Deciphering the metamorphic record of orogenic belts

在地球历史的大部分时间里，大陆地壳的演化是以超级大陆的形成和分裂为标志的，超级大陆是通过构造板块的碰撞和山带（造山带）的发育而形成的。在这些环境中，大陆地壳逐渐被掩埋和加热，导致相关岩石的变化（变质作用）。我的研究计划的长期目标是利用我在变质作用方面的专业知识促进对山带地壳演化的理解。***造山过程中压力和温度随时间的变化（PTt路径）被编码在矿物组合中，由于最近微分析和热力学建模的发展，这种记录可以以前所未有的方式揭示。然而，在复杂的自然系统中，这项任务并非微不足道，而且部分处于探索阶段。在大型热造山带（LHOs）的情况下，变质学研究尤其具有挑战性，在这些地区，中下地壳在800 ~ 800℃的长期停留导致部分熔融和地壳流动，造山带高原的上升和地球历史上最大的造山带的发展（例如今天的喜马拉雅-西藏）。现代山带为造山构造提供了重要证据，但内部构造只有在侵蚀后才会显露出来。因此，暴露的侵蚀古造山带核心区提供了山根过程的关键记录。一个典型的例子是中元古代的格伦维尔省，它形成了北美东部的一个主要构造元素，被视为现代喜马拉雅系统的古代类似物。***本提案主要针对lho中的高t工艺。该项目旨在通过探索矿物、PT路径和时间之间的联系，解码格伦维尔省麻粒岩（高t变质岩）的PTt记录。矿物结构将通过复杂的成像技术进行评估，PT路径将通过基性麻粒岩的热力学建模来推断，这是一种信息丰富的岩石类型，其模型仅在两年前才可用。时间维度将通过对独居石、锆石和石榴石的高T同位素系统定年，结合在单一岩石尺度上很少使用的方法，并通过将年龄与地球化学特征、生长和纹理的T结合起来，来增加时间维度。***这些结果将为地球历史上最古老的LHO的地球动力学解释提供一个范例，从而揭示地壳随时间的演化，提高对一般高t造山过程的认识，并测试变质岩石学的前沿方法。拟议的研究包括对研究生和本科生进行大量的现代分析、成像和建模技术培训，这些技术与地球物质如何通过地质过程变化的调查有关，并广泛应用于与地球科学有关的工作环境，并将促进对地球系统如何工作的更全面的认识。＊＊＊＊＊

For most of the Earth's history the evolution of continental crust is marked by the formation and breakup of supercontinents, which are assembled through collision of tectonic plates and development of mountain belts (orogens). In these settings, continental crust is progressively buried and heated up, leading to changes (metamorphism) in the rocks involved. The long-term goal of my research program is to advance understanding of crustal evolution in mountain belts using my expertise in metamorphism. *** Changes in pressure and temperature over time (PTt paths) during orogeny are encoded in mineral assemblages, and this record can be revealed in unprecedented ways due to recent developments in microanalysis and thermodynamic modeling. However, in complex natural systems, this task is non-trivial and is partly at an exploratory stage. Metamorphic studies are particularly challenging in the case of large hot orogens (LHOs), where long residence of middle to lower crust at T > 800ºC results in partial melting and crustal flow, rise of orogenic plateaux and the development of the largest orogens in Earth's history (ex. present-day HimalayasTibet). Modern mountain belts offer vital evidence of orogenic structure, but the internal architecture is only revealed after erosion. Hence, exposed core zones of eroded ancient orogens provide key record of processes at mountain roots. A classic example is the Mesoproterozoic Grenville Province, which forms a major tectonic element in eastern North America and is viewed as an ancient analogue to the modern HimalayaTibet system. *** This proposal focuses on high-T processes in LHOs. It aims to decode the PTt record of granulites (high-T metamorphic rocks) from the Grenville Province, by exploring links between minerals, PT paths and time. Mineral textures will be assessed by sophisticated imaging techniques, and PT paths will be inferred by thermodynamic modelling of mafic granulites, an informative rock type for which models have only become available 2 years ago. The time dimension will be added by dating high-T isotopic systems in monazite, zircon and garnet, with a combination of methods rarely used at the scale of a single rock, and by integrating ages with geochemical signatures, T of growth and textures. *** The results will shed light on the evolution of the Earth's crust with time, by providing a paradigm for the geodynamic interpretation of the oldest LHO in Earth's history, improving insight on high-T orogenic processes in general, and testing cutting-edge approaches in metamorphic petrology. The proposed research involves substantial training of graduate and undergraduate students in modern analytical, imaging and modeling techniques relevant to investigation of how Earth materials change through geological processes, with wide applications to Earth Science-related work environments, and will promote development of a more global appreciation of how Earth systems work. *****