Collaborative Research: Developing a Practical and Quantitative Method for Measurement of Metamorphic Porphyroblast Crystallization Kinetics and Strain Rate

“该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。“这个项目是西华盛顿大学、亚拉巴马大学塔斯卡卢萨分校和波士顿大学的研究人员之间的合作，重点是提高我们对岩石在地壳深处被加热、加压和变形时会发生什么的理解，这是一个每天都在我们脚下发生的过程（变质作用）。研究人员努力了解岩石变形的速率以及变质过程中新晶体生长的速率。人们对变质作用的这些基本参数知之甚少。研究人员将开发和测试一种新的方法，用于确定来自佛蒙特州汤森大坝的岩石的这些速率，这些岩石在大约3.8亿年前北美和东部微大陆之间的碰撞中变质。该研究将估计这次碰撞（以及其他类似的碰撞事件）期间变质和变形的速率，但更重要的是，该项目将开发一种新方法，通过这种方法，未来其他研究人员可以在其他地区研究变质作用的这些和相关方面。调查将集中在石榴石，一种常见的变质矿物，往往记录其生长环境的细节。这项研究依赖于最近在小体积石榴石的Sm-Nd放射性测年方面的进展。研究人员将确定岩石中石榴石晶体的特征部分的日期，以将石榴石化学与石榴石生长时间联系起来。该方法的关键是，它将允许许多间接日期很容易地获得参考辛苦获得的时间-化学联系。正在研究的具体问题是：什么是变质成核率，它们如何随时间变化？单个晶体的生长速率是什么？它们在晶体生长过程中是如何变化的？在大陆碰撞过程中，岩石变形的速度有多快？这种变形是连续的还是偶发的？在碰撞过程中，岩石加热和加载的速度有多快？最后，这项研究将提供第一个数据集，对成核和生长的理论模型可以进行测试。

"This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5)." This project, which is a collaboration between researchers at Western Washington University, the University of Alabama at Tuscaloosa, and Boston University, is focused on improving our understanding of what happens when rocks are heated, pressurized, and deformed deep within the Earth's crust, a process (metamorphism) that is occurring every day under our feet. The researchers strive to understand the rates at which rocks are deformed and at which new crystals grow during metamorphism. These basic parameters of metamorphism are very poorly known. The researchers will develop and test a new method for determining these rates on rocks from Townshend Dam, VT, which were metamorphosed about 380 million years ago during a collision between North America and a micro-continent to the east. The study will estimate the rates of metamorphism and deformation during this collision (and by extension, other similar collision events), but more importantly, the project will develop a new method by which these and related aspects of metamorphism can be studied in other areas by other researchers in the future. The investigation will focus on garnet, a commonly formed metamorphic mineral that tends to record details of its environment as it grows. The research relies on recent advances in Sm-Nd radiometric dating of tiny volumes of garnet. The investigators will date well-characterized parts of garnet crystals in a rock to link the garnet chemistry to the time of garnet growth. The crux of the method is that it will allow numerous indirect dates to be easily obtained by reference to the arduously obtained time-chemistry link. The specific questions being studied are: What are metamorphic nucleation rates and how do they vary with time? What are growth rates for individual crystals and how do they vary over the course of a crystal's growth? How fast are rocks deformed during continental collisions, and is that deformation continuous or episodic? How fast are rocks heated and loaded during collisions? Finally, the study will provide the first data set of its kind, against which theoretical models of nucleation and growth can be tested.