Hydrogen Isotope Studies of Submarine Basalts

氢可以说是固体地球中最重要的微量元素：它支配着地幔岩石的熔融行为和流变；它是地壳和地幔中交代运输的主要溶剂；它在硅酸盐矿物中的浓度控制着其他元素的扩散速率；其在硅酸盐熔体中的丰度强烈影响结晶分异。然而，对氢的地球化学描述却不如其他任何元素（当然也不如同等重要的元素）：对地球上氢总丰度的合理估计跨越了几乎一个数量级的范围；主要地幔储层中氢的浓度、停留时间以及氢的来源和汇很少为人所知或只是猜测；而氢在矿物和熔体之间的分配还需要用研究其他微量元素的同样复杂的实验来描述。我们认为，通过研究具有良好特征的海底玄武岩套系的氢同位素组成（即D/H比值），可以促进我们对全球氢循环的理解，这些套系的起源和演化受地幔氢的影响。这种研究的潜力多年来一直被认识到，但由于数据稀疏，对样品进行的同位素测量中有很大一部分没有使用其他重要的地球化学参数进行表征，以及缺乏实验室间标准化，因此尚未实现。我们建议表征与马里亚纳弧及其弧后盆地相关的海底玄武岩的D/H比值变化，这是我们目前了解水在岩浆成因中的作用的关键样本。我们将使用一种新的分析方法来确定少量（10微克到数百微克）含水固体和玻璃的D/H比和H含量，其速度约为传统分析的10倍，但具有相似的准确性和精密度。这种方法将使我们在合理的时间框架内生成相对较大的、标准化的和复制良好的数据集。

EilerEAR-0208127Hydrogen is arguably the most important minor element in the solid earth: It dominates the melting behavior and rheology of mantle rocks; it is the principle solvent for metasomatic transport in the crust and mantle; its concentration in silicate minerals controls rates of diffusion of other elements; and its abundance in silicate melts strongly influences crystallization-differentiation. However, the geochemistry of hydrogen is less well described than that for virtually any other element (and certainly any of similar importance): Reasonable estimates of the total abundance of H in the earth span a range of nearly an order of magnitude; concentrations, residence times, and sources and sinks of hydrogen in major mantle reservoirs are poorly known or only guessed at; and partitioning of hydrogen between minerals and melts has yet to be described with the same experimental sophistication given to studies of other minor elements.We believe that our understanding of the global hydrogen cycle can be advanced by studying the hydrogen isotope composition (i.e., D/H ratio) of well characterized suites of submarine basalts whose origin and evolution is influenced by mantle hydrogen. The potential for such studies has been recognized for many years, but has not been realized due to sparse data, the large proportion of isotopic measurements on samples that are not characterized for other important geochemical parameters, and lack of inter-laboratory standardization. We propose to characterize the variation in D/H ratio among submarine basalts associated with the Mariana arc and its back arc basin, which are a key set of samples for our current understanding of the role of water in magma genesis at convergent margins. We will approach this study using a new analytical method for determining D/H ratios and H contents of small quantities (10's to hundreds of micrograms) of hydrous solids and glasses at a rate approximately 10x that of conventional analyses but with similar accuracy and precision. This method will let us produce relatively large, well standardized and well replicated data sets in a reasonable time frame.