High temperature metamorphic processes in large orogens

大陆山带（造山带）是构造板块碰撞产生的，是地球表面的基本特征，构成了地壳循环的主要场所。我的研究计划的长期目标是利用我在变质岩石学方面的专业知识，更好地了解山带的地壳演化。现代变质岩石学的一个主要方向是利用其矿物编码的信息，通过评估地壳岩石随时间（变质P-T-t路径）的压力（埋藏深度）和温度的变化，提供对造山过程的见解。微分析和热力学建模的最新发展使我们能够以前所未有的方式检索变质岩的P-T-t演化信息。然而，由于自然系统的复杂性，这种方法的使用不是微不足道的，在一些情况下，仍处于实验阶段。在大型热造山带（LHOs）的情况下，变质学研究尤其具有挑战性，在这些造山带中，中下地壳在800摄氏度以上的温度下的长期停留是通过部分熔融、地壳流动、造山高原的形成和地球历史上最大的山带系统的发展而产生大量物质再分配的起源（例如今天的喜马拉雅山和西藏）。现代活跃的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，现在暴露在被侵蚀的古造山带核心区的以前的热地壳，提供了在山根运行过程的无与伦比的记录。中元古代格伦维尔省是北美东部的一个主要构造单元，是现代喜马拉雅—西藏构造体系的典型古类比。本文主要研究lho中的高温过程。其目的是：(1)通过探索矿物数据、P-T路径和时间之间的联系，提高我们对造山麻粒岩（高t变质岩）P-T -t记录的解码能力；（II）在现代地球动力学模型的框架内，通过揭示和解释目前在格伦维尔中部暴露的对比地壳水平的P-T-t特征，提供lho如何工作的见解。提出的研究包括综合使用先进的方法，并对高t变质系统的适用性进行了不同的探索。矿物数据和P-T路径之间的联系将通过热力学建模、岩石结构调查和微量元素测温（例如石英中的钛）来建立。此外，P-T路径与时间之间的联系将通过定年高t同位素系统（锆石中的U-Pb，石榴石中的Lu-Hf），以及在地球化学特征、生长温度（例如锆石中的ti）和结构的背景下解释年龄来评估。预计结果将：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（Grenville）；提高对造山带高温度地壳过程的认识；并验证了有前景的一线技术在麻粒岩相岩解释中的适用性。因此，他们将推进地壳演化领域的知识，并为加拿大地球科学的国际形象做出贡献。拟议的研究包括对研究生和本科生进行大量培训，使他们掌握与调查地球物质如何通过地质过程发生变化有关的现代技术，从而广泛适用于与地球科学有关的工作环境。它还将使学生对地球系统的工作方式有一个更全面的认识。

Continental mountain belts (orogens), produced during the collision of tectonic plates, are a fundamental feature of the Earth’s surface, and constitute major sites in which the Earth’s crust is recycled. The long-term goal of my research program is to develop a better understanding of the crustal evolution in mountain belts using my expertise in metamorphic petrology. A major direction of modern metamorphic petrology is to offer insights on mountain building processes by assessing the changes in pressure (depths of burial) and temperature that crustal rocks experience over time (metamorphic P-T-t paths), using information encoded in their minerals. Recent developments in microanalysis and thermodynamic modeling allow us to retrieve information on the P–T-t evolution of metamorphic rocks in unprecedented ways. However, owing to the complexity of natural systems, the use of such approaches is non trivial and, in several instances, still at the experimental stage. Metamorphic studies are particularly challenging in the case of large hot orogens (LHOs), in which protracted residence of the middle to lower crust at temperatures above 800ºC is at the origin of substantial mass redistribution by partial melting, crustal flow, formation of orogenic plateaux and the development of the largest mountain belt systems in Earth’s history (e.g. present day Himalayas and Tibet). Modern, active mountain belts offer vital evidence of orogenic structure, but the internal architecture is only revealed after erosion. Therefore, formerly hot crust presently exposed in the core zones of eroded ancient orogens, provides an unparalleled record of processes operating at the mountain roots. The type example is the Mesoproterozoic Grenville Province, which constitutes a major tectonic element in eastern North America and is viewed as the exemplary ancient analogue to the modern Himalaya-Tibet system. This proposal focuses on high temperature (T) processes in LHOs. It aims to: (I) improve our ability to decode the P–T –t record of orogenic granulites (high-T metamorphic rocks) by exploring links between mineral data, P–T paths and time; and (II) provide insight into how LHOs work, by unraveling and interpreting the P–T–t signatures of contrasting crustal levels presently exposed in the central Grenville, within the framework of modern geodynamic models. The proposed research involves integrated use of avant-garde approaches with variably explored applicability to high-T metamorphic systems. Links between mineral data and P–T paths will be established by means of thermodynamic modeling, investigation of rock textures, and trace element thermometry (e.g. Ti-in-quartz). In addition, links between P–T paths and time will be assessed by dating high-T isotopic systems (U-Pb in zircon, Lu-Hf in garnet), and by interpreting the ages in the context of geochemical signatures, temperatures of growth (e.g. Ti-in-zircon) and textures. The results are expected to: provide a paradigm for the geodynamic interpretation of the oldest LHO in Earth’s history (Grenville); improve understanding of high-T crustal processes in orogenic settings in general; and test the applicability of promising front line techniques on the interpretation of granulite facies rocks. Therefore, they will advance knowledge in the field of crustal evolution, and contribute to the international profile of Canadian geosciences. The proposed research involves substantial training of graduate and undergraduate students in modern techniques relevant to investigation of how Earth materials change through geological processes, and therefore, with wide applicability to Earth Science-related work environments. It will also allow students to develop a more global appreciation of how Earth systems work.