Oxidation States of Mantle Minerals

地幔矿物的氧化态

• 批准号: 9903735
• 负责人: Peter Buseck
• 金额: $ 12.65万
• 依托单位: Arizona State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-09-01 至 2001-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9903735&HistoricalAwards=false
• 关键词: Oxidation; States; Mantle; Minerals

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.

9903735Buseck 地幔占地球质量和体积的最大部分。地幔内的地质过程深刻地影响着地球表面的主要特征（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地球物理测量或来自小型稀有样本。钻石和伴生矿物是这些样本中最突出的，是有关地幔信息的主要来源。一个重要的变量是它们的氧化态，但这很难确定。我们计划测量含铁地幔矿物（如石榴石、辉石和尖晶石）的氧化态，其中许多矿物以微小包裹体的形式出现在钻石中，以确定它们的铁/亚铁比率，然后我们将用该比率来计算地幔的氧化状态。我们将使用一种称为电子能量损失光谱 (EELS) 的基于电子束的分析技术进行测量。 EELS 使用透射电子显微镜完成，这意味着可以对极小的样品或样品区域进行测量，这在处理钻石中的内含物等情况时是一个主要优点。主要目标是通过使用一系列充分表征的地幔矿物，并将该技术与使用较粗晶体的其他方法的结果进行比较，来定义纳米尺度的 EELS 极限。结果将是更精确和准确的分析以及对地幔氧化态的新见解。