Abstract This study investigates the partitioning of U and Th between molten metal and silicate liquid (DU and DTh) during Earth’s core-mantle differentiation. We report new Th partition coefficients between chondritic silicate melt and various Fe-rich alloys in the system Fe-Ni-C-S-Si as determined by experiments in a multi-anvil apparatus at 3–8 GPa, 2073–2373 K, and oxygen fugacities from 1.5 to 5 log units below the iron-wustite (IW) buffer. By compiling all existing data on molten metal-silicate liquid partitioning of U and Th, we develop global models of U and Th partitioning between the mantle and core throughout Earth’s accretion. The calculated concentrations in the Bulk Silicate Earth (BSE) are in agreement with previous studies (UBSE = 11.42 ± 0.45 ppb and ThBSE = 43.20 ± 1.73 ppb), whereas the contents of these radioactive elements in the Earth’s core remain negligible. Compared to recent geochemical estimations, the calculated (Th/U)BSE supports EL rather than EH enstatite chondrites as the reduced building blocks of the Earth. Furthermore, we demonstrate that Th is much more sensitive than U to the oxygen content of the metallic phase. To reproduce the Th/U ratio of the BSE within its uncertainties, the oxygen content of the Earth’s core must be lower than 4.0 wt%. By combining other existing constraints, this suggests that the core contains 2.0–4.0 wt% O. The calculations of U and Th concentrations and Th/U in the BSE developed herein can be used as new constraints for determining the concentrations of other refractory lithophile elements in the BSE as soon as their metal-silicate partition coefficients are well constrained over the conditions of core segregation.

中文翻译：

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铀和钍在大块硅酸盐地球中的分配和地球核心的氧含量

摘要 本研究调查了地核-地幔分异过程中熔融金属和硅酸盐液体（DU 和 DTh）之间 U 和 Th 的分配。我们报告了系统 Fe-Ni-CS-Si 中球粒状硅酸盐熔体和各种富铁合金之间的新 Th 分配系数，这是通过在 3-8 GPa、2073-2373 K 和氧逸度下的多砧装置中的实验确定的铁-方氏体 (IW) 缓冲区下方 1.5 到 5 个对数单位。通过汇编有关 U 和 Th 的熔融金属硅酸盐液体分配的所有现有数据，我们开发了整个地球吸积过程中地幔和地核之间 U 和 Th 分配的全球模型。大块硅酸盐 (BSE) 中的计算浓度与之前的研究一致（UBSE = 11.42 ± 0.45 ppb 和 ThBSE = 43.20 ± 1.73 ppb），而地核中这些放射性元素的含量仍然可以忽略不计。与最近的地球化学估计相比，计算出的 (Th/U)BSE 支持 EL 而不是 EH 顽火球粒陨石作为地球的还原构建块。此外，我们证明 Th 对金属相的氧含量比 U 更敏感。为了在其不确定性内重现 BSE 的 Th/U 比，地核的氧含量必须低于 4.0 wt%。通过结合其他现有的约束，这表明核心包含 2.0-4.0 wt% O。