Detrital Garnet Sm/Nd Geochronology: A New Window into Earth's Tectonic Past

古今沉积物中碎屑矿物的年代学记录用于研究地球历史和构造变质过程。在许多情况下，沉积物中的碎屑矿物代表了长期被侵蚀的山脉和大陆碎片的唯一保存下来的记录。然而，现有的碎屑矿物地质年代学档案有重要的局限性，包括这些矿物直接约束构造（即造山和俯冲）过程的能力。该项目开创了使用碎屑石榴石钐钕（Sm-Nd）年代学作为研究地球的全新窗口的先河。S构造过去。石榴石的生长是对进阶变质作用的反应，记录了造山事件的形成部分（通常与大陆碰撞有关），而这在目前可确定年代的碎屑矿物档案中是完全遗漏的。此外，通过分析石榴石颗粒的化学成分，可以将其年龄置于特定的压力-温度范围和其生长的构造环境中（例如，俯冲带，区域或接触变质作用）。该项目的目标是通过简化过去几年开发的用于单粒碎屑石榴石年龄测年的现有分析和样品制备方法，探索、定义和突破样品大小和精度的限制。该方法将使用从新英格兰收集的样品以及从三个不同的野外环境中得到充分研究的碎屑矿物套件进行测试，每个都有自己的一套潜在的未来研究应用：太古宙沉积物，如杰克山砾岩；2. 苏格兰古生代造山带砂岩对经典巴罗维亚型的侵蚀3. 北卡罗莱纳州阿巴拉契亚山脉的现代河流沉积物。通过开发和利用古代石榴石碎屑年龄（及其矿物化学）的档案，有可能挖掘地球上最古老的构造变质过程的直接记录，探索造山事件的全球年龄群，以检验从其他碎屑矿物年龄群体中得出的关于全球大陆生长速度的推论，并解决涉及开始、进展、以及在造山过程中渐进性变质作用的偶发性。

The geochronologic record of detrital minerals in ancient and modern sediments is used to study Earth history and tectonometamorphic processes. In many cases, detrital minerals in sediments represent the only preserved record of long since eroded mountains and continental fragments. However, the available detrital mineral geochronologic archive has important limitations including, importantly, the ability for these minerals to directly constrain tectonic (i.e. mountain building and subduction) processes. This project pioneers the use of detrital garnet Samarium-Neodymium (Sm-Nd) geochronology as a brand new window into Earth?s tectonic past. Garnets grow in response to prograde metamorphism and record the formative portions of mountain building events (typically related to continental collision) that can be completely missed in the currently dateable detrital mineral archive. Furthermore, by analyzing the well-understood chemistry of a garnet grain, it is possible to place its age into a specific pressure-temperature range and tectonic context wherein it grew (e.g. subduction zone, regional, or contact metamorphism). The goal of this project is to explore, define, and push the limits on sample size and precision attainable by streamlining existing analytical and sample preparation methods developed over the past several years for application to single grain detrital garnet age dating. The method will be tested using samples collected from New England as well as well-studied detrital mineral suites from three diverse field settings, each with its own set of potential future research applications: 1. Archean sediments such as the Jack Hills conglomerate; 2. Paleozoic orogenic sandstones eroding the classic Barrovian type-locality in Scotland; 3. modern stream sediments draining the Appalachian Mountains in North Carolina.By developing and utilizing an archive of ancient detrital garnet ages (and their mineral chemistry) there is the potential to tap the very oldest direct record of tectonometamorphic processes on the planet, explore global age clusters of mountain building events to test inferences about the pace of global continental growth drawn from other detrital mineral age populations, and address regional scale questions involving the onset, progression, and episodicity of prograde metamorphism throughout a mountain building event.