Melting of (Mg, Fe)O Ferropericlase at High Pressure (> 40 GPa)

Abstract:

(Mg, Fe)O ferropericlase is the second most abundant mineral in Earth’s lower mantle. Previous laser-heated diamond-anvil cell (LHDAC) experiments on ferropericlase yielded an MgO melting curve consistent with ab initio predictions and suggested that FeO forms a complete solid solution with MgO at least up to ~40 GPa [Du and Lee, 2014]. But the melting behavior of ferropericlase at pressures greater than 40 GPa remains poorly constrained. We have performed LHDAC experiments using in situ two-dimensional multi-wavelength imaging radiometry and ex situ chemical and textural analyses of samples melted at ~70 GPa. Our results suggest that ferropericlase deviates from an ideal solid solution to possibly eutectic behavior, assuming the MgO melting curve is still predicted well by ab initio computational methods.

Additionally, we find an offset between the centers of the two-dimensional maps of emissivity and temperature. A tentative interpretation is that the (Mg, Fe)O becomes metallic at high pressures and temperatures [Ohta et al., 2014; Ovchinnikov, 2011; Ovchinnikov et al., 2012] and thus the intensity of light absorbed by the solid surrounding the molten region is strongly wavelength dependent, leading to the uneven variation in light intensity detected by the multi-wavelength imaging radiometric temperature measurement system and consequently abnormal correlation between temperature and emissivity.