The formation of diamonds within eclogitic rocks has been widely linked to the fate of carbon during subduction and, therefore, referred to conditions of pressure, temperature, and oxygen fugacity (fo2). Mantle-derived eclogite xenoliths from Udachnaya kimberlite pipes represent a unique window to investigate the formation of carbon-free, graphite–diamond-bearing and diamond-bearing rocks from the Siberian craton. With this aim, we exploited oxy-thermobarometers to retrieve information on the P–T–fo2 at which mantle eclogites from the Siberian craton equilibrated along with elemental carbon. The chemical analyses of coupled garnet and omphacitic clinopyroxene were integrated with data on their iron oxidation state, determined both by conventional and synchrotron 57Fe Mössbauer spectroscopy. The calculated fo2s largely vary for each suite of eclogite samples from 0.10 to − 2.43 log units (ΔFMQ) for C-free eclogites, from − 0.01 to − 2.91 (ΔFMQ) for graphite–diamond-bearing eclogites, and from − 2.08 to − 3.58 log units (ΔFMQ) for diamond-bearing eclogites. All eclogite samples mostly fall in the fo2 range typical of diamond coexisting with CO2-rich water-bearing melts and gaseous fluids, with diamondiferous eclogites being more reduced at fo2 conditions where circulating fluids can include some methane. When uncertainties on the calculated fo2 are taken into account, all samples essentially fall within the stability field of diamonds coexisting with CO2-bearing melts. Therefore, our results provide evidence of the potential role of CO2-bearing melts as growth medium on the formation of coexisting diamond and graphite in mantle eclogites during subduction of the oceanic crust.

中文翻译：

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来自 Udachnaya 金伯利岩管（西伯利亚克拉通）的榴辉岩包体的氧化还原状态测定，对石墨/金刚石的形成有一些影响

榴辉岩中钻石的形成与俯冲过程中碳的命运有着广泛的联系，因此与压力、温度和氧逸度 (fo2) 条件有关。来自 Udachnaya 金伯利岩管的幔源榴辉岩包体代表了一个独特的窗口，可以研究西伯利亚克拉通无碳、含石墨金刚石和含金刚石的岩石的形成。出于这个目的，我们利用氧温度计来检索有关 P-T-fo2 的信息，在该信息中，来自西伯利亚克拉通的地幔榴辉岩与元素碳一起平衡。耦合石榴石和无辉石单斜辉石的化学分析与其铁氧化态的数据相结合，这些数据由常规和同步加速器 57Fe 穆斯堡尔光谱确定。对于每组榴辉岩样品，计算出的 fo2s 在无 C 榴辉岩的 0.10 至 - 2.43 log 单位 (ΔFMQ)、含石墨-金刚石榴辉岩的 - 0.01 至 - 2.91 (ΔFMQ) 和 - 2.08 至 -含金刚石榴辉岩为 3.58 log 单位 (ΔFMQ)。所有榴辉岩样品大部分都在 fo2 范围内，这是钻石与富含 CO2 的含水熔体和气态流体共存的典型特征，而含金刚石榴辉岩在 fo2 条件下被更多地还原，其中循环流体可能包含一些甲烷。当计算 fo2 的不确定性被考虑在内时，所有样品基本上都属于钻石与含 CO2 熔体共存的稳定场。所以，