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Pyrite-type FeO2Hx (P phase) has recently been suggested as a possible explanation for ultra-low velocity zones (ULVZs) 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 FeO2Hx has smaller density and smaller bulk sound velocity compared to the isochemical P phase. As such, small amounts of liquid FeO2Hx could account for the observed seismic anomaly of ULVZs. However, to maintain the liquid FeO2Hx within the ULVZs against compaction requires special physical conditions, such as relatively high viscosity of the solid matrix and/or vigorous convection of the overlying mantle.more » « less
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Pyrite‐type FeO2Hx (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 FeO2Hx has smaller density and smaller bulk sound velocity compared to the isochemical P phase. As such, relatively small amounts of liquid FeO2Hx could account for the observed seismic anomaly of ultralow‐velocity zones. However, to maintain the liquid FeO2Hx 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.more » « less
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