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

古代和现代沉积物中碎屑矿物的年代学记录可用于研究地球历史和构造变质作用。 在许多情况下，沉积物中的碎屑矿物是唯一保存下来的长期侵蚀山脉和大陆碎片的记录。 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，重要的是，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）地质年代学作为一个全新的窗口，进入地球？地质构造的过去。 石榴石的生长是为了响应岩石的变质作用，并记录了造山活动（通常与大陆碰撞有关）的形成部分，这些事件在目前可确定年代的碎屑矿物档案中可能完全被遗漏。 此外，通过分析石榴石颗粒的化学性质，可以将其年龄置于特定的压力-温度范围和其生长的构造背景（例如俯冲带，区域或接触变质）。 该项目的目标是探索，定义，并通过简化现有的分析和样品制备方法，在过去几年中开发的单颗粒碎屑石榴石年龄测定的应用，以推动可达到的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本进行测试，以及从三个不同的领域设置，每个都有自己的一套潜在的未来研究应用程序的研究碎屑矿物套件：1。太古代沉积物，如杰克山砾岩; 2。古生代造山砂岩侵蚀经典Barrovian型地点在苏格兰; 3。现代河流沉积物排水阿巴拉契亚山脉在北卡罗来纳州。通过开发和利用档案的古代碎屑石榴石年龄（及其矿物化学）有可能利用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组，以测试从其他碎屑矿物年龄人口得出的关于全球大陆增长速度的推断，并解决区域规模的问题，包括发病，进展，和episodicity的变质作用在整个造山活动。

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.