Abstract The Earth’s mantle holds more carbon than its oceans, atmosphere and continents combined, yet the distribution of carbon within the mantle remains uncertain. Our best constraints on the distribution of carbon within the upper mantle are derived from the carbon-trace element systematics of ultra-depleted glasses and melt inclusions from mid-ocean ridge basalts. However, carbon-trace element systematics are susceptible to modification by crustal processes, including concurrent degassing and mixing, and melt inclusion decrepitation. In this study we explore how the influence of these processes varies systematically with both the mantle source and melting process, thereby modulating both global and local carbon-trace element trends. We supplement the existing melt inclusion data from Iceland with four new datasets, significantly enhancing the spatial and geochemical coverage of melt inclusion datasets from the island. Within the combined Iceland dataset there is significant variation in melt inclusion C/Ba ratio, which is tightly correlated with trace element enrichment. The trends in C/Ba-Ba space displayed by our new data coincide with the same trends in data compiled from global ocean islands and mid-ocean ridges, forming a global array. The overall structure of the global C/Ba-Ba array is not a property of the source, instead it is controlled by CO2 vapour loss pre- and post-melt inclusion entrapment; i.e., the array is a consequence of degassing creating near-constant maximum melt-inclusion carbon contents over many orders of magnitude of Ba concentration. On Iceland, extremely high C/Ba ( > 100) and C/Nb ( > 1000) ratios are found in melt inclusions from the most depleted eruptions. The high C/Ba and C/Nb ratios are unlikely to be either analytical artefacts, or to be the product of extreme fractionation of the most incompatible elements during silicate melting. Whilst high C/Ba and C/Nb ratios could be generated by regassing of melt inclusions by CO2 vapour, or by mantle melting occurring in the presence of residual graphite, we suggest the high values most likely derive from an intrinsically high C/Ba and C/Nb mantle component that makes up a small fraction of the Icelandic mantle.

中文翻译：

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全球熔体包裹体 C/Ba 阵列：地幔变异、熔化过程还是脱气？

摘要 地幔中的碳含量比海洋、大气和大陆的总和还要多，但地幔内碳的分布仍不确定。我们对上地幔内碳分布的最佳限制来自于来自大洋中脊玄武岩的超贫化玻璃和熔体包裹体的碳微量元素系统。然而，碳微量元素系统易受地壳过程的影响，包括同时脱气和混合，以及熔体包裹体爆裂。在这项研究中，我们探讨了这些过程的影响如何随着地幔源和熔化过程而系统地变化，从而调节全球和局部碳痕量元素趋势。我们用四个新数据集补充了冰岛现有的熔体夹杂数据，显着提高了岛上熔体包裹体数据集的空间和地球化学覆盖率。在合并的冰岛数据集中，熔体夹杂物 C/Ba 比存在显着变化，这与微量元素富集密切相关。新数据显示的C/Ba-Ba空间趋势与全球海岛和洋中脊数据的趋势一致，形成全球阵列。全局 C/Ba-Ba 阵列的整体结构不是源的属性，而是受熔体前后夹杂物夹带的 CO2 蒸气损失控制；即，阵列是脱气的结果，在多个数量级的 Ba 浓度范围内产生近乎恒定的最大熔体夹杂碳含量。在冰岛，极高的 C/Ba ( > 100) 和 C/Nb ( > 1000) 比率存在于最耗竭喷发的熔体包裹体中。高 C/Ba 和 C/Nb 比不太可能是分析结果，也不太可能是硅酸盐熔化过程中最不相容元素极端分馏的产物。虽然高 C/Ba 和 C/Nb 比可以通过 CO2 蒸汽对熔体夹杂物的再气化产生，或者通过在残留石墨存在下发生的地幔熔化产生，但我们认为高值最有可能来自固有的高 C/Ba 和构成冰岛地幔的一小部分的 C/Nb 地幔成分。