Collaborative Research: Tectonic Rates From Garnet Differential Geochronology

合作研究：要求从石榴石差异年代学资金中获得构造速率，以通过锶同位素差异年代学研究石榴石的生长速率和P-T变化。过去二十年见证了测量矿物中锶同位素的分析能力的快速增长，因此可以用比20年前高出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的生长速度。通过差示锶同位素分析，将表征三个地区变质岩套中石榴石的生长速率和P-T变化。智力上的功绩。这项研究解决了关于矿物生长和变质作用的两个基本问题：(1)区域变质背景下石榴石生长的速度有多快？(2)区域变质作用和构造作用是断续和短暂的，还是渐进和长期的？样品将包括3个经典背景：新英格兰中部的推覆体堆，阿尔卑斯山-旋回带的HP/UHP岩石，以及科迪勒拉达尔文(智利最南端)的巴罗维亚岩石。石榴石的生长速率将在10个样品中进行测量，这些样品最能代表各自的地体和变质演化。这些岩石的地球化学特征、岩石学和构造解释已经发表，极大地简化了拟议的研究。大多数样品都经历了与相邻岩性的流体交换的闭合系统行为。将使用X射线图(电子微探头，RPI)和微量元素分布图(LA-ICPMS，WSU)对每块岩石中的特定颗粒进行筛选，以确保分带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87Sr/86Sr比值的分析。差异年代学将确定每一块石榴石生长所需的时间，并用于测试基于每块岩石的P-T轨迹的构造模型。这些数据将检验最近提出的巴罗纪地体中石榴石的生长是短暂的(1 Myr)并与不同的热脉冲有关的观点的有效性，即石榴石生长的经典模型对构造诱导的热扰动的响应，这意味着石榴石在Myir到10 Myr之间生长。更广泛的影响。这项工作将支持研究生在地球化学、岩石学和地质年代学方面的教育。此外，私人投资机构以及时和适当的方式向其他地球科学家公布和展示结果，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.