Phase Equilibria and Crystal-Chemistry of Some Calcic Amphiboles

9909452Jenkins定量使用角闪石来推导地壳变质作用或部分熔化过程中的压力、温度和氧逸度需要有关富含铁的角闪石的信息。 该提案将重点关注关键的富铁角闪石铁阳起石 (Ca2Fe5Si8O22(OH)2)，采用两种互补的方法：(1) 研究化学体系 CaO-FeO-SiO2-H2O 中的铁阳起石稳定性和化学性质，以及 (2) 研究富镁角闪石透闪石固溶体中的铁阳起石组分。 这项研究的一个具体目标是在已知的压力、温度和氧逸度下合成纯含铁角闪石。 这些角闪石将通过 X 射线衍射进行研究，以便使用 Rietveld 结构分析确定角闪石晶体结构中铁和镁的分布，并将通过穆斯堡尔光谱进行研究，以进一步表征阳离子分布并查看是否存在三价铁。 这些极细晶粒的合成角闪石的其他表征将包括分析透射电子显微镜，以获得单个晶粒的直接化学分析，并评估其晶体结构中存在的缺陷数量（如果有）。 通过这项研究，我们将获得对端元铁阳起石热力学性质的重要见解，检验三价铁可能大大提高其热稳定性的假设，并确定铁如何影响富镁角闪石的性质。 这项研究将为了解化学复杂的角闪石提供有价值的参考。

9909452JenkinsThe quantitative use of amphiboles for deducing the pressures, temperatures, and oxygen fugacities attending metamorphism or partial melting in the Earth's crust requires information on iron-rich amphiboles. This proposal will focus on the key iron-rich amphibole ferro-actinolite (Ca2Fe5Si8O22(OH)2) using two complementary approaches: (1) investigation of ferro-actinolite stability and chemistry in the chemical system CaO-FeO-SiO2-H2O, and (2) investigation of the ferro-actinolite component in solid solution with the magnesium-rich amphibole tremolite. One particular goal of this research is to synthesize pure iron-bearing amphiboles under known pressure, temperature, and oxygen fugacities. These amphiboles will be studied by X-ray diffraction for the purpose of determining the distribution of iron and magnesium in the crystal structure of amphibole using Rietveld structure analysis and will be studied by Mossbauer spectroscopy to further characterize the cation distribution and to see if ferric iron is present. Additional characterization of these extremely fine-grained synthetic amphiboles will include analytical transmission electron microscopy to obtain direct chemical analyses of individual grains and to assess the amount of defects, if any, that are present in their crystal structure. From this study we will gain important insights into the thermodynamic properties of the end-member ferro-actinolite, test the hypothesis that ferric iron may greatly increase its thermal stability, and determine how iron influences the properties of magnesium-rich amphiboles. This study will provide a valuable point of reference for understanding chemically complex amphiboles.