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

“这项奖励是根据2009年美国复苏和再投资法案（公法111-5）资助的。”这个项目是由西华盛顿大学、塔斯卡卢萨阿拉巴马大学和波士顿大学的研究人员合作完成的，其重点是提高我们对地壳深处岩石被加热、加压和变形时发生的情况的理解，这一过程（变质作用）每天都在我们脚下发生。研究人员努力了解在变质作用期间岩石变形和新晶体生长的速率。人们对变质作用的这些基本参数知之甚少。研究人员将开发并测试一种新的方法，以确定来自弗吉尼亚州汤森德大坝的岩石的这些速率，这些岩石是在大约3.8亿年前北美洲与东部一个微大陆之间的碰撞中变质的。这项研究将估算这次碰撞（以及其他类似碰撞事件）期间变质作用和变形的速率，但更重要的是，该项目将开发一种新的方法，通过这种方法，其他研究人员可以在未来研究其他领域的变质作用和相关方面。调查将集中在石榴石上，石榴石是一种常见的变质矿物，在其生长过程中往往会记录下环境的细节。这项研究依赖于对小体积石榴石进行钐钕放射性测年的最新进展。研究人员将确定岩石中石榴石晶体特征明确的部分的年代，以将石榴石的化学成分与石榴石生长的时间联系起来。该方法的关键在于，它可以通过参考艰难获得的时间-化学联系，轻松地获得许多间接日期。正在研究的具体问题是：什么是变质成核速率，它们如何随时间变化？单个晶体的生长速率是多少？它们在晶体生长过程中是如何变化的？在大陆碰撞过程中，岩石的变形速度有多快？这种变形是连续的还是偶然的？岩石在碰撞过程中加热和加载的速度有多快？最后，这项研究将提供同类的第一个数据集，作为检验成核和生长理论模型的依据。

"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.