Intragrain Oxygen-isotope Zoning and the Fast Grain Boundary Model: A New Approach to Thermal Histories and Fluid-rock Interactions

矿物是强大而微小的时间胶囊，记录了地球过去的事件和状况。解开这些地球化学时间胶囊涉及两个主要挑战：1)在微米尺度上精确和准确地测量矿物成分，2)将微尺度的矿物成分与构造尺度的地质事件联系起来。这个研究项目将利用最新的分析技术来研究美国西部一个构造独特地区的单个矿物中的氧同位素。测量的氧同位素模式将用于量化构造变形期间的温度、时间和水成分。因此，氧同位素数据将提供关于过去热量和流体运动的新的、非常详细的信息，这对于了解矿石的形成和地壳的变形是必要的。这项研究将扩展地球化学方法，包括分析和计算，将矿物的小规模数据转化为对宏观地质事件和过程的理解。该奖项由岩石与地球化学项目和EPSCoR（刺激竞争性研究实验项目）共同资助，将帮助新墨西哥矿业与技术学院的两名本科生和两名研究生进行研究培训。具体来说，高级学生将承担一个结合分析地球化学和计算建模技能的项目，这将为他们的职业生涯做好准备，这些职业需要熟练的技术和执行定量数据分析的能力。该项目还将帮助建立一名早期职业女性地球科学家的研究计划。单个矿物颗粒中氧同位素组成的空间变异性（分带）是迄今为止尚未开发的过去热事件和流体-岩石相互作用的记录。许多分带研究调查了矿物中的化学分带，但直到最近分析技术的进步才开启了同位素分带的研究。氧同位素分带对于监测变质条件和/或随时间变化的流体-岩石相互作用特别有用，因为矿物的氧同位素组成对温度和流体同位素组成很敏感。快速晶界（Fast Grain Boundary， FGB）概念和数值模型有助于将粒度传质与岩石微观结构和宏观结构联系起来，进而与更大尺度的传质构造驱动因素联系起来。因此，FGB和氧同位素分带测量共同代表了一种新的方法，用于开发有意义的、数据受限的岩石内部成分非均质性解释。因此，本研究将利用最先进的原位测量技术，结合FGB计算工具，研究保存在氧同位素分带中的几个美国西部变质岩心杂岩的热历史和流体历史。

Minerals are powerful, but tiny, time capsules of past Earth events and conditions. Unpacking these geochemical time capsules involves two major challenges: 1) precise and accurate measurement of mineral composition at the scale of micrometers, and 2) linking micro scale mineral composition to tectonic-scale geologic events. This research project will use recent advances in analytical technology to investigate oxygen isotopes in individual minerals from a tectonically unique region of the western United States. Measured oxygen isotope patterns will be used to quantify temperature, time, and water composition during tectonic deformation. Oxygen isotope data will thus provide new, highly detailed information about the past movement of heat and fluids, which is necessary to understanding ore formation and deformation of Earth's crust. This research will expand geochemical methodologies, both analytical and computational, for transforming small-scale data from minerals into understanding of big-picture geologic events and processes. This award is co-funded by the Petrology & Geochemistry program and EPSCoR (Experimental Program to Stimulate Competitive Research) and will help enable the research training of two undergraduate and two graduate students at the New Mexico Institute of Mining and Technology. Specifically, advanced students will undertake a project that combines skills in analytical geochemistry and computational modeling that will prepare them for careers that require technological fluency and the ability to perform quantitative data analysis. The proposed project will also help to establish the research program of an early-career female geoscientist.The spatial variability (zoning) of oxygen-isotope composition within individual mineral grains is, as yet, a largely untapped record of past thermal events and fluid-rock interactions. Many zoning studies have investigated chemical zoning in minerals, but only recently have advances in analytical techniques opened up investigation of isotopic zoning. Oxygen-isotope zoning is particularly useful as a monitor of changing metamorphic conditions and/or fluid-rock interactions over time because the oxygen-isotope composition of minerals is sensitive to temperature and fluid isotopic composition. The Fast Grain Boundary (FGB) conceptual and numerical model aid in linking grain-scale mass transfer to rock microstructure and macrostructure, and then to larger-scale tectonic drivers of mass transfer. Thus, FGB and oxygen-isotope zoning measurements together represent a new approach for developing meaningful, data-constrained interpretations of intragrain compositional heterogeneity. This research will therefore leverage state-of-the-art in situ measurement techniques, in combination with FGB computational tools, to investigate the thermal and fluid histories of several western US metamorphic core complexes as preserved in oxygen-isotope zoning.