Effect of Temperature Cycling on Crystal Size, Crystal Alignment, and Approach to Equilibrium in Magmas

地壳主要由喷发到地球表面的火山岩和未喷发的岩浆在地球内部结晶时形成的深成岩组成。解释这些岩石的一种方法是检查组成岩石的矿物的粒度分布。例如，许多火山岩含有少量的微小晶体，表明地球表面冷却迅速，而大多数花岗岩含有大晶体，表明深层冷却缓慢。这些基本关系早在一个多世纪前就已为人所知，并指导了我们对地壳的大部分了解，但最近的研究指出了这些解释中许多令人费解的不一致之处。特别是，许多花岗岩含有巨大的晶体(10厘米或更长)，它们一定是在岩石降温历史上生长得很晚的。这些晶粒度分布异常的根源可能在于温度的波动。初步实验表明，振荡温度可以在蚕食小晶体和促进大晶体生长方面发挥深远的作用。这一过程在材料科学的许多相关领域发挥着重要作用，包括食品技术、半导体、冶金以及地球和其他星球上的冰雪研究。这项研究将研究温度循环对岩浆中晶体大小和排列的影响。晶体大小关系表明，这些大晶体是通过蚕食较小晶体而生长的。计划采用四种方法研究温度循环对晶体尺寸关系的影响：(1)硫氰酸铵-氯化钴岩浆模拟体系实验；(2)单气氛气体混合炉中天然玄武岩和安山岩岩浆的温度循环实验；(3)使用冷封压力容器的花岗岩-水系统的温度循环实验；以及(4)活塞-圆筒装置中温度循环的初步研究。这些实验的目的是确定温度循环在火成岩结构演化中扮演的角色。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-atm和高压熔炉中进行实验，以检查不同温度对晶体生长的作用。这些实验的一个重要方面是，像在其他材料中看到的那样，振荡温度可能会显著提高晶体生长速度；如果是这样，那么困扰高硅系统实验的动力学问题可能会部分避免。

The Earth's crust is composed largely of volcanic rocks that were erupted onto the Earth's surface and plutonic rocks that formed when unerupted magma crystallized within the earth. One method by which these rocks are interpreted is to examine the size distribution of minerals that make up the rocks. For example, many volcanic rocks have contain small amounts of tiny crystals, indicating rapid cooling at the Earth's surface, whereas most granites contain large crystals that indicate slow cooling at depth. These basic relationships have been known for over a century and guide much of what we know about the Earth's crust, but recent work has pointed out many puzzling inconsistencies with these interpretations. In particular, many granites contain huge crystals (10 cm or more in length) that must have grown very late in the cooling history of the rock. The source of these anomalies in crystal size distribution may lie in temperature fluctuations. Preliminary experiments show that oscillating temperature can play a profound role in cannibalizing small crystals and promoting growth of large ones. This process plays an important role in many related fields of materials science, including food technology, semiconductors, metallurgy, and studies of snow and ice on the earth and other planets.This study will examine the effects of temperature cycling on crystal size and alignment in magmas. Crystal size relationships suggest that these large crystals grow by cannibalism of smaller crystals. It is planned to use a four-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 basaltic and andesitic magmas in a one-atmosphere gas-mixing furnace; (3) temperature cycling experiments in the granite-water system using cold-seal pressure vessels; and (4) pilot studies of temperature cycling in a piston-cylinder device. The goal of these experiments is to determine what role temperature cycling plays in the textural evolution of igneous rocks. 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 high-pressure 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, then the kinetic problems that plague experiments in high-silica systems may be partially avoided.