Fe isotope variations in rocky bodies reveal fundamental information about planetary evolution. However, experimental results have come to contradictory conclusions on the equilibrium Fe isotope fractionation between metal and silicate during core-mantle differentiation. Many different processes, including evaporation, core formation, partial melting and disproportion of mantle silicate, have been consequently proposed to explain the observed Fe isotope variations in rocky solar system bodies. Here we perform molecular dynamics simulations and find that the anharmonicity in iron strongly decreases the force constant of Fe at low pressures (<∼50 GPa), which even reverses the equilibrium Fe isotope fractionation between metal and silicate. We conclude that pyrolitic melt is always enriched in heavy Fe isotopes relative to liquid Fe-alloys, no matter what pressure. Therefore core-mantle differentiation will play a significant role in explaining the heavy Fe isotope compositions of the mantles of some rocky bodies (e.g., Earth, the ureilite parent body, and possibly the asteroid Vesta). As all previously proposed processes for Fe isotope fractionation can only enrich the mantle-derived rocks in heavy Fe isotopes, the near/sub-chondritic Fe isotope signatures of Mars and the aubrite parent body thus imply that iron sulfide enriched in light Fe isotopes may significantly contribute to the iron components of those meteoritic samples.

中文翻译：

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岩体核幔分异过程中金属和硅酸盐之间的铁同位素分馏


岩石体中铁同位素的变化揭示了行星演化的基本信息。然而，实验结果对核幔分异过程中金属与硅酸盐之间的铁同位素平衡分馏得出了相互矛盾的结论。因此，人们提出了许多不同的过程，包括蒸发、核心形成、部分熔融和地幔硅酸盐的歧化，来解释在岩石太阳系天体中观察到的铁同位素变化。在这里，我们进行了分子动力学模拟，发现铁中的非和谐性强烈降低了低压（<∼50 GPa）下Fe的力常数，甚至逆转了金属和硅酸盐之间的平衡Fe同位素分馏。我们得出的结论是，无论压力如何，热解熔体相对于液态铁合金总是富含重铁同位素。因此，核心-地幔分异将在解释一些岩石天体（例如地球、尿素岩母体，可能还有小行星灶神星）地幔的重铁同位素组成方面发挥重要作用。由于所有先前提出的铁同位素分馏过程只能富集地幔衍生岩石中​​的重铁同位素，因此火星和赤赤铜矿母体的近/亚球粒状铁同位素特征意味着富含轻铁同位素的硫化铁可能显着有助于这些陨石样本的铁成分。