Ferrous iron partitioning in the lower mantle
Ferrous iron partitioning in the lower mantle
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DOI：
10.1016/j.pepi.2016.05.008
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发表时间：
2016-08-01
影响因子：
2.3
通讯作者：
Brodholt, John P.
中科院分区：
文献类型：
--
作者：
Muir, Joshua M. R.;Brodholt, John P.
我们利用密度泛函理论（DFT）研究了下地幔条件下铁橄榄石和布里奇曼石之间亚铁的分配情况。为了研究三个主要变量——压力、温度和浓度的影响，我们将压力在0到150吉帕之间、温度在1000到4000开尔文之间以及总铁含量在0到100%之间进行了变化。我们发现温度升高会使分配系数（K - D）增大，铁浓度增加会使K - D降低，而压力既可能使K - D增大也可能使其减小。我们发现在下地幔条件下，随着深度增加，K - D从约0.32缓慢降低到0.06。我们还发现，由于核幔边界（CMB）附近温度大幅升高，在最下部的地幔中K - D急剧上升到0.15。自旋转变对铁橄榄石的活度有很大影响，这导致K - D随压力呈峰状变化。尽管在地幔中K - D看似有很大变化，但实际上这导致两相中的总铁含量变化相对较小，铁橄榄石中的铁含量（X - Fe(fP)）在核幔边界处再次降低到约0.28之前，从约0.20到0.35变化，而布里奇曼石中的铁含量（X - Fe(bd)）在下地幔中始终保持在约0.04 - 0.07的相当稳定的值。对于超低速区（ULVZs）所推测的极高铁浓度，铁非常强烈地分配到铁橄榄石中。（C）2016作者。由爱思唯尔出版集团出版。
We used density functional theory (DFT) to examine the partitioning of ferrous iron between periclase and bridgmanite under lower mantle conditions. To study the effects of the three major variables - pressure, temperature and concentration - these have been varied from 0 to 150 GPa, from 1000 to 4000 K and from 0 to 100% total iron content. We find that increasing temperature increases K-D, increasing iron concentration decreases K-D, while pressure can both increase and decrease K-D. We find that K-D decreases slowly from about 0.32 to 0.06 with depth under lower mantle conditions. We also find that K-D increases sharply to 0.15 in the very lowermost mantle due to the strong temperature increases near the CMB. Spin transitions have a large effect on the activity of ferropericlase which causes K-D to vary with pressure in a peak-like fashion. Despite the apparently large changes in K-D through the mantle, this actually results in relatively small changes in total iron content in the two phases, with X-Fe(fP), ranging from about 0.20 to 0.35, before decreasing again to about 0.28 at the CMB, and X-Fe(bd) has a pretty constant value of about 0.04-0.07 throughout the lower mantle. For the very high Fe concentrations suggested for ULVZs, Fe partitions very strongly into ferropericlase. (C) 2016 The Authors. Published by Elsevier B.V.