Stability and Thermochemistry of some Chlorine-bearing Calcium Amphiboles

富氯流体是基本地质过程中的重要因素，例如(I)在盐水中传输金属离子，(Ii)控制水化地壳岩石与密度较高的无水岩石(例如麻粒岩和榴辉岩)反应的地球温度和深度，以及(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床的形成，造山和板块构造的动力，以及火山喷发的风格。关于富氯流体如何与地壳岩石相互作用的细节知之甚少，从大洋地壳海水-岩石界面的近地表氯的并入，到中地壳到下地壳的卤水迁移。已知氯以重量百分比取代的最常见的造岩矿物之一是富含钙的角闪石。取代角闪石的氯量取决于周围盐水或熔体中的氯浓度以及宿主角闪石的化学成分。研究这种复杂的相互作用的一个起点是确定宿主角闪石中的哪些组成变量对其氯含量起最大的控制作用。这项建议的第一个目标是检查钾所起的作用，根据本实验室之前获得的结果，钾现在似乎在控制角闪石的氯含量方面极其重要。其次，将研究氯对这种通常含水矿物的上热稳定性的影响。第三，将确定一个或多个富氯闪石的基本热化学数据。对角闪石中氯的取代进行任何严格的分析，最终都需要给定的氯端元角闪石的基本热化学数据。获得这些目前根本不存在的数据，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，并欢迎代表人数不足的少数群体参加。还将为职前地球科学、化学、物理和小学教师提供培训机会。这项建议的研究将集中在以下三个主要目标上。首先，我们将考察几个关键的组成变量(亚铁含量、钾含量)对几种钙闪石中氯结合的影响。这将建立在宾厄姆顿大学已经完成的关于无钾钙闪石的研究基础上，这种闪石通常被发现氯含量非常有限。其次，富氯闪石的上热稳定性将通过相平衡方法进行测定，并与其富羟基的等价物的稳定性进行比较。目前还没有实验数据表明氯对角闪石的热稳定性的影响，因此这一信息将具有相当重要的意义。第三，热化学数据(体积、热容、生成热焓和第三定律熵)将通过直接测量和从相平衡数据推导相结合的方式获得。体积和热容的测量可以在宾厄姆顿大学进行，而生成焓则需要在加州大学戴维斯分校进行测量。第三定律的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氯在角闪石岩石和与其平衡的卤水之间的分配是基本的。这项研究的结果应该对那些在广泛的地质环境中工作的人感兴趣，这些地质环境包括海洋-岩石相互作用、地幔氯化物交代作用、地壳深部和上地幔变质作用以及成矿体和夕卡岩。

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.