Abstract In the accreting Earth and planetesimals, carbon was distributed between a core forming metallic melt, a silicate melt, and a hot, potentially dense atmosphere. Metal melt droplets segregating gravitationally from the magma ocean equilibrated near its base. To understand the distribution of carbon, its partitioning between the two melts is experimentally investigated at 1.5–6.0 GPa, 1300–2000 °C at oxygen fugacities of −0.9 to −1.9 log units below the iron-wuestite reference buffer (IW). One set of experiments was performed in San Carlos olivine capsules to investigate the effect of melt depolymerization (NBO/T), a second set in graphite capsules to expand the data set to higher pressures and temperatures. Carbon concentrations were analyzed by secondary ionization mass spectrometry (SIMS) and Raman spectra were collected to identify C-species in the silicate melt. Partition coefficients are governed by the solubility of C in the silicate melt, which varies from 0.01 to 0.6 wt%, while metal melts contain ∼7 wt% C in most samples. C solubility in the silicate melt correlates strongly with NBO/T, which, in olivine capsules, is mostly a function of temperature. Carbon partition coefficients DCmetal/silicate at 1.5 GPa, 1300–1750 °C decrease from 640(49) to 14(3) with NBO/T increasing from 1.04 to 3.11. For the NBO/T of the silicate Earth of 2.6, DCmetal/silicate is 34(9). Pressure and oxygen fugacity show no clear effect on carbon partitioning. The present results differ from those of most previous studies in that carbon concentrations in the silicate melt are comparatively higher, rendering C to be about an order of magnitude less siderophile, and the discrepancies may be attributed to differences in the experimental protocols. Applying the new data to a magma ocean scenario, and assuming present day mantle carbon mantle concentrations from 120 to 795 ppm, implies that the core may contain 0.4–2.6 wt% carbon, resulting in 0.14–0.9 wt% of this element for the bulk Earth. These values are upper limits, considering that some of the carbon in the modern silicate Earth has very likely been delivered by the late veneer.

中文翻译：

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地球吸积过程中金属和硅酸盐熔体之间的碳分配

摘要在吸积的地球和小行星中，碳分布在形成金属熔体的核心、硅酸盐熔体和热的、潜在致密的大气之间。金属熔滴在重力作用下从岩浆海洋中分离出来，在其底部附近达到平衡。为了了解碳的分布，在 1.5–6.0 GPa、1300–2000 °C 下，在铁-方铁矿参考缓冲液 (IW) 以下的氧逸度为 -0.9 到 -1.9 log 单位的条件下，对其在两种熔体之间的分配进行了实验研究。一组实验在圣卡洛斯橄榄石胶囊中进行，以研究熔融解聚 (NBO/T) 的影响，第二组实验在石墨胶囊中进行，以将数据集扩展到更高的压力和温度。通过二次电离质谱 (SIMS) 分析碳浓度并收集拉曼光谱以鉴定硅酸盐熔体中的 C 物种。分配系数由 C 在硅酸盐熔体中的溶解度决定，从 0.01 到 0.6 wt%，而金属熔体在大多数样品中含有~7 wt% C。C 在硅酸盐熔体中的溶解度与 NBO/T 密切相关，在橄榄石胶囊中，NBO/T 主要是温度的函数。碳分配系数 DCmetal/硅酸盐在 1.5 GPa，1300–1750 °C 从 640(49) 降低到 14(3)，NBO/T 从 1.04 增加到 3.11。对于2.6的硅酸盐地球的NBO/T，DCmetal/硅酸盐是34(9)。压力和氧逸度对碳分配没有明显影响。目前的结果与大多数先前研究的结果不同，因为硅酸盐熔体中的碳浓度相对较高，使 C 的亲铁性降低了大约一个数量级，差异可能归因于实验方案的差异。将新数据应用于岩浆海洋情景，并假设当今地幔碳地幔浓度为 120 至 795 ppm，意味着核心可能含有 0.4-2.6 wt% 的碳，导致该元素的 0.14-0.9 wt% 为主体地球。这些值是上限，考虑到现代硅酸盐地球中的一些碳很可能是由晚期单板提供的。并且差异可能归因于实验方案的差异。将新数据应用于岩浆海洋情景，并假设当今地幔碳地幔浓度为 120 至 795 ppm，意味着核心可能含有 0.4-2.6 wt% 的碳，导致该元素的 0.14-0.9 wt% 为主体地球。这些值是上限，考虑到现代硅酸盐地球中的一些碳很可能是由晚期单板提供的。并且差异可能归因于实验方案的差异。将新数据应用于岩浆海洋情景，并假设当今地幔碳地幔浓度为 120 至 795 ppm，意味着核心可能含有 0.4-2.6 wt% 的碳，导致该元素的 0.14-0.9 wt% 为主体地球。这些值是上限，考虑到现代硅酸盐地球中的一些碳很可能是由晚期单板提供的。