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。

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.