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Pyrite-type FeO H (P phase) has recently been suggested as a possible alternative to explain ultralow-velocity zones due to its low seismic velocity and high density. Here we report the results on the congruent melting temperature and melt properties of P phase at high pressures from first-principles molecular dynamics simulations. The results show that P phase would likely be melted near the core–mantle boundary. Liquid FeO H has smaller density and smaller bulk sound velocity compared to the isochemical P phase. As such, relatively small amounts of liquid FeO H could account for the observed seismic anomaly of ultralow-velocity zones. However, to maintain the liquid FeO H within the ultralow-velocity zones against compaction requires special physical conditions, such as relatively high viscosity of the solid matrix and/or vigorous convection of the overlying mantle. 2 x 2 x 2 x 2 x

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Journal of Geophysical Research: Solid Earth

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