Pilot Study: Effect of Temperature Cycling on Crystal Size and Alignment in Magmas

该 EaGER 将支持初步实验，旨在测试温度循环是否对火成岩中的晶体尺寸分布和晶体排列产生显着影响。这项研究的动机来自于观察到深成岩中的晶体尺寸关系通常与相平衡实验或晶体尺寸分布理论的预测不符。例如，钾长石通常出现在巨大的晶体（长度为 10 厘米）中，尽管它最后与石英一起在花岗岩中共结晶。晶体尺寸关系表明这些大晶体是通过较小晶体的同类相食而生长的。各种材料科学领域（例如食品加工）的实验表明，如果温度场振荡，大晶体会以牺牲较小晶体的速度快速生长。初步研究将采用三重方法来研究温度循环对晶体尺寸关系的影响：（1）硫氰酸铵-氯化钴岩浆模拟系统中的实验； (2)单一气氛混气炉中天然镁铁质岩浆的温度循环实验； (3)使用冷封压力容器进行花岗岩-水系统的温度循环实验。将继续在岩浆模拟系统中进行实验，以开发晶体尺寸发展的定量数据集，并在 1-atm 和气体混合炉中进行实验，以检查晶体生长温度变化的作用。这些实验的一个重要方面是振荡温度可能会显着提高晶体生长速率，正如在其他材料中所看到的那样；如果是这样，在未来的研究中可能会部分避免困扰高硅系统实验的动力学问题。这项工作的智力价值主要在于加深对控制深成岩晶体尺寸和晶体相互关系特征（即结构）的过程的理解。纹理是人们在野外可以轻松观察到的少数事物之一，并且通常是绘制深成岩地体地质图的基础，但最近的许多工作对教科书对深成纹理含义的标准解释提出了质疑。熔融存在系统中的振荡温度深刻地影响许多材料的质地，该研究将检验这样的假设：变化的温度场中的结晶也对火成岩的质地产生强有力的控制。特别是，晶体尺寸和晶体排列对于岩浆岩的火成岩和结构解释至关重要，可能会受到振荡温度的强烈影响。这项工作的更广泛影响是多方面的。这项工作将涉及岩石学、构造地质学、构造学和火山学领域。如果深成岩中的晶体排列可以由热梯度中的结晶产生，那么必须重新评估用于了解岩浆侵位的特征（例如晶体排列）。该项目可能为困扰高硅系统实验的令人烦恼的动力学问题提供部分解决方案，因为模拟实验表明，振荡温度会大大加速晶体生长。该项目将利用最近安装在费耶特维尔州立大学 (FSU) 的 JEOL Hyperprobe 促进微量分析新技术的开发。预计该项目将为佛罗里达州立大学的学生在北卡罗来纳大学主校区工作和学习提供一条途径。结晶过程的视频将发布在网上，用于课堂教学。该项目具有很强的教育意义，有几篇本科论文和一篇博士学位论文。论文计划。

This EaGER will support the preliminary experiments designed to test if temperature cycling has a marked effect on the crystal size distribution and crystal alignment in igneous rocks. The motivation for this study comes from the observation that crystal size relationships in plutonic rocks commonly do not match the predictions of phase equilibrium experiments nor of crystal-size distribution theory. For example, K-feldspar commonly occurs in huge crystals (10 cm in length) even though it co-crystallizes last in granites along with quartz. Crystal size relationships suggest that these large crystals grow by cannibalism of smaller crystals. Experiments in various materials science fields (e.g., food processing) show that large crystals can grow rapidly at the expense of smaller ones if the temperature field oscillates. The preliminary study will use a three-fold approach to studying the effects of temperature cycling on crystal size relationships: (1) experiments in the ammonium thiocyanate-cobalt chloride magma analog system; (2) temperature cycling experiments in natural mafic magmas in a one-atmosphere gas-mixing furnace; and (3) temperature cycling experiments in the granite-water system using cold-seal pressure vessels. Experiments in the magma analog system will be continued in order to develop a quantitative dataset on crystal size development, and experiments at 1-atm and in gas-mixing furnaces will examine the role of varying temperature of crystal growth. An important facet of these experiments is the possibility that oscillating temperature will dramatically increase crystal growth rates, as is seen in other materials; if so, kinetic problems that plague experiments in high-silica systems may be partially avoided in future studies.The intellectual merit of this work lies mainly in developing an understanding of the processes that govern the crystal size and crystal interrelationship characteristics (i.e., texture) of plutonic rocks. Texture is one of the few things one can easily observe in the field and is often the basis for drawing geologic maps in plutonic terranes, but much recent work casts doubt on the standard textbook interpretations of what plutonic texture means. Oscillating temperature in a melt-present system profoundly affects the texture of many materials, and the study will test the hypothesis that crystallization in a varying temperature field exerts a strong control on the texture of igneous rocks as well. In particular, crystal size and crystal alignment, both of which are critical to igneous and structural interpretation of magmatic rocks, may be strongly affected by oscillating temperature. The broader impacts of this work are many-fold. This work will bear on the fields of petrology, structural geology, tectonics, and volcanology. If crystal alignment in plutonic rocks can result from crystallization in a thermal gradient, then features used to understand magma emplacement (e.g., crystal alignment) must be reevaluated. The project may provide a partial solution to the vexing kinetic problems that plague experiments in high-silica systems, because analog experiments demonstrate that crystal growth is greatly accelerated by oscillating temperature. The project will facilitate the development of new techniques of microanalysis using the JEOL Hyperprobe that was recently been installed at Fayetteville State University (FSU). It is expected that the project will provide a pathway for students from FSU to work and study at the main campus of the University of North Carolina. Movies of crystallization processes will be posted online for use in classroom instruction. The project has a strong educational component, with several undergraduate theses as well as one Ph.D. thesis planned.