Iron disproportionation in ultramafic silicate melts: Implications for magma ocean redox evolution

The redox state of Earth’s mantle established during early differentiation, has a fundamental influence on early atmospheres and evolution towards habitability. A key process is iron disproportionation in deep magma oceans (28–53 GPa), yet experimental constraints remain limited at high pressures, particularly for ultramafic silicate melts (magma ocean compositions).

We propose to study the pressure dependence of Fe disproportionation in ultramafic melts (10–80 GPa) using synchrotron Mössbauer spectroscopy (SMS) at ID14. A new sample configuration, with natural Fe silicate glass as both pressure medium and thermal insulator, will reduce contaminated SMS signals and contamination. Quenched melts will be analyzed directly in DACs under pressure and along decompression, minimizing air-induced alteration. This allows separation of spectral contribution from disproportionation and spin crossover, yielding the first in situ determination of Fe³⁺/ΣFe in ultramafic melts at high pressures.