Collaborative Research: Tectonic Rates From Garnet Differential Geochronology

合作研究：石榴石差异地质年代学的构造速率

• 批准号: 0810167
• 负责人: Frank Spear
• 金额: $ 0.95万
• 依托单位: Rensselaer Polytechnic Institute
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-15 至 2010-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0810167&HistoricalAwards=false
• 关键词: Collaborative; Research; Tectonic; Rates; Garnet

Summary: Collaborative research: Tectonic rates from garnet differential geochronology Funding is requested to investigate rates of garnet growth and P-T changes through Sr isotope differential geochronology. The last two decades have witnessed rapid growth in analytical capabilities for measuring Sr isotopes in minerals, such that compositional changes can be resolved with a spatial resolution almost an order of magnitude better than 20 years ago, and rates of garnet growth can be measured more efficiently. Rates of garnet growth and P-T changes through differential Sr isotope analysis will be characterized in metamorphic suites from three regions. Intellectual Merit. The proposed research addresses two basic questions regarding mineral growth and metamorphism: (1) How fast do garnets grow in regional metamorphic settings? (2) Are regional metamorphism and tectonism punctuated and brief, or gradual and prolonged? Samples will include 3 classic settings: the nappe pile of central New England, HP/UHP rocks of the Alpine-Cyclades belt, and Barrovian rocks of Cordillera Darwin (southernmost Chile). Garnet growth rates will be measured in 10 samples total that are most representative of their respective terranes and metamorphic evolution. Geochemical characterization, and petrologic and tectonic interpretations have already been published for these rocks, vastly simplifying the proposed research. Most samples have experienced closed-system behavior with respect to fluid exchange with adjacent lithologies. Specific grains in each rock will be screened using X-ray maps (electron microprobe, RPI) and trace element profiles (LA-ICP-MS, WSU) to ensure that zoning patterns conform with published data. Microsamples ( 1mm) of garnets will be analyzed for Rb/Sr and 87Sr/86Sr ratios. Differential geochronology will establish how long each garnet took to grow, and used to test tectonic models based on each rock's P-T path. These data will test the validity of the recent proposal that garnet growth in Barrovian terranes is brief (1 Myr) and associated with distinct thermal pulses, viz a viz classic models of garnet growth in response to tectonically-induced thermal perturbations, which imply that garnets grow over Myrs to 10s of Myrs. Broader Impacts. This work will support the education of a graduate student in geochemistry, petrology, and geochronology. Also, the PIs publish and present results in a timely and appropriate fashion to other geoscientists, so results will become rapidly available to the scientific community.

摘要：协作研究：需要用SR同位素差异学通过SR同位素差异学调查石榴石差异地年代学资金的构造率。过去二十年来，分析能力的快速增长，用于测量矿物质中的SR同位素，因此可以通过空间分辨率更好地解决成分变化，几乎比20年前更好的数量级，并且可以更有效地测量石榴石生长的速率。通过差异SR同位素分析，石榴石生长和P-T变化的发生率将在三个区域的变质套件中表征。智力优点。拟议的研究解决了有关矿物生长和变质的两个基本问题：（1）石榴石在区域变质的环境中生长的速度？ （2）区域变质和构造构成构造，短暂，逐渐延长？样品将包括3种经典设置：新英格兰中部的纳普堆，高山骑行带的HP/UHP岩石以及Cordillera Darwin的Barrovian Rocks（最南端的辣椒）。石榴石生长速率将在10个样本中测量，这些样本总数最能代表其各自的地层和变质的进化。地球化学特征以及岩石学和构造解释已经为这些岩石发表，大大简化了所提出的研究。大多数样品在与相邻岩性的流体交换方面经历了封闭系统的行为。将使用X射线映射（电子微探针，RPI）和跟踪元素轮廓（LA-ICP-MS，WSU）筛选每个岩石中的特定晶粒，以确保分区模式符合已发布的数据。将分析RB/SR和87SR/86SR比的微型样本（1mm）石榴石。差异地年代学将确定每个石榴石要生长多长时间，并用于基于每个岩石的P-T路径测试构造模型。这些数据将测试最近提出的提议的有效性，即Barrovian Terranes的石榴石生长是简短的（1 Myr），并且与不同的热脉冲有关，即一种响应于构造诱导的热扰动的石榴石生长的经典模型，这暗示着石榴石在Myrs to Myrs的10s中生长。更广泛的影响。这项工作将支持对地球化学，岩石学和年代学研究生的教育。此外，PIS发布和介绍的结果及时，适合其他地球科学家，因此结果将迅速为科学界获得。