Collaborative Research: Improving the Accuracy and Precision of Monazite and Allanite Geochronology via ID Th-Pb Ages for Reference Materials

从独居石和allanite中获得高精度、准确的基于标准的208Pb/232Th年龄的主要限制是缺乏合适的、表征良好的参考物质。由于独居石和allanite的成分都是可变的，而且SIMS， LA-ICP-MS会产生仪器质量依赖的分选，因此必须密切匹配未知的标准物。本文旨在确定富th副矿物独居石和allanite的同位素稀释（ID） Th-Pb年龄。目前只有一种常用的参考物质——“554”存在Th-Pb年龄。因此，所有基于标准的地质年代学测量都需要假设Th-Pb和U-Pb年龄是相等的。这种假设是不必要的，而且在许多情况下是无效的。通过获得一套特征良好的、广泛存在的参考物质的高精度ID Th-Pb年龄，本研究将为与基本构造过程相关的矿物提供一种独立校准Th-Pb年龄的方法。通过提供独立验证的U-Pb和Th-Pb年龄，消除了假设三个衰变系统（235U， 238u和232Th衰变链）之间一致性的需要。o提高了可直接与地质体变质和岩浆历史相联系的计时器的年龄测量精度，为高精度、基于标准的地质年代学提供了明确的标准。更广泛的impacts1。这项拟议的研究旨在解决EARTHTIME计划的基本目标：“发展地质年代学技术，以产生接近放射性同位素年龄0.1%的不确定性的时间约束。”o将开发一个网站，其中包含有关参考物质和测量ID TIMS和ICP-MS年龄的方法的信息。这些信息将被链接到地球时间网站。o将开发一个教育模块，该模块可集成到EARTHTIME任务中，用于教育学生了解地质时间。本模块将演示连接压力，温度和时间历史。该项目支持两位早期职业科学家——约翰·科特尔（UCSB教员）和艾米丽·彼得曼（斯坦福博士后）。此外，Peterman是一位年轻的女科学家（2009年博士学位）。这项研究将训练本科生（UCSB）进行实验室调查，并为UCSB和斯坦福大学的研究生提供研究生研究的一部分。所提出的研究结果将在很大程度上影响地球年代学界：o热电离质谱、二次电离质谱、电子探针微分析（激光烧蚀）、电感耦合等离子体质谱

Collaborative Research: Improving the accuracy and precision ofmonazite and allanite geochronology via ID Th-Pb ages for referencematerialsThe principal limitation for obtaining high-precision, accurate standard-based 208Pb/232Th ages from monazite and allanite is the lack of appropriate, well-characterized reference materials. Because both monazite and allanite are compositionally variable and SIMS, LA-ICP-MS incur instrumental mass-dependent fractionation, it is essential to closely match standards with unknowns. This proposal seeks to determine isotope dilution (ID) Th-Pb ages for the Th-rich accessory minerals monazite and allanite. Th-Pb ages currently exist for only one reference material that is commonly used-'554'. Consequently, all standard-based geochronologic measurements require an assumption that Th-Pb and U-Pb ages are equivalent. This assumption is unnecessary and, in many cases, invalid. By obtaining high-precision ID Th-Pb ages for a suite of well-characterized, community-wide reference materials, this research will provide a means of independently calibrating Th-Pb ages for minerals that can be linked to fundamental tectonic processes.Intellectual Merito Eliminates the need to assume concordance among the three decay systems (235U, 238Uand 232Th decay chains) by providing independently verified U-Pb and Th-Pb ages.o Improves precision on age measurements for a chronometer that can be directly linkedto the metamorphic and magmatic history of a terraneo Provides well-characterized standards to the community for high-precision, standardbasedgeochronology.Broader impacts1. This proposed research seeks to address the fundamental aim of the EARTHTIME initiative: "the development of the geochronological techniques necessary to produce temporal constraints with uncertainties approaching 0.1 % of the radioisotopic ages."o A website will be developed that contains the information about the reference materials and the methods for measuring the ID TIMS and ICP-MS ages. This information will be linked to the EARTHTIME website.o An educational module will be developed that can be integrated into the EARTHTIME mission for educating students about understanding geologic time. This module will demonstrate linking pressure, temperature and time histories.2. This project supports two early career scientists-John Cottle (UCSB faculty) and Emily Peterman (Stanford Postdoctoral Fellow). In addition, Peterman is a young female scientist (Ph.D. 2009).3. This study will train undergraduates (UCSB) in laboratory investigations and provide a component of graduate research for graduate students at UCSB and Stanford.4. The results of the proposed research will impact the geochronology community at large:o Thermal Ionization Mass Spectrometryo Secondary Ionization Mass Spectrometryo Electron Probe MicroAnalysiso (Laser Ablation) Inductively Coupled Plasma Mass Spectrometry