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

地壳内的许多地质事件很大程度上受到水和氟等挥发性成分的影响。大多数矿物不能结合这些挥发物，因此不记录这些事件。然而，钛铁矿、角闪石和云母是常见的矿物，含有少量的羟基和氟。这些矿物潜在地保存了变质作用和火山喷发等地质事件中存在的瞬时熔体和流体中挥发物浓度的信息。这项研究将实证地评估这些矿物在温度和压力下对羟基和氟的结合和保留，从而提供关于矿物化学的基本信息，并产生一种工具，用于评估地球发展和现代地质过程中挥发性物质的性质。这项研究将把得出的数据具体应用于两个具有复杂但截然不同的挥发历史的地区--巴西的塞里多褶皱带和美国的南俄克拉荷马州奥拉克根。这项研究将使每种矿物--钛铁矿、闪石角闪石和黑云母--在与地壳中发现的温度和压力相同的温度和压力下暴露于过量的氟或羟基。这些成分通过扩散进入和流出矿物。过量组分在矿物裸露表面的掺入量最大，随着温度、压力和曝光时间的增加，随着深度的增加而减小。我们将主要使用粒子加速器技术，将这些组分的浓度分布表征为深度的函数，并根据该分布确定它们的扩散系数。每种成分的扩散系数是每种矿物的基本性质，在评估天然样品中这些成分的浓度时很有用。就Serido褶皱带而言，预计该地区新元古代变质片岩中黑云母和角闪岩中氟和羟基的扩散将决定5.23亿年前变质和蚀变事件的影响。就南俄克拉荷马凹陷而言，在这个5.4亿年前的裂谷系统的发展过程中，所有三种矿物中的扩散系数都将有助于限制岩浆中氟和水的浓度。除了这两个领域，这项研究的数据无疑将在变质作用、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中得到应用，并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.