Mechanisms of metamorphic microstructure formation

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The microstructure of a metamorphic rock defines the three-dimensional microscopic distribution of the sizes, shapes, and abundances of the grains it contains, and the spatial arrangement of the grain boundary network separating them. It therefore significantly influences some of the most elemental properties of our planet's crust, including the way it transmits seismic waves, or the dissipation of thermal anomalies resulting from tectonic processes. However, the origin of rock microstructure is one of the least understood aspects of metamorphic petrology but it is known that the microstructure is a result of and provides direct insight into the mechanisms of fundamental, sub-microscopic processes such as mass transfer by chemical diffusion between crystals as well as molecular attachment and detachment at crystal interfaces, their driving forces, and the extent of disequilibrium experienced by the rock during their operations. The proposed research will result in a better understanding of metamorphic microstructure formation and will help to unlock the petrogenetic record of key processes associated with metamorphism. High-resolution X-ray micro--computed tomography available in the applicant's laboratory is essential for this research and will be systematically integrated with elemental, isotopic, geochronological, and crystallographic datasets of natural samples in order to quantify the spatial and temporal extent of chemical and mechanical disequilibrium as drivers of metamorphic reaction and microstructure evolution. An important focus of the research will be on the kinetics and molecular mechanisms of diffusive fluxes across polycrystalline aggregates as well as the physico--chemical properties of mineral interfaces and their influence on crystal growth aiding in the reconstruction of the timescales and rates of metamorphic processes. Furthermore, links will be established between the fundamental, rock--forming processes and large--scale, tectonic processes such as continent-continent collision during mountain belt formation or the thinning of lithosphere. This research will increase the competitiveness of Canada's earth sciences sector contributing to public's intrinsic interest in minerals and rocks and how they form. Direct applications will provide links to the resource extraction industries which form an important segment of the Canadian economy.