Structure-Based Thermodynamic Properties of Feldspars

长石基于结构的热力学性质

• 批准号: 1118691
• 负责人: Nancy Ross
• 金额: $ 39.83万
• 依托单位: Virginia Polytechnic Institute and State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-08-01 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1118691&HistoricalAwards=false
• 关键词: Structure; Based; Thermodynamic; Properties; Feldspars

Feldspar minerals comprise 60% of the Earth's crust. Therefore knowledge of their thermodynamic and elastic properties is essential for understanding petrological and geochemical processes at all scales from the microscopic to the scales of mountain building. With the support of a previous NSF-EAR grant, our research group has determined the elastic properties of one group of the feldspar minerals, the plagioclase feldspars, whose compositions range from NaAlSi3O8 to CaAl2Si2O8. These plagioclase feldspars comprise about half of the feldspars found in the Earth's crust. The other half are the alkali feldspars (NaAlSi3O8 to KAlSi3O8), for which there is very little equation of state or elasticity data. What little data that does exist is mostly old, contradictory, and exhibits no clear trends with either composition or structural state. We will to address this critical gap in our knowledge base by determining high-precision equation of state and structural data on alkali and ternary feldspars. This new data, combined with the crystal-chemical concepts developed in our previous research, will allow us to build the first structure-based thermodynamic model for feldspars that will unite the description of their bulk solid solutions and that of their dilute (trace element) regimes into a single, consistent description. The resulting model will predict cation site sizes and framework configuration as a function of pressure, temperature and cation content. This in turn will allow elasticity, thermal expansion and the volumes of mixing to be calculated for any pressure, temperature and composition. The successful development of this model will not only allow thermodynamic properties of feldspars to be predicted, but will also provide insights in to the atomic-scale mechanisms that control cation partitioning between feldspars, melts and fluids, and key constraints on seismic wave velocities and anisotropy in the Earth's crust. Such a model will therefore be of great use and interest to a broad range of earth scientists, including mineralogists, petrologists, geochemists and geophysicists alike. The crystal-chemical principles that we are developing to describe the response of feldspars to P,T, and X should be equally applicable to other framework minerals, including the industrially important zeolite minerals and technologically important perovskites.

长石矿物占地壳的 60%。因此，了解它们的热力学和弹性特性对于理解从微观到造山尺度的所有尺度的岩石学和地球化学过程至关重要。在之前 NSF-EAR 资助的支持下，我们的研究小组确定了一组长石矿物的弹性特性，即斜长石，其成分范围从 NaAlSi3O8 到 CaAl2Si2O8。这些斜长石约占地壳中发现的长石的一半。另一半是碱长石（NaAlSi3O8 至 KAlSi3O8），其状态方程或弹性数据很少。确实存在的少量数据大多是旧的、矛盾的，并且在成分或结构状态方面没有表现出明显的趋势。我们将通过确定碱长石和三元长石的高精度状态方程和结构数据来解决我们知识库中的这一关键空白。这些新数据与我们之前研究中开发的晶体化学概念相结合，将使我们能够建立第一个基于结构的长石热力学模型，该模型将统一对其本体固溶体和稀释（微量元素）的描述制度转化为单一、一致的描述。所得模型将预测阳离子位点大小和框架构型作为压力、温度和阳离子含量的函数。这反过来将允许计算任何压力、温度和成分的弹性、热膨胀和混合体积。该模型的成功开发不仅可以预测长石的热力学性质，而且还可以深入了解控制长石、熔体和流体之间的阳离子分配的原子尺度机制，以及地震波速度和各向异性的关键约束在地壳中。因此，这样的模型对于包括矿物学家、岩石学家、地球化学家和地球物理学家等在内的广泛地球科学家来说将具有很大的用途和兴趣。我们正在开发的用于描述长石对 P、T 和 X 响应的晶体化学原理应该同样适用于其他骨架矿物，包括工业上重要的沸石矿物和技术上重要的钙钛矿。