Determination of Hydrogen Content of D/H Ratio of Nominally Anhydrous Minerals

在这个项目中，研究人员计划开发一种仪器，用于测量mg大小的名义无水矿物样品中含有的微量氢的丰度和同位素组成（D/H比），并将该方法应用于各种被认为对地球水收支很重要的地幔物质。预计该方法的准确度和精密度可与传统的从固体中真空提取氢相媲美，但适用于大约小1000到10000倍的样品。这项新技术是对先前技术的改进，它将被设计用于提供名义上无水矿物中氢含量的绝对测量。目前存在几种测量矿物氢含量相对差异的方法，其中两种（FTIR和SIMS）比研究人员将开发的测量方法更方便和/或具有更好的空间分辨率。然而，FTIR和SIMS依赖于已知含水量的参考物质。这种材料的稀缺是这一领域的主要限制。这项新技术一旦开发出来，将用于扩大作为研究名义上无水矿物基础的一套实验室间标准。通过对氢丰度和同位素组成的耦合测量，pi将能够进行同位素标记实验，清楚地区分表面和溶解（可能还有其他）对分析样品总含水量的贡献。他们还将调查以前没有用FTIR或其他方法（主要是由于缺乏标准）研究过的矿物的含水量。该实验室对小样本进行氢同位素分析的初步工作表明，有可能极大地提高我们对名义上无水地幔矿物的D/H比的认识，从而限制这些矿物作为地球水收支水库的作用。这项研究的一些主要的更广泛的影响将是加强可传递给社区的氢同位素分析的分析基础设施，以及对地球化学领域的学生进行教育和培训。

EilerEAR-0337796In this project, the investigators plan to develop an apparatus for measuring the abundance and isotopic composition (D/H ratio) of trace hydrogen contained in mg-sized samples of nominally anhydrous minerals, and apply that method to various mantle materials that are believed to be important to the Earth's water budget. It is expected that this method will have accuracy and precision comparable to conventional vacuum extraction of hydrogen from solids, but will be applicable to samples approximately 1000 to 10,000 times smaller. This new technique is an improvement over previous ones and it will be designed to provide absolute measurements of the amounts of hydrogen in nominally anhydrous minerals. Several methods exist for measurements of relative differences in hydrogen content of minerals, and two of these (FTIR and SIMS) are more convenient and/or have better spatial resolution than the measurement the investigators will develop. However, FTIR and SIMS are dependent on reference materials having known water contents. The scarcity of such materials is a major limitation to this field. This new technique, once developed, will be used to expand the suite of inter-laboratory standards that are the foundation of studies of nominally anhydrous minerals. By coupling measurements of H abundance and isotopic composition, the PIs will be able to conduct isotopic labeling experiments that clearly separate surface and dissolved (and perhaps other) contributions to total water contents of analyzed samples. They will also survey the water contents of mineral species that have not been previously studied by FTIR or other methods (principally due to the lack of standards). Preliminary work with hydrogen isotope analyses of small samples by this laboratory indicates that it is possible to dramatically improve our knowledge of the D/H ratios of nominally anhydrous mantle minerals, and thereby constrain the role of such minerals as reservoirs for the Earth's water budget. Some of the main broader impacts of this research will be in the enhancement of analytical infrastructure for hydrogen isotope analyses that could be passed to the community, and in the education and training of students in the field of geochemistry.