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

Abstract

How mantle redox state developed, particularly the mantle source associated with mid-ocean ridge-like settings, remains a subject of ongoing debate. Here, we employ thermodynamic-thermomechanical numerical simulations to explore the redox properties of melts formed under mid-ocean ridge-like settings in both Archean and modern conditions. By comparing these results with a global database of mid-ocean ridge-like rocks extending back to 3.8 Ga, we reconstruct the mantle's redox evolution since the early Archean. Using the whole-rock Fe³⁺/ΣFe ratio as a robust redox proxy, derived from integrated numerical modeling and thermodynamic inversion, we find that the mantle's average Fe³⁺/ΣFe ratio has approximately doubled since the early Archean. Our calculations further indicate that ultra-low-oxygen-fugacity mantle domains in modern oceanic lithosphere reflect an initially reduced origin rather than deeper or hotter melting. Our results suggest that Earth's oxygenation and tectono-magmatic evolution may have been coupled.