Diffusion-diffusive phase transformations in alkali feldspar

碱长石中的扩散-扩散相变

• 批准号: 429191048
• 负责人: Professor Dr. Sergiy Divinski
• 金额: --
• 依托单位: Fakultät für Physik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/429191048?language=en
• 关键词: Diffusion; diffusive; phase; transformations; alkali

Alkali feldspar, a binary solid-solution between albite (NaAlSi3O8) and K-feldspar (KAlSi3O8), pertains to the most abundant mineral group in the Earth’s crust. During changes in pressure and temperature it undergoes several phase transformations producing microstructures such as twinning, braid texture, or exsolution lamellas, which bear genetic information. At high temperatures alkali feldspar shows continuous miscibility. Below about 600°C a miscibility gap opens. During cooling from super-solvus temperatures, intermediate alkali feldspar exsolves forming an intergrowth of Na-rich and K-rich lamellas, known as perthite. With time, the lamellas undergo coarsening and increasing chemical separation, which are both time- and temperature dependent and have been calibrated for application in geo-speedometry.So far, the accuracy at which thermal histories can be reconstructed from perthites is limited, because calibration is largely based on exsolution experiments, which integrate over all underlying processes including Na-K diffusion, formation of new phase boundaries, and evolution of coherency stress. For an improved quantification of exsolution each of these processes must be calibrated independently, and their coupling must be understood. We will develop a model for Na-K-interdiffusion based on the determination of Na- and K tracer diffusion coefficients including temperature-, composition-, direction-, and strain-dependence using a novel tracer/interdiffusion technique. This will be complemented by ab-initio calculations of defect- and migration energies to be used in molecular dynamics and Monte Carlo simulations. Finally, exsolution experiments will be done and the nm scale exsolution lamellas will be analyzed using atom probe tomography. This will allow, for the first time, direct determination of the coherent solvus and of interdiffusion in strained alkali feldspar.The combination of the broad spectrum of theoretical, experimental and analytical methods make this project unique and will allow for substantial improvement of geo-speedometry applications based on diffusion and diffusive phase transformations in alkali feldspar. The consortium of researchers involved combines expertise in all relevant fields including the mineralogical insight and background in thermodynamics and diffusive phase transformations (R. Abart), in atomistic modeling (C. Dellago), diffusion theory, experimentation, and Monte Carlo simulation (S. Divinski).

碱长石是钠长石（NaAlSi 3 O 8）和钾长石（KAlSi 3 O 8）之间的二元固溶体，属于地壳中最丰富的矿物群。在压力和温度的变化过程中，它经历了几次相变，产生了诸如孪晶、辫状结构或出溶片层等微观结构，这些微观结构承载着遗传信息。在高温下，碱性长石显示出连续的可溶解性。低于约600°C时，可熔性间隙打开。在从超溶线温度冷却的过程中，中间碱性长石溶出形成富Na和富K薄片的共生体，称为条纹长石。迄今为止，从条纹长石中重建热历史的准确性有限，因为校正主要基于出溶实验，该实验综合了所有的基本过程，包括Na-K扩散、新相界的形成、以及相干应力的演化。为了改善出溶的定量，这些过程中的每一个都必须独立地进行校准，并且必须理解它们的耦合。我们将开发一个模型的基础上确定钠和钾示踪剂扩散系数，包括温度，成分，方向和应变依赖性，使用一种新的示踪剂/相互扩散技术的Na-K-相互扩散。这将是补充从头计算的缺陷和迁移能量用于分子动力学和蒙特卡罗模拟。最后，将进行出溶实验，并使用原子探针层析术分析纳米尺度的出溶片层。这将允许，第一次，直接测定的一致固溶线和相互扩散的应变碱长石。理论，实验和分析方法的广谱组合，使这个项目独特的，并将允许显着改善地质测速应用的基础上扩散和扩散相变碱长石。参与的研究人员联盟结合了所有相关领域的专业知识，包括矿物学的洞察力和热力学和扩散相变的背景（R。Abart），在原子建模（C. Dellago），扩散理论，实验和蒙特卡罗模拟（S。Divinski）。