Hydrogen Isotope Studies of Submarine Basalts

EilerEAR-0208127氢可以说是固体地球中最重要的次要元素：它控制着地幔岩石的熔融行为和流变学；它是地壳和地幔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度；它在硅酸盐熔体中的丰度强烈地影响着结晶分异。然而，与几乎任何其他元素(当然还有任何类似重要性的元素)相比，氢的地球化学描述得不那么好：对地球上氢的总丰度的合理估计跨越了近一个数量级的范围；主要地幔储集层中的氢的浓度、停留时间以及源和汇鲜为人知或只是猜测；我们相信，通过研究海底玄武岩的氢同位素组成(即D/H比)，可以促进我们对全球氢循环的理解，因为海底玄武岩的起源和演化受到地幔氢的影响。这类研究的潜力多年来已被认识到，但由于数据稀少，对没有表征其他重要地球化学参数的样品进行的同位素测量比例很大，以及缺乏实验室间的标准化，这一潜力尚未实现。我们建议表征与马里亚纳弧及其弧后盆地有关的海底玄武岩之间的D/H比变化，这是我们目前理解水在收敛边缘岩浆成因中作用的关键样本。我们将使用一种新的分析方法来测定少量(10‘S至数百微克)含水固体和玻璃的D/H比和H含量，其速度大约是常规分析的10倍，但具有类似的准确度和精密度。这种方法将使我们能够在合理的时间框架内产生相对较大、标准化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.