Collaborative Research: Tectonic Rates From Garnet Differential Geochronology

总结：合作研究：请求提供资金，通过锶同位素差异地质年代学研究石榴石生长速率和P-T变化。在过去的二十年里，测量矿物中Sr同位素的分析能力迅速增长，因此可以用比20年前好近一个数量级的空间分辨率来解决成分变化，并且可以更有效地测量石榴石生长速率。通过Sr同位素差示分析，研究了三个地区变质岩系中石榴子石的生长速率和P-T变化。智力优势。本研究提出了两个关于矿物生长和变质作用的基本问题：（1）石榴石在区域变质环境中的生长速度有多快？(2)区域变质作用和构造作用是间断的、短暂的，还是渐进的、长期的？样品将包括3个经典的设置：中央新英格兰的推覆体桩，阿尔卑斯-基克拉泽斯带的HP/UHP岩石，以及科迪勒拉达尔文（智利最南端）的Barrovian岩石。石榴石的生长速率将在10个样品中进行测量，这些样品最能代表其各自的石榴石和变质演化。这些岩石的地球化学特征、岩石学和构造学解释已经发表，大大简化了拟议的研究。大多数样品都经历了封闭系统的行为与相邻岩性的流体交换。将使用X射线图（电子探针，RPI）和微量元素剖面图（LA-ICP-MS，WSU）筛选每种岩石中的特定颗粒，以确保分区模式与公布的数据一致。将对石榴石的微量样品（1 mm）进行Rb/Sr和87 Sr/86 Sr比值分析。微分地质年代学将确定每个石榴石生长所需的时间，并用于测试基于每个岩石P-T路径的构造模型。这些数据将测试最近提出的Barrovian岩石中石榴石生长短暂（100万年）并与不同的热脉冲相关的建议的有效性，即石榴石生长响应于构造引起的热扰动的经典模型，这意味着石榴石的生长时间超过百万年到几十百万年。更广泛的影响。这项工作将支持地球化学，岩石学和地质年代学的研究生教育。此外，PI以及时和适当的方式向其他地球科学家发布和展示结果，因此结果将迅速提供给科学界。

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.