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

碎屑石榴石 Sm/Nd 地质年代学：了解地球构造过去的新窗口

• 批准号: 1049350
• 负责人: Ethan Baxter
• 金额: $ 12.4万
• 依托单位: Trustees of Boston University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1049350&HistoricalAwards=false
• 关键词: Detrital; Garnet; Sm; Nd; Geochronology

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.

古代和现代沉积物中碎屑矿物质的测量记录用于研究地球历史和构造体形过程。 在许多情况下，沉积物中的碎屑矿物是自侵蚀山和大陆碎片以来唯一保存的记录。 但是，可用的碎屑矿物质档案档案具有重要的局限性，包括这些矿物直接限制构造（即山区建筑和俯冲）过程的能力。 该项目开创了使用碎屑石榴石samarium-neodymium（SM-ND）的使用，作为进入地球构造过去的全新窗口。 石榴石在响应进型变质的过程中生长，并记录山地建筑事件的形成部分（通常与大陆碰撞有关），这些部分在当前可数据的碎屑矿物档案中可能会完全遗漏。 此外，通过分析石榴石颗粒的化学理解，可以将其年龄置于特定的压力温度范围和构造环境中（例如俯冲带，区域或接触式变质）。 该项目的目的是通过简化过去几年中开发的现有的分析和样品制备方法来探索，定义和推动限制样本量以及可以实现的精确度，以应用于单粒碎屑石榴石年龄。 该方法将使用从新英格兰收集的样品以及从三种不同的野外环境中收集的样品以及经过良好的碎屑矿物套件进行测试，每套设置都有其自身的潜在未来研究应用程序：1。诸如杰克·山（Jack Hills）企业集团之类的Archean沉积物； 2。古生代造山学砂岩侵蚀了苏格兰经典的Barrovian型本地性； 3。现代溪流沉积物排干北卡罗来纳州的阿巴拉契亚山脉。通过发展和利用古代碎屑石榴石年龄的档案（及其矿物化学），有可能利用最古老的直接记录构成经济学过程的最古老的直接记录比例性问题涉及整个山区建筑事件的制图变质的发作，进步和发作性。