First‐Principles Study of FeO2Hx Solid and Melt System at High Pressures: Implications for Ultralow‐Velocity Zones
First‐Principles Study of FeO2Hx Solid and Melt System at High Pressures: Implications for Ultralow‐Velocity Zones
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DOI：
10.1029/2019jb017376
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发表时间：
2019-05
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影响因子：
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通讯作者：
Jie Deng;B. Karki;D. Ghosh;Kanani K. M. Lee
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文献类型：
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作者：
Jie Deng;B. Karki;D. Ghosh;Kanani K. M. Lee
黄铁矿型FeO_2H_x(P相)由于其低地震速度和高密度，最近被认为是解释超低速带的一种可能的替代方案。本文报道了用第一性原理分子动力学方法模拟高压下P相的同组分熔化温度和熔体性质的结果。结果表明，P相可能在核幔边界附近熔融。与等化学P相相比，液态FeO_2H_x具有较小的密度和体积声速。因此，相对少量的液态FeO_2Hx可以解释观测到的超低速带的地震异常。然而，要将液态FeO_2Hx保持在防止压实的超低速区内，需要特殊的物理条件，如固体基质的相对较高的粘度和/或上覆地幔的强烈对流。
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.