Fluorine-Hydroxyl Diffusion in Fluorine-Bearing Rock-Forming Minerals

地壳内的许多地质事件都受到水和氟等挥发性成分的极大影响。大多数矿物不能结合这些挥发物，因此不能记录这些事件。然而，钛铁矿、角闪石和云母是含有少量羟基和氟的常见矿物。这些矿物可能保存有关在地质事件（如变质和火山爆发）期间存在的瞬时熔体和流体中挥发物浓度的信息。这项研究将经验评估这两种矿物的结合和保留的羟基和氟作为温度和压力的函数，从而提供有关矿物化学的基本信息，并产生一个工具，用于评估挥发物在地球的发展和现代地质过程中的性质。这项研究将具体应用所得到的数据，以两个地区复杂但明显不同的挥发性历史，塞里多褶皱带，巴西，和南俄克拉荷马州Aulacogen，美国。这项研究将主题的例子，每种矿物，钛铁矿，角闪石，黑云母，过量的氟或羟基的温度和压力相当于那些发现在地壳。这些成分通过扩散进入和离开矿物。过量组分的掺入在矿物的暴露表面处将是最大的，并且作为温度、压力和暴露时间的函数随着深度而减小。我们将主要使用粒子加速器技术表征这些组分的浓度分布作为深度的函数，并从该分布确定其扩散系数。每种成分的扩散率是每种矿物的基本属性，可用于评估天然样品中这些成分的浓度。就Serido褶皱带而言，预计该地区新元古代变质片岩内黑云母和角闪石中氟和羟基的扩散率将决定5.23亿年前变质和蚀变事件的影响。在南俄克拉荷马州的Aulacogen的情况下，在这5.4亿年的裂谷系统的发展过程中，在所有三种矿物的扩散率将是有用的限制氟和水的岩浆浓度。除了这两个领域之外，这项研究的数据无疑将应用于变质作用、深成岩作用、火山作用、矿床常见的热液蚀变事件等其他工作，而且很可能应用于材料科学中研究的合成结晶过程。

Many geologic events within the earth's crust are greatly influenced by volatile components such as water and fluorine. Most minerals cannot incorporate these volatiles, and therefore do not record these events. However, titanite, amphibole, and mica are common minerals that host small fractions of hydroxyl and fluorine. These minerals potentially preserve information about the concentrations of volatiles in the transient melts and fluids present during geologic events, like metamorphism and volcanic eruptions. This study will empirically evaluate both these minerals' incorporation and retention of hydroxyl and fluorine as a function of temperature and pressure, thus providing fundamental information about mineral chemistry and producing a tool for evaluating the nature of volatiles in the development of the earth and in modern geologic processes. The study will specifically apply the resulting data to two areas with complicated yet distinctly different volatile histories, the Serido Fold Belt, Brazil, and the Southern Oklahoma Aulacogen, USA.This study will subject examples of each mineral, titanite, pargasite amphibole, and biotite mica, to excess fluorine or hydroxyl at temperatures and pressures equivalent to those found in the earth's crust. These components move into and out of minerals by diffusion. The incorporation of the excess component will be greatest at the exposed surface of the mineral and decrease with depth as a function of temperature, pressure, and exposure time. We will characterize the concentration profile of these components as a function of depth, largely using particle accelerator techniques, and determine their diffusivities from this profile. The diffusivity of each component is a fundamental property of each mineral, useful in evaluating the concentration of these components in natural specimens. In the case of the Serido Fold Belt, it is anticipated that diffusivities of fluorine and hydroxyl in biotites and amphiboles within the region's Neoproterozoic metamorphic schists will determine the influence of the 523 million year old metamorphism and alteration events. In the case of the Southern Oklahoma Aulacogen, the diffusivities in all three minerals will be useful in constraining the magmatic concentration of fluorine and water during the development of this 540 million year old rift system. In addition to these two areas, the data from this study will undoubtedly find application in other work on metamorphism, plutonism, volcanism, the hydrothermal alteration events common to ore deposits, and quite possibly to synthetic crystallization processes studied in the material sciences.