Partitioning of Iron Between Liquid and Crystalline Phases of (Mg,Fe)O
Partitioning of Iron Between Liquid and Crystalline Phases of (Mg,Fe)O
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DOI：
10.1029/2022gl099116
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发表时间：
2022-08-28
影响因子：
5.2
通讯作者：
Stixrude, Lars
中科院分区：
文献类型：
--
作者：
Braithwaite, James;Stixrude, Lars
晶体和共存液体之间的密度对比是理解岩浆海演化的关键。虽然在地幔的压力范围内，大多数氧化物和硅酸盐系统中的晶体仍然比等化学液体密度大，但元素的分配，特别是丰富的重元素，如铁，可以改变浮力。采用基于自旋极化密度泛函理论和绝热开关的分子动力学模拟，确定了液体和结晶中铁取代的自由能（Mg,Fe）O及其分布系数。我们发现铁在地幔压力范围内的分布系数小于0.3时是不相容的。我们发现，在超过50 GPa的压力下，晶体相对于共存的液体是浮力的。高自旋向低自旋的转变对分布系数有重要影响，当压力达到80 GPa时，分布系数随压力的增加而减小，随着压力的进一步增加而增大。
The density contrast between crystals and coexisting liquids is key to understanding the evolution of the magma ocean. While crystals remain denser than isochemical liquids in most oxide and silicate systems over the pressure range of Earth's mantle, element partitioning, particularly of abundant heavy elements such as iron, can alter the buoyancy. We use molecular dynamics simulations based on spin-polarized density functional theory and adiabatic switching to determine the free energy of iron substitution in liquid and crystalline (Mg,Fe)O and the distribution coefficient. We find that iron is strongly incompatible with a distribution coefficient less than 0.3 over the mantle pressure range. We find that the crystal is buoyant with respect to coexisting liquid at pressures exceeding 50 GPa. The high-spin to low-spin transition has an important influence on the distribution coefficient, which decreases with increasing pressure up to 80 GPa, and then increases on further increase of pressure.