Solving real-world analytical challenges: Developing SIMS reference materials for quantifying hydrogen contents of orthopyroxene

氢，俗称水，是一种重要的微量物质，作为羟基基团掺入所谓名义上无水矿物的晶体结构中。地幔矿物如辉石和橄榄石中的水的存在对地幔的物理性质有很大的影响。因此，对地幔流变学的完整理解是基于对地幔中水的含量和分布的详细了解。因此，需要所有可能的地幔环境的定量数据，但这些数据几乎完全限于从次大陆地幔回收的样品。只有一个非常有限的数据集，由该提案的首席研究员和她的同事，存在亚大洋橄榄岩。这种明显的取样偏差可以直接归因于样品质量：次大陆捕虏体通常产生高质量的物质，而亚大洋和阿尔卑斯型地幔岩通常在性质上非常复杂。埃尔兰根小组已经成功地获得了第一个水数据的海洋橄榄岩使用红外（IR）光谱（是标准方法），但这一数据集仅限于相对较少的样本。由于强烈的断裂和蚀变，大多数这样的样品显示出差的晶体质量，有效地阻止了通过红外光谱的定量测量。这里提出的项目是为了克服固有的局限性，通过开发二次离子质谱法（西姆斯）作为一种替代方法，用于量化复杂的，细粒度的材料中的水含量的IR方法。我们的重点是斜方辉石，在过去已被证明是一个理想的代理散装地幔水。我们需要克服的关键挑战是，西姆斯需要一种可用于校准的基质匹配参考材料。因此，拟议中的研究的主要任务是确定天然orthopyroxenes，是非常适合的校准氢定量西姆斯。一旦确定和表征，所产生的一套参考材料将用于验证的原理西姆斯测量，将进行从海洋和高山型地幔标本回收的斜方辉石。

Hydrogen, colloquially water, is a significant trace substance that is incorporated as hydroxyl groups in the crystal structure of so-called nominally anhydrous minerals. The presence of water in Earth mantle minerals such as pyroxene and olivine has a disproportionally large effect on the physical properties of the Earth mantle. A complete understanding of mantle rheology is therefore based upon a detailed knowledge of the content and distribution of water within the mantle. Quantitative data from all possible mantle environments are therefore needed but such data are almost exclusively confined to samples recovered from the sub-continental mantle. Only a very modest data set, produced by this proposal's principal investigator and her co-workers, exists for sub-oceanic peridotites. This obvious sampling bias can be directly attributed to sample quality: Sub-continental xenoliths generally yield high-quality material, whereas sub-oceanic and alpine-type mantle rocks are often highly complex in nature. The Erlangen group has successfully obtained the first water data for oceanic peridotites using infrared (IR) spectroscopy (being the standard method), however this dataset is confined to a relatively small number of samples. The majority of such samples show poor crystal quality due to intense fracturing and alteration, effectively prohibiting quantitative measurements via IR spectroscopy. The project proposed here is intended to overcome the limitations inherent to the IR method by developing secondary ion mass spectrometry (SIMS) as an alternative approach for quantifying water contents in complex, fine grained materials. Our intended focus is on orthopyroxene, which in the past has proven to be an ideal proxy for bulk mantle water. The key challenge we will need to overcome it that SIMS requires that a matrix-matched reference material be available for calibration. Hence, the main task of the proposed study is to identify natural orthopyroxenes that are well-suited calibrants for hydrogen quantification by SIMS. Once identified and characterized, the resulting suite of reference materials will be used for proof-of-principle SIMS measurements that will be undertaken on orthopyroxene recovered from oceanic and alpine-type mantle specimens.