Fluorine in Nominally Anhydrous Minerals from the Upper Mantle

氟是大多数陆地岩浆的挥发性成分，影响：1）物理性质，2）微量元素迁移和流体的矿石沉积，以及3）火山排放的环境影响。F在岩浆中是比许多其他挥发物的近地表扰动的原生岩浆浓度，因此可能是一个最有用的代理陆上熔岩的挥发物含量。研究人员的初步工作表明，名义上的无水矿物（NAMs）可能是陆地F的主要矿物学宿主，这也是H的推断。此外，橄榄石巨晶的原始F含量似乎比H含量更忠实地记录。这些数据表明一个假设，即F系统地分配NAMs和可用于更好地了解不仅F的地幔地球化学，但也在天然地幔矿物中的H的行为。我们在这项工作中有四个主要目标：1）确定NAMs中F的丰度（包括橄榄石，石榴石和辉石）从上地幔的不同部分，2）以显示主元素和次元素（包括H）与NAMs中的F相关，以推断地幔过程中F的行为（俯冲相关的熔化和交代作用）和晶体化学对F掺入的控制，3）测量NAM和来自实验的骤冷液体之间的F分布以确定分配系数，以及4）在新的和现有的实验中测量氟的组成梯度以量化NAM中的扩散系数。该建议的一个重要部分是利用我们对样品历史的理解，在受控的岩石学背景下研究F分布。理想情况下，这项工作的结果将允许使用NAM中的微量氟含量来帮助确定形成含有它们的岩石的过程。

Fluorine is a volatile component of most terrestrial magmas that affects: 1) physical properties, 2) trace element transport and ore deposition by fluids, and 3) the environmental impact of volcanic emissions. F in magmas is less subject than many other volatiles to near-surface perturbation of primary magmatic concentrations, and may therefore be one of the most useful proxies for the volatile content of subaerial lavas. Preliminary work by the investigators suggests that nominally anhydrous minerals (NAMs) may be the principal mineralogical host for terrestrial F, as has also been inferred for H. Furthermore, the original F contents of olivine megacrysts appear to be more faithfully recorded than the H contents. These data suggest a hypothesis that F is systematically partitioned between NAMs and may be used to better understand not only F geochemistry of the mantle, but also the behavior of H in natural mantle minerals. We have 4 main objectives in this work: 1) to determine the abundance of F in NAMs (including olivine, garnet, and pyroxene) from different parts of the upper mantle, 2) to show how major and minor elements (including H) are correlated with F in NAMs in order to infer F behavior during mantle processes (subduction-related melting and metasomatism) and crystal-chemical controls on F incorporation, 3) to measure the distribution of F between NAMs and quenched liquids from experiments to determine partition coefficients, and 4) to measure the compositional gradients of fluorine in new and existing experiments to quantify diffusion coefficients in NAMs. An important part of this proposal is using our understanding of the history of samples to investigate F distribution in a controlled petrologic context. Ideally, the results of this work will be to allow the use of trace fluorine contents in NAMs to help determine the processes responsible for forming the rocks that contain them.