High temperature metamorphic processes in large orogens

大造山带的高温变质过程

• 批准号: RGPIN-2014-06034
• 负责人: Indares, Aphrodite
• 金额: $ 2.7万
• 依托单位: Memorial University of Newfoundland
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=567542
• 关键词: temperature; metamorphic; processes; large; orogens

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.

大陆山脉带（造山带），在构造板块碰撞过程中产生，是地球表面的一个基本特征，并构成地壳再循环的主要场所。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，更好地了解山区的地壳演化。现代变质岩石学的一个主要方向是通过评估地壳岩石随时间推移所经历的压力（埋藏深度）和温度（变质P-T-t路径）的变化，利用矿物中编码的信息来提供对造山过程的见解。微观分析和热力学模拟的最新发展使我们能够以前所未有的方式检索有关变质岩P-T-t演化的信息。然而，由于自然系统的复杂性，这种方法的使用是不平凡的，在一些情况下，仍处于实验阶段。在大型热造山带的情况下，变质研究特别具有挑战性，在这种造山带中，中下地壳在800ºC以上的温度下长期居住，是部分熔融、地壳流动、造山高原形成和地球历史上最大的山脉带系统（如今天的喜马拉雅山和西藏）发展所造成的大量质量重新分配的根源。现代活动的山脉带提供了造山构造的重要证据，但内部结构只有在侵蚀后才能显示出来。因此，现在暴露在被侵蚀的古老造山带核心地带的以前的热地壳，提供了山根作用过程的无与伦比的记录。典型的例子是中元古代的格伦维尔省，它构成了北美东部的一个主要构造单元，被视为现代喜马拉雅-西藏系统的典型古代类似物。该提案侧重于LHO中的高温（T）过程。其目的是：（I）通过探索矿物数据、P-T路径和时间之间的联系，提高我们解码造山麻粒岩（高温变质岩）的P-T -t记录的能力;（II）在现代地球动力学模型的框架内，通过解开和解释格伦维尔中部目前暴露的对比地壳水平的P-T-t特征，深入了解LHO是如何工作的。拟议的研究涉及综合使用前卫的方法，探索高T变质系统的适用性。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（如石英中的钛）来建立。此外，P-T路径和时间之间的联系将通过测定高T同位素系统（锆石中的U-Pb，石榴石中的Lu-Hf），并通过解释地球化学特征，生长温度（例如，锆石中的Ti）和纹理的背景下的年龄进行评估。预期结果将：为地球历史上最古老的LHO（格伦维尔）的地球动力学解释提供范例;提高对一般造山环境中高温地壳过程的理解;并测试有前途的前线技术在解释麻粒岩相岩石上的适用性。因此，他们将推进地壳演化领域的知识，并有助于加拿大地球科学的国际形象。拟议的研究涉及大量的研究生和本科生在现代技术相关的调查地球材料如何通过地质过程的变化，因此，广泛适用于地球科学相关的工作环境的培训。它还将使学生对地球系统的工作方式有更全面的了解。