Disproportion and spin crossover of iron in planetary magma oceans

The redox state established in deep magma oceans influences the formation of distinct geochemical domains and early atmospheres on rocky planets. The estimated mean pressure (P) of silicate-alloy equilibria in Earth’s magma ocean reaches >60 GPa, but existing experimental constraints on the iron (Fe) redox speciation applicable to magma oceans are limited to 28 GPa and yield conflicting predictions regarding the stabilization of oxidized species in deep magma oceans.

This study aims to establish the effect of P on Fe disproportionation reactions and spin crossover of Fe in dense silicate melt up to 80 GPa. We will measure the valences and spin states of Fe in silicate glasses quenched from laser-heated diamond anvil cell (DAC) experiments using the recently upgraded synchrotron Mössbauer spectroscopy (SMS) beamline ID14 ESRF, with a spatial resolution of ~800 nm (FWHM). We also seek to detect any Fe metal in the quenched silicate melts formed through disproportionation of Fe2+.