Oxidation States of Mantle Minerals

按质量和体积计算，地幔构成了地球的最大部分。地幔内的地质作用深刻地影响着地球表面的主要地貌(海洋盆地、山脉)。尽管地幔很重要，但所有关于地幔的知识都来自间接的地球物理测量或来自少量的稀有样品。钻石和伴生矿物是这些样品中最突出的，也是关于地幔的主要信息来源。一个重要的变量是它们的氧化状态，但这一点很难确定。我们计划测量石榴石、辉石和尖晶石等含铁地幔矿物的氧化状态，以确定它们的铁/铁比例，然后我们将利用这些比例来计算地幔的氧化状态。我们将使用一种基于电子束的分析技术，称为电子能量损失谱(EELS)进行测量。EELS是用透射电子显微镜完成的，这意味着可以对极小的样品或样品区域进行测量，这在处理钻石中的夹杂物时是一个主要好处。一个主要目标将是通过使用一系列特征良好的地幔矿物来定义鳗鱼在纳米尺度上的极限，并将这项技术与其他利用更粗晶体的方法的结果进行比较。结果将是更精确和准确的分析，以及对地幔氧化状态的新见解。

9903735Buseck The mantle comprises the largest fraction, by mass and by volume, of the Earth. Geologic processes within the mantle profoundly influence major features (ocean basins, mountains) at Earth's surface. In spite of its importance, all knowledge of the mantle is from indirect geophysical measurements or from small, rare samples. Diamonds and associated minerals are among the most prominent of these samples and are major source of information about the mantle. An important variable is their oxidation state, but this has been difficult to determine. We plan to measure the oxidation state of iron-bearing mantle minerals such as garnets, pyroxenes, and spinels, many of which occur as tiny inclusions within diamonds, in order to determine their ferric/ferrous ratios, which we will then use to calculate the oxidation state of the mantle. We will use an electron-beam-based analytical technique called electron energy-loss spectroscopy (EELS) for the measurements. EELS is done with a transmission electron microscope, which means measurements can be made on extremely small samples or regions of samples, a major benefit when dealing with, for example, inclusions in diamonds. A major goal will be defining the limits of EELS at the nanometer scale by using a series of well-characterized mantle minerals and comparing the technique to results from other methods that utilize coarser crystals. The results will be more precise and accurate analyses plus new insights into the oxidation state of the mantle.