High temperature metamorphic processes in large orogens

点击翻译按钮获取中文摘要

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.