Stability and Thermochemistry of some Chlorine-bearing Calcium Amphiboles

富氯流体是基础地质过程中的重要介质，例如（i）在含水盐水中运输金属离子，（ii）控制地球中的温度和深度，其中水合地壳岩石与致密的无水岩石反应（例如，麻粒岩和榴辉岩），和（iii）控制与硅酸盐熔体共存的水相的性质。 这些地质作用分别控制着经济矿藏的形成、造山运动和板块构造的动力学以及火山爆发的类型。 富氯流体如何与地壳岩石相互作用的细节知之甚少，从海洋地壳中海水-岩石界面的氯近地表掺入到中地壳至下地壳水平的盐水迁移。 其中一种最常见的造岩矿物是富含钙的角闪石，已知氯在重量百分比水平上被取代。 替代角闪石的氯的量取决于环境盐水或熔体中氯的浓度以及主体角闪石的化学组成。 研究这种复杂的相互作用的一个出发点是确定在主机角闪石的成分变量施加最大的控制其氯含量。 该提案的第一个目标是研究钾的作用，根据本实验室先前获得的结果，钾在控制角闪石的氯含量方面似乎非常重要。 其次，氯对这种正常含水矿物的高温稳定性的影响将被研究。 第三，将确定一种或多种富氯角闪石的基本热化学数据。 任何严格的分析，氯取代成角闪石最终需要的基本热化学数据为给定的氯端元角闪石。 获得这些目前还不存在的数据将是对科学的重大贡献。 该提案为本科生和研究生提供了教育机会，并欢迎代表性不足的少数群体的参与。 此外，还将提供机会培训职前地球科学、化学、物理和小学教师。 首先，将检查几个关键的组成变量（亚铁含量，钾含量）上的氯纳入几个钙闪石的效果。 这将建立在宾厄姆顿大学已经对无钾钙闪石进行的研究的基础上，这些闪石通常被发现氯含量非常有限。 第二，富氯角闪石的高温稳定性将通过相平衡方法确定，并与其富羟基等价物的稳定性进行比较。 目前还没有实验数据证明氯对角闪石热稳定性的影响，因此这一信息将是相当重要的。 第三，热化学数据（体积、热容、生成焓和第三定律熵）将通过直接测量和从相平衡数据导出相结合来获得。 体积和热容的测量可以在宾厄姆顿大学进行，而生成焓的测量将需要在戴维斯的加州大学进行。 第三定律熵将从热稳定性边界导出。 科学文献中没有关于富氯角闪石的热化学数据，但这些信息对于严格处理含角闪石岩石和与之平衡的盐水之间的氯分配是至关重要的。 这项研究的结果应该是感兴趣的那些工作在广泛的地质背景，包括海洋岩石相互作用，地幔氯化物交代，地壳深部和上地幔变质，成矿体和矽卡岩。

Chlorine-rich fluids are important agents in basic geological processes such as (i) transporting metal ions in aqueous brines, (ii) controlling the temperatures and depths in the Earth where hydrated crustal rocks react to denser anhydrous rocks (e.g., granulites and eclogites), and (iii) controlling the nature of the aqueous phase coexisting with silicate melts. These geological processes control, respectively, the formation of economic mineral deposits, the dynamics of mountain building and plate tectonics, and the style of volcanic eruptions. The details of how chlorine-rich fluids interact with crustal rocks are poorly understood, ranging from the near-surface incorporation of chlorine at the seawater-to-rock interface in oceanic crust to the migration of brines in mid- to lower-crustal levels. One of the most common rock-forming minerals into which chlorine is known to substitute at weight-percent levels is calcium-rich amphibole. The amount of chlorine that substitutes into amphiboles depends on the concentration of chlorine in the ambient brine or melt as well as the chemical composition of the host amphibole. A starting point for examining this complex interplay is to determine what compositional variables in the host amphibole exert the greatest control on its chlorine content. The first goal in this proposal is to examine the role that potassium plays, which, based on prior results obtained in this lab, now appears to be extremely important in controlling the chlorine content of amphiboles. Second, the effect of chlorine on the upper-thermal stability of this normally hydrous mineral will be investigated. Third, basic thermochemical data for one or more chlorine-rich amphiboles will be determined. Any rigorous analysis of the substitution of chlorine into an amphibole ultimately requires the fundamental thermochemical data for a given chlorine end-member amphibole. Obtaining these data, which simply do not exist at this time, would be a major contribution to the sciences. This proposal provides educational opportunities for undergraduate and graduate students, and welcomes the participation of under-represented minorities. Opportunities will also be made available for the training of pre-service Earth Science, Chemistry, Physics, and elementary teachers.Research in this proposal will focus on the following three main goals. First, the effect of several key compositional variables (ferrous iron content, potassium content) on the incorporation of chlorine into several calcium amphiboles will be examined. This will build on research already done at Binghamton University on potassium-free calcium amphiboles which were generally found to have very limited chlorine contents. Second, the upper-thermal stability of chlorine-rich amphiboles will be determined by phase-equilibrium methods and compared to the stabilities of their hydroxyl-rich equivalents. At present there are no experimental data demonstrating the effect of chlorine on the thermal stability of an amphibole, so that this information will be of considerable importance. Third, thermochemical data (volume, heat capacity, enthalpy of formation, and third-law entropy) will be obtained by a combination of direct measurements and derivation from the phase-equilibria data. Volume and heat capacity measurements can be made at Binghamton University, while the enthalpy of formation will entail measurements at the University of California at Davis. The third-law entropy will be derived from the thermal stability boundary. Thermochemical data on chlorine-rich amphiboles are absent in the scientific literature, yet such information is fundamental to any rigorous treatment of the partitioning of chlorine between amphibole-bearing rocks and the brine with which it equilibrates. Results from this study should be of interest to those working in a wide range of geological settings, including ocean-rock interactions, mantle chloride metasomatism, deep crustal and upper-mantle metamorphism, and ore-forming bodies and skarns.