Crustal deformation processes in continental collision zones

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Continental collision zones form extensive mountain ranges and high plateaus. The dramatic rise of mountain belts such as the Himalaya also influences global climate and ocean geochemistry, leading to long-term environmental changes and faunal extinctions. To understand these agents of global change, it is therefore important to constrain the timing and mechanisms of major mountain growth episodes. One of the most significant advances in orogenic studies has been the realization that mountain belts are built on a weak, partially molten mid-crustal layer that is exhumed in orogenic cores. Although numerical modelling highlights the importance of this layer for mountain building, its tectonic evolution remains poorly understood.   The principal focus of this research proposal is the study of highly-deformed rocks metamorphosed at mid-crustal depths, which are now exposed near the centre of mountain belts. The Himalayan system is chosen as a natural laboratory for this study because it offers unprecedented exposure of rocks from this mid-crustal layer, as well as providing excellent controls on tectonic plate configuration, convergence rates, and environmental consequences. The main objectives are to determine the deformation history of the exhumed middle crust, and to evaluate the level of structural interactions with its overlying unmetamorphosed sedimentary rocks during post-collision deformation. The research will also evaluate the rates at which processes such as thickening, crustal extrusion, and exhumation take place in various segments of the orogen.   Although the Himalaya is the orogen that inspires many models of collisional orogenesis, it is also one of the most incompletely mapped and understood. This research will lead to a better understanding of processes involved in exhumation of metamorphic rocks within active orogenic belts, more specifically in their early stages of evolution. This research will provide key architectural control to refine numerical modelling of mountain belts, which in turn will yield insight into the evolution of other, older, more deeply exposed belts such as the Mesoproterozoic Grenville or the Paleoproterozoic Trans-Hudson orogens in Canada.