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。大多数矿物质不能吸收这些挥发物，因此不记录这些事件。然而，钛矿、角闪洞和云母是常见的矿物质，含有少量的羟基和氟。这些矿物可能保存了地质事件（如变质作用和火山爆发）中瞬时熔体和流体中挥发物浓度的信息。这项研究将根据经验评价这些矿物的羟基和氟的结合和保留作为温度和压力的函数，从而提供关于矿物化学的基本信息，并为评价地球发展和现代地质过程中挥发物的性质提供工具。该研究将具体地将结果数据应用于两个具有复杂但明显不同的波动历史的地区，即巴西的塞里多褶皱带和美国的俄克拉何马州南部裂陷根。这项研究将对每种矿物（钛矿、闪石角闪洞和黑云母）在相当于地壳中发现的温度和压力下过量的氟或羟基进行实验。这些成分通过扩散进出矿物质。过量成分的掺入在矿物的暴露表面是最大的，随着温度、压力和暴露时间的变化，随着深度的增加而减少。我们将描述这些成分的浓度曲线作为深度的函数，主要使用粒子加速器技术，并从该曲线确定它们的扩散系数。每种成分的扩散率是每种矿物的基本性质，有助于评估这些成分在自然标本中的浓度。以塞里多褶皱带为例，预计该地区新元古代变质片岩内黑云母和角闪岩中氟和羟基的扩散率将决定5.23亿年变质和蚀变事件的影响。在南俄克拉荷马裂陷槽的情况下，这三种矿物的扩散率将有助于在这个5.4亿年历史的裂谷系统的发展过程中限制氟和水的岩浆浓度。除了这两个领域之外，本研究的数据无疑将应用于变质作用、深部作用、火山作用、矿床常见的热液蚀变事件，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.