Structure-Based Thermodynamic Properties of Feldspars

长石矿物占地壳的60%。因此，了解它们的热力学和弹性性质对于理解从微观到造山尺度的所有尺度上的岩石学和地球化学过程至关重要。在之前NSF-EAR基金的支持下，我们的研究小组已经确定了一组长石矿物斜长石的弹性特性，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。另外一半是碱长石（NaAlSi3O8 ~ KAlSi3O8），其状态方程和弹性数据很少。现存的少量数据大多是陈旧的、相互矛盾的，没有显示出成分或结构状态的明确趋势。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，结合我们之前研究中开发的晶体化学概念，将使我们能够建立第一个基于结构的长石热力学模型，该模型将把长石的体积固溶体和稀释（微量元素）体系的描述统一为一个单一的、一致的描述。所得到的模型将预测阳离子位置大小和框架结构作为压力、温度和阳离子含量的函数。反过来，这将允许弹性，热膨胀和混合体积的计算在任何压力，温度和成分。该模型的成功开发不仅可以预测长石的热力学性质，还可以为控制长石、熔体和流体之间阳离子分配的原子尺度机制提供见解，以及地震波速度和地壳各向异性的关键制约因素。因此，这样一个模型将对广泛的地球科学家，包括矿物学家、岩石学家、地球化学家和地球物理学家都有很大的用处和兴趣。我们正在发展的用来描述长石对P、T和X的反应的晶体化学原理应该同样适用于其他框架矿物，包括工业上重要的沸石矿物和技术上重要的钙钛矿。

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.