Iron Content-Dependence of Ferropericlase Elastic Properties Across the Spin Crossover From Novel Experiments and Machine Learning

The iron spin crossover in (Mg_1-xFe_x)O ferropericlase causes changes to its physical properties that are expected to affect seismic velocities in Earth's lower mantle. We present new time-resolved pressure-volume measurements of iron-rich ferropericlase (x_Fe = 0.40, 0.59) and combine the results with literature data with x_Fe = 0.04–0.6 to investigate the dependence of ferropericlase elastic properties on iron content. We infer the relationship between unit-cell volume, pressure and iron content directly from the data by training Mixture Density Networks and derive bulk modulus, density and bulk sound velocity from the outputs. This allows us to constrain the effect of the spin crossover on these properties and estimate their uncertainties for different iron contents. Our findings indicate that the spin crossover may significantly alter the physical properties of ferropericlase in iron-enriched regions in the lowermost mantle, with implications for the interpretation of seismic heterogeneities observed near the core-mantle boundary.