Thermodynamics of Aluminous Amphiboles

该项目将把pi关于无铝“四边形”角闪石的晶体学和热力学性质的工作扩展到含铝正交晶长石系列和单斜角闪石系列，这两种类型都广泛存在于结晶岩石中。在700 -1000℃和高压下平衡前后，将对包含Mg/Fe比和al含量范围的天然样品进行x射线单晶结构改进。位点散射和键长数据将与成分数据相结合，以提供八面体和四面体位点有序-无序作为温度函数的描述。这些复杂角闪石的吉布斯能被明确地写为包括测量的构型熵，以及端元，互反和互序项。实验、热化学和自然相平衡数据提供了额外的约束。这些数据允许计算岩浆和亚固体系统的相图，包括角闪石和其他矿物，这些系统以前已经建立了一致的热力学模型。

9706326 Evans This project will extend the PIs work on the crystallographic and thermodynamic properties of the aluminum-free "quadrilateral" amphiboles into the Al-bearing orthorhombic gedrite series and the monoclinic hornblende series, both of which occur widely in crystalline rocks. X-ray single crystal structure refinements will be done on suites of natural samples encompassing a range of Mg/Fe ratios and Al-contents, prior to and after equilibration at 700o-1000oC and high pressure. Site scattering and bond length data will be incorporated with compositional data to provide a description of octahedral and tetrahedral site order-disorder as a function of temperature. The Gibbs energy of these complex amphiboles is written to explicitly include the measured configurational entropy, as well as end-member, reciprocal and reciprocal-ordering terms. Experimental, thermochemical and natural phase equilibrium data provide additional constraints. These data allow calculation of phase diagrams for magmatic and subsolidus systems involving amphiboles and other minerals for which there are previously developed consistent thermodynamic models.