Zena Younes - From Periclase to Wüstite: tracing thermal transport across the MgO–FeO system at lower mantle conditions

The thermal state of Earth's deep interior governs mantle convection, core cooling, and the planet's long-term evolution. Yet the thermal conductivity of lower mantle materials remains one of the largest uncertainties in models of deep Earth heat transport. This seminar presents new experimental constraints on the thermal transport properties of the MgO–FeO binary system and on the melting behaviour of FeO under conditions relevant to the lowermost mantle.
Using X-ray free-electron laser experiments at the European XFEL,  the thermal response of the MgO- FeO solid binary solution at simultaneous high pressures and temperatures was measured. By combining time-resolved X-ray diffraction with finite-element thermal modelling, thermal conductivity as a function of composition, pressure, and temperature across the MgO–FeO system was determined.
The results reveal a strong compositional dependence of thermal transport. Initial iron substitution suppresses thermal conductivity through enhanced phonon scattering, whereas Fe-rich compositions exhibit a partial recovery, suggesting an increasing contribution from electronic heat transport under extreme conditions. These findings provide new constraints on the efficiency of heat transfer in chemically heterogeneous regions of the lower mantle.
I also present new measurements of the FeO melting curve obtained using laser-heated diamond anvil cell experiments coupled with phase-contrast imaging. The results indicate that FeO-rich melts may remain stable at core–mantle boundary conditions, lending support to models in which such melts contribute to the formation of ultra-low velocity zones.
Together, these experiments bridge the MgO and FeO endmembers, offering new insights into heat transport, melting, and chemical heterogeneity in Earth's deepest mantle.