Partitioning of Oxygen Between Ferropericlase and Earth's Liquid Core
Partitioning of Oxygen Between Ferropericlase and Earth's Liquid Core
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DOI：
10.1029/2018gl077758
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发表时间：
2018-06
影响因子：
5.2
通讯作者：
Christopher J. Davies;M. Pozzo;David Gubbins;Dario Alfè
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文献类型：
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作者：
Christopher J. Davies;M. Pozzo;David Gubbins;Dario Alfè
地核和地幔底部之间的氧转移对于确定核幔边界（CMB）两侧分层的化学和性质非常重要。以前的研究发现，当Fe-O液体与代表性的下地幔物质平衡时，氧进入金属。然而，尚未在CMB压力-温度条件下进行实验。在这里，我们使用密度泛函理论，以获得在CMB条件下的液态Fe-O-Si金属和铁方镁石之间的氧分配的第一个估计。我们的方法成功地再现了实验得出的分区数据在134 GPa和3200 K，而我们的计算表明，随着温度和压力的增加，较弱的增加，与以前的工作相一致的氧分配到金属的强烈增加。在135 GPa和4000-4700 K的CMB条件下，氧分配到金属中高于以前的估计，并随着金属氧浓度的增加而强烈增加。下地幔化学边界层的分析表明，通过固体的氧运输是严重限制，即使增强分区，是不可能解释的厚度稳定分层层以下的CMB推断地震。然而，如果下地幔在早期熔融，如具有高热导率的核心演化模型所示，则质量通量和稳定层厚度显着增加。
Transfer of oxygen between Earth's core and lowermost mantle is important for determining the chemistry and nature of stratification on both sides of the core‐mantle boundary (CMB). Previous studies have found that oxygen enters the metal when Fe‐O liquid equilibrates with representative lower mantle materials. However, experiments have not yet been conducted at CMB pressure‐temperature conditions. Here we use density functional theory to obtain the first estimates of oxygen partitioning between liquid Fe‐O‐Si metals and ferropericlase at CMB conditions. Our method successfully reproduces experimentally derived partitioning data at 134 GPa and 3200 K, while our calculations show a strong increase of oxygen partitioning into metal with temperature and a weaker increase with pressure, consistent with previous work. At CMB conditions of 135 GPa and 4000–4700 K oxygen partitioning into metal is higher than previous estimates and increases strongly with metal oxygen concentration. Analysis of the lower mantle chemical boundary layer shows that oxygen transport through the solid is severely limited even with the enhanced partitioning and is unlikely to explain the thickness of a stably stratified layer below the CMB inferred from seismology. However, if the lower mantle was molten in early times, as suggested by core evolution models with high thermal conductivity, then the mass flux and stable layer thickness are significantly increased.