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

## TL;DR

The Earth's mantle has become significantly more oxidized since the early Archean, as shown by changes in the Fe³⁺/ΣFe ratio in mid-ocean ridge rocks.

## Contribution

A doubling of the mantle's Fe³⁺/ΣFe ratio since the early Archean is revealed through numerical modeling and global rock data.

## Key findings

- The mantle's average Fe³⁺/ΣFe ratio has approximately doubled since the early Archean.
- Ultra-low-oxygen-fugacity mantle domains in modern oceanic lithosphere reflect an initially reduced origin.
- Earth's oxygenation and tectono-magmatic evolution may be coupled.

## 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.

Numerical modeling combined with a global rock database shows that the Fe³⁺/ΣFe ratio in MORB mantle sources has doubled since the early Archean, suggesting a potential link between mantle redox evolution and Earth’s tectonic activity.