Mantle Oxidation States and the Solubility of Oxygen in Diamond

地幔流体的性质和碳质相(金刚石、石墨、碳酸盐、流体)的相对稳定性部分取决于氧化态。钻石对了解上地幔中氧逸度的变化特别感兴趣，因为虽然大多数钻石似乎是从地球上相对氧化的部分运来的，但有些钻石含有极少的矿物包裹体(例如，铁金属、碳硅石)。这些包裹体和含有它们的钻石记录的氧化状态必须与将它们带到地表的金伯利岩不同，并且在岩石成因上与金伯利岩无关。已公布的数据和一项中试实验表明，可测量的氧气在钻石中溶解。因此，在一定氧逸度范围内平衡的钻石可能含有不同量的氧气。这项调查的目的是：(A)确定氧在钻石中的溶解度；(B)确定钻石中的氧含量是否存在可用作氧逸度定性指标的系统性变化；以及(C)寻找钻石含氧量与包裹体组合、氮含量、同位素组成和位置等其他特征之间的关系。要讨论的问题包括：夹杂物减少的钻石含氧量是否少于没有夹杂物的钻石；碳硅铝石的出现有什么意义；只有在比认为地幔中存在的还原条件更严重的条件下才应该是稳定的矿物；氧逸度的变化是否在一定程度上控制了钻石氮含量和碳同位素组成的变化。氧气将在洛斯阿拉莫斯国家实验室进行分析。

The nature of mantle fluids and relative stabilities of carbonaceous phases (diamond, graphite, carbonate, fluid) are partly determined by oxidation state. Diamonds are of particular interest in understanding how oxygen fugacity varies in the upper mantle because while most appear to have been transported from relatively oxidized parts of the Earth, some contain extremely reduced mineral inclusions (e.g., iron metal, moissanite). These inclusions and the diamonds that contain them must record a different oxidation state than and be petrogenetically unrelated to the kimberlites that brought them to the surface. Published data and a pilot experiment indicate that measurable quantities of oxygen dissolve in diamond. Therefore, diamonds equilibrated under a range of oxygen fugacities may contain measurably different amounts of oxygen. The pints of this investigation are to: (a) determine the solubility of oxygen in diamond; (b) determine if there are systematic variations in diamond oxygen contents that can be used as qualitative indicators of oxygen fugacity; and (c) search for relationships between diamond oxygen contents and other characteristics, such as inclusion assemblages, nitrogen contents, isotopic compositions and localities. Among the questions to be addressed are, do diamonds with reduced inclusions contain less oxygen than those without such inclusions; what is the significance of the occurrences of moissanite, a mineral which should be stable only under much more reduced conditions than thought to exist in the mantle; might variations in oxygen fugacity in part control the variability in nitrogen contents and carbon isotopic compositions of diamonds. Oxygen will be analyzed at Los Alamos National Laboratory.