COLLABORATIVE RESEARCH: Thermochronologic Closure Temperature in Regional Metamorphic Settings: An Empirical Study

合作研究：区域变质环境中的热年代学闭合温度：一项实证研究

• 批准号: 9304072
• 负责人: Kip Hodges
• 金额: $ 22.32万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1993
• 资助国家: 美国
• 起止时间: 1993-08-01 至 1998-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9304072&HistoricalAwards=false
• 关键词: COLLABORATIVE; RESEARCH; Thermochronologic; Closure; Temperature

9304072 Hodges Rigorous inversion of petrologic and geochronologic data to estimate parameters such as unroofing rate in ancient orogenic belts requires precise estimates of pressure-temperature and time-temperature paths for a variety of structural levels. Uncertainties in Tt paths largely stem from uncertainties in the temperatures at which isotopic themochronometers become closed with respect to loss of radiogenic daughter nuclides. Factors that can result in variable closure temperatures for a given mineral- isotopic system include: 1) compositional differences; 2) the extent of interaction with infiltrating fluids; and 3) differences in the effective diffusion dimension for the radiogenic daughter due to reaction or deformational history. The relative importance of these factors or deformational history. The relative importance of these factors in governing closure behavior is not well understood for most commonly used thermochronometers. This project is intended to improve this situation through a systematic empirical study of thermochronometers based on the U-Pb and K-Ar (40Ar/39Ar) decay schemes in the Connemara region or Ireland. Connemara was chosen for this study because it provides an unparalleled opportunity to race a variety of lithologies, containing many thermochronometrically important minerals, continuously from garnet grade to second sillimanite grade. We intend to explore variations in mineral ages as a function of composition, microstructure, grain size, and metamorphic grade. An important component of this work will be the coupling of thermochronology with detailed stable isotopic work in an effort to evaluate the significance of fluids in the radiogenic isotopic evolution of thermochronologic systems. The research will improve our understanding of the geochemical behavior of these systems, as well as provide important insights into the reliability of assumptions commonly used in the construction and interpretation of time- temperature paths in orogenic settings.

9304072霍奇斯对岩石学和地质年代学数据进行严格的反演，以估计古造山带的去顶速率等参数，需要精确估计各种构造层次的压力-温度和时间-温度路径。TT路径的不确定性在很大程度上源于同位素测温计时因放射性核素损失而关闭的温度的不确定性。可能导致特定矿物-同位素系统封闭温度不同的因素包括：1)成分差异；2)与渗透流体相互作用的程度；以及3)由于反应或变形历史导致的放射性成因子体的有效扩散维度的差异。这些因素或变形历史的相对重要性。对于最常用的温度计时器来说，这些因素在控制关闭行为中的相对重要性还没有得到很好的理解。该项目旨在通过在康涅马拉地区或爱尔兰对基于U-Pb和K-Ar(40Ar/39Ar)衰变方案的温度计时器进行系统的经验研究来改善这一情况。康奈马拉之所以被选中进行这项研究，是因为它提供了一个无与伦比的机会来测试各种岩性，其中包含从石榴石等级到第二级硅线石等级的许多具有热学意义的重要矿物。我们打算探索矿物年龄随成分、显微结构、颗粒大小和变质程度的变化。这项工作的一个重要组成部分将是将热年代学与详细的稳定同位素工作结合起来，以努力评价流体在热年代学系统的放射性成因同位素演化中的意义。这项研究将提高我们对这些系统的地球化学行为的理解，并对造山带环境中时间-温度路径的构建和解释中常用的假设的可靠性提供重要的见解。