deep mantle. (C) 2020 Elsevier B.V. All rights reserved.