Investigation on Modulated Structures and Subsolidus Phase Relations of Intermediate Plagioclase Feldspars Using Integrated Experiment and Simulation Methods

斜长石斜晶石是地壳中最丰富的矿物。它们是许多商业花岗岩台面和地砖的主要矿物。 贵重的宝石，如透闪石、月光石和彩虹色的拉布拉多长石也是斜长石。自1940年首次发现以来，斜长石的晶体结构和形成机制一直是一个谜。该研究有助于地质学家定量地了解它们的结构、稳定性、形成机制和演化历史。研究结果将被纳入由调查人员教授的入门级和研究生级课程。研究团队致力于让不同的研究生和本科生参与他们的研究。调查人员和研究生将继续通过地质博物馆为K-12社区开展外联活动，通过夏季接触机会指导高中生，并开发用于学习的开源软件，如AtomTouch，这是一种用于教育目的的3D交互式移动的平台分子模拟软件工具。由于所研究的无公度调制在中间斜长石斜长晶石发生在一个广泛的组成范围内的连续变化，拟议的研究也将有利于在其他非常规（非周期性）晶体材料，如金属间化合物（3+1）D结构，可能成为未来应用的新材料的基础的无公度调制的研究。最近的像差校正的Z-对比成像结果从研究人员的小组揭示钙钠有序和非质心在富钠和富钙的e-斜长石长石。多学科团队将研究来自不同地质环境的中间斜长石斜晶石，这些斜长石斜晶石跨越整个成分范围（从~ An 25到~ An 75）。e-斜长石斜长晶石的结构改进将利用关于非中心性和超空间群特征的新突破来进行，以破译e-斜长石斜长晶石的复杂性质。该研究包括以下3个方面：（1）利用像差校正的扫描透射电子显微镜对中等斜长石的Z衬度成像;（2）利用单晶X射线衍射方法确定e-斜长石的晶体结构;（3）利用基于密度泛函理论的相图模型对斜长石二元体系的亚固相线相关系进行原子计算。中间斜长石的晶体结构和亚固相线相关系是矿物学和岩石学中非常基本和重要的课题。解决神秘的强烈调制构造及其亚固相线相关系问题，将有助于加深对经历不同演化历史的变质岩和火成岩中斜长石的行为及其共生/共生的认识。

Plagioclase feldspars are the most abundant minerals in the Earth's crust. They are major minerals in many commercial granite countertops and floor tiles. Precious stones like peristerite, moonstone, and iridescent labradorite are plagioclase feldspars too. The crystal structures and formation mechanisms of the plagioclase feldspars have been an enigma for decades beginning with their first discovery in 1940. The proposed study will help geologists to have quantitative understanding of their structures, stabilities, formation mechanisms, and evolution histories. The research results will be incorporated into both introductory level and graduate level courses taught by the investigators. The team of researchers is committed to the engagement of diverse graduate and undergraduate students in their research. The investigators and graduate students will continue outreach activities through the Geology Museum for K-12 community, mentoring high school students through summer reach opportunity, and developing open source software for learning, such as, AtomTouch, a 3D interactive mobile platform molecular simulation software tool for educational purposes. Because the studied incommensurate modulations in the intermediate plagioclase feldspars occur in a wide compositional range with continuous variation, the proposed study will also benefit the study of incommensurate modulations in other non-conventional (aperiodic) crystalline materials like intermetallic coumpounds with (3+1)D structures that may underlie new materials for future applications. Recent aberration-corrected Z-contrast imaging results from the investigator's group reveal Ca-Na ordering and non-centrosymmetricity in both Na-rich and Ca-rich e-plagioclase feldspars. The multidisciplinary team will investigate the intermediate plagioclase feldspars that span the entire composition range (from ~An25 to ~An75) from different geological environments. Structural refinements of e-plagioclase feldspars will be carried out using new breakthroughs regarding non-centrosymmetricity and super space group characteristics to decipher the intricate nature of e-plagioclase feldspars. The proposed study includes the following 3 tasks: (1) Z-contrast imaging of intermediate plagioclase feldspars using an aberration-corrected scanning transmission electron microscope; (2) Crystal structure determination of e-plagioclase feldspars by single crystal X-ray diffraction method; and (3) Atomistic calculation of the subsolidus phase relations of the plagioclase binary system using density functional theory based phase diagram modeling. Both crystal structure and subsolidus phase relation of the intermediate plagioclase feldspars are very basic and important topics in mineralogy and petrology. Solving the problems of the mysterious incommensurately modulated structures and their subsolidus phase relations will provide improved understanding about behaviors of the plagioclase feldpars and their associations / intergrowths in metamorphic and igneous rocks that have experienced different evolution histories.