The Mantle Fe3+/ΣFe Ratio Has Doubled Since the Early Archean

The mantle’s redox properties play a pivotal role in regulating the exchange of redox budget between Earth’s deep interior and surface, ultimately influencing the accumulation of atmospheric oxygen and the evolution of life. However, how mantle redox state developed, particularly the mantle source associated with mid-ocean ridge-like settings, remains a subject of ongoing debate. Here, we employed thermodynamic-thermomechanical numerical simulations to explore the redox properties of melts formed under mid-ocean ridge-like settings in both Archean and modern conditions. The results of these simulations were systematically compared with an extensive database of mid-ocean ridge-like rocks, dating back as far as 3.8 Ga, to reconstruct the mantle’s redox evolution since the early Archean. This reconstruction utilized a novel and reliable redox proxy, the whole-rock Fe³⁺/ΣFe ratio, by integrating forward numerical modeling with thermodynamic inversion based on natural observations. This ratio is defined as the primary proxy for redox budget variations under mantle reference conditions, especially when the influence of other minor redox-sensitive elements (e.g., carbon, sulfur) is negligible. Our findings demonstrate that the mantle’s average Fe³⁺/ΣFe ratio has approximately doubled since the early Archean. Moreover, our calculations suggest that the ancient ultra-low-oxygen-fugacity mantle found in modern oceanic lithosphere results from an initially reduced origin, rather than deep and hot partial melting. By linking the non-monotonic evolution to geological evidence of tectonic activity, we suggest that the mantle’s redox history may reflect significant tectonic reorganization events. Our findings highlight the intrinsic coupling between Earth’s oxygen-rich environment and tectono-magmatic processes.