Abstract The liquid metal–liquid silicate partitioning of molybdenum and tungsten during core formation must be well-constrained in order to understand the evolution of Earth and other planetary bodies, in particular because the Hf–W isotopic system is used to date early planetary evolution. The partition coefficients DMo and DW have been suggested to depend on pressure, temperature, silicate and metal compositions, although previous studies have produced varying and inconsistent models. Additionally, the high cationic charges of W and Mo in silicate melts make their partition coefficients particularly sensitive to oxygen fugacity. We combine 48 new high pressure and temperature experimental results with a comprehensive database of previous experiments to re-examine the systematics of Mo and W partitioning, and produce revised partitioning models from the large combined dataset. W partitioning is particularly sensitive to silicate and metallic melt compositions and becomes more siderophile with increasing temperature. We show that W has a 6+ oxidation state in silicate melts over the full experimental fO2 range of ΔIW -1.5 to -3.5. Mo has a 4+ oxidation state and its partitioning is less sensitive to silicate melt composition, but also depends on metallic melt composition. DMo stays approximately constant with increasing depth in Earth. Both W and Mo become more siderophile with increasing C content of the metal: we therefore performed experiments with varying C concentrations and fit epsilon interaction parameters: e C Mo = -7.03 ± 0.30 and e C W = -7.38 ± 0.57. W and Mo along with C are incorporated into a combined N-body accretion and core–mantle differentiation model, which already includes the major rock-forming elements as well as S, moderately and highly siderophile elements. In this model, oxidation and volatility gradients extend through the protoplanetary disk so that Earth accretes heterogeneously. These gradients, as well as the metal–silicate equilibration pressure, are fitted using a least squares optimisation so that the model Earth-like planet reproduces the composition of the Bulk Silicate Earth (BSE) across 17 simulated element concentrations (Mg, Fe, Si, Ni, Co, Nb, Ta, V, Cr, S, Pt, Pd, Ru, Ir, W, Mo, and C). The effects of the interaction of W and Mo with Si, S, O, and C in metal are included. Using this model with six separate terrestrial planet accretion simulations, we show that W and Mo require the early accreting Earth to be sulfur-depleted and carbon-enriched so that W and Mo are efficiently partitioned into Earth’s core and do not accumulate in the mantle. If this is the case, the produced Earth-like planets possess mantle compositions matching the BSE for all simulated elements. However, there are two distinct groups of estimates of the bulk mantle’s C abundance in the literature: low (∼100 ppm), and high (∼800 ppm), and all six models are consistent with the higher estimated carbon abundance. The low BSE C abundance would be achievable when the effects of the segregation of dispersed metal droplets produced in deep magma oceans by the disproportionation of Fe2+ to Fe3+ plus metallic Fe is considered.

中文翻译：

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W 和 Mo 的金属-硅酸盐分配以及碳在控制它们在大块硅酸盐地球中的丰度中的作用

摘要 为了了解地球和其他行星体的演化，必须很好地限制地核形成过程中钼和钨的液态金属-液态硅酸盐分配，特别是因为 Hf-W 同位素系统用于确定早期行星演化的年代。已建议分配系数 DMo 和 DW 取决于压力、温度、硅酸盐和金属成分，尽管之前的研究产生了不同且不一致的模型。此外，硅酸盐熔体中 W 和 Mo 的高阳离子电荷使其分配系数对氧逸度特别敏感。我们将 48 个新的高压和高温实验结果与先前实验的综合数据库相结合，重新审视 Mo 和 W 分配的系统学，并从大型组合数据集中生成修订的分区模型。W 分配对硅酸盐和金属熔体成分特别敏感，并且随着温度升高变得更加亲铁。我们表明，在 ΔIW -1.5 到 -3.5 的整个实验 fO2 范围内，W 在硅酸盐熔体中具有 6+ 氧化态。Mo 具有 4+ 氧化态，其分配对硅酸盐熔体组成不太敏感，但也取决于金属熔体组成。随着地球深度的增加，DMo 基本保持不变。随着金属中 C 含量的增加，W 和 Mo 都变得更加亲铁：因此，我们用不同的 C 浓度进行了实验，并拟合了 epsilon 相互作用参数：e C Mo = -7.03 ± 0.30 和 e CW = -7.38 ± 0.57。W 和 Mo 连同 C 被纳入一个组合的 N 体吸积和核幔分异模型，该模型已经包括主要的造岩元素以及 S，中度和高度亲铁元素。在这个模型中，氧化和挥发性梯度通过原行星盘延伸，因此地球不均匀地吸积。这些梯度以及金属硅酸盐平衡压力使用最小二乘法优化拟合，以便模拟类地行星在 17 种模拟元素浓度（Mg、Fe、Si）中重现大块硅酸盐地球 (BSE) 的组成、Ni、Co、Nb、Ta、V、Cr、S、Pt、Pd、Ru、Ir、W、Mo 和 C)。包括 W 和 Mo 与金属中的 Si、S、O 和 C 相互作用的影响。将此模型与六个独立的类地行星吸积模拟一起使用，我们表明 W 和 Mo 需要早期吸积的地球贫硫和富碳，以便 W 和 Mo 有效地分配到地核中并且不会在地幔中积累。如果是这种情况，则生成的类地行星的地幔成分与所有模拟元素的 BSE 相匹配。然而，文献中对大块地幔的 C 丰度有两组不同的估计：低（~100 ppm）和高（~800 ppm），并且所有六个模型都与较高的估计碳丰度一致。当考虑到由 Fe2+ 歧化为 Fe3+ 加金属 Fe 时在深部岩浆海洋中产生的分散金属液滴的分离效应时，可以实现低 BSE C 丰度。