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。这个项目是由西华盛顿大学、阿拉巴马大学塔斯卡卢萨分校和波士顿大学的研究人员合作完成的，重点是提高我们对岩石在地壳深处加热、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在变质过程中的变形速度和新晶体的生长速度。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在佛蒙特州汤森德大坝的岩石上测定这些速率的新方法，这些岩石在大约3.8亿年前北美与东部一个微大陆的碰撞中发生了变质。这项研究将估计这次碰撞(以及其他类似碰撞事件)期间的变质和变形速率，但更重要的是，该项目将开发一种新的方法，以便将来其他研究人员可以在其他领域研究变质作用的这些方面和相关方面。调查的重点将是石榴石，这是一种常见的变质矿物，在生长过程中往往会记录其环境的细节。这项研究依赖于对少量石榴石进行Sm-ND辐射测年的最新进展。研究人员将对岩石中石榴石晶体的部分特征进行测年，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，它将允许通过参照艰苦获得的时间-化学联系轻松地获得大量间接数据。正在研究的具体问题是：变质成核速率是多少，它们是如何随时间变化的？单个晶体的生长速度是多少，它们在晶体生长过程中是如何变化的？岩石在大陆碰撞过程中变形的速度有多快？这种变形是连续的还是间歇性的？岩石在碰撞过程中加热和装载的速度有多快？最后，这项研究将提供此类研究的第一个数据集，可以用来检验成核和生长的理论模型。

"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.