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

这EaGER将支持初步的实验设计，以测试温度循环是否有显着的影响，在火成岩的晶体尺寸分布和晶体排列。这项研究的动机来自于观察到，在深成岩晶体尺寸的关系通常不匹配相平衡实验的预测，也没有晶体尺寸分布理论。例如，钾长石通常以巨大的晶体（10厘米长）出现，尽管它最后在花岗岩中与石英沿着共结晶。晶体尺寸关系表明，这些大晶体生长的同类相食较小的晶体。各种材料科学领域的实验（例如，食品加工）表明，如果温度场振荡，大晶体可以以牺牲小晶体为代价快速生长。初步研究将采用三重方法来研究温度循环对晶体大小关系的影响：（1）硫氰酸铵-氯化钴岩浆模拟系统中的实验;（2）在一个大气压气体混合炉中进行的天然镁铁质岩浆温度循环实验;（3）使用冷密封压力容器进行的花岗岩-水系统中的温度循环实验。将继续在岩浆模拟系统中进行实验，以开发关于晶体尺寸发展的定量数据集，并将在1个大气压和气体混合炉中进行实验，研究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将显著增加晶体生长速率的可能性，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，可以部分避免困扰高二氧化硅系统实验的动力学问题。这项工作的智力价值主要在于发展对控制晶体尺寸和晶体相互关系特性的过程的理解（即，结构）。结构是人们在野外很容易观察到的少数东西之一，通常是绘制深成岩地质图的基础，但最近的许多工作对深成岩结构的标准教科书解释提出了质疑。熔体存在系统中的振荡温度深刻地影响了许多材料的质地，这项研究将检验这样一种假设，即在变化的温度场中的结晶也对火成岩的质地产生了强烈的控制。特别是，晶体的大小和晶体排列，这两者都是至关重要的岩浆岩的火成岩和结构的解释，可能会受到强烈的温度振荡。这项工作的广泛影响是多方面的。这项工作将涉及岩石学、构造地质学、大地构造学和火山学等领域。如果深成岩中的晶体排列是由热梯度中的结晶作用引起的，那么用来理解岩浆侵位的特征（例如，晶体排列）必须重新评估。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促进新的微量分析技术的开发。预计该项目将为FSU的学生提供一条在北卡罗来纳州主校区工作和学习的途径。结晶过程的影片将在网上发布，用于课堂教学。该项目有很强的教育成分，有几篇本科论文和一个博士学位。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.