Collaborative Research: Quantifying the Dependence of Fabric and Rheology on Finite Strain for Naturally Deformed Rocks

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Rheology, a term used to describe material behavior, quantifies the relation between the observed deformation (strain) and the applied forces (stress). All aspects of rock deformation and evolution of the tectonic plates are a function of rock rheology over geological time scales. The difficulty in characterizing rock rheology occurs because of the extremely slow rates of deformation for geological processes and the polyphase (more than two minerals) nature of rocks. The researchers in this project use field data to constrain and quantify the relationships between progressive finite strain and developing fabrics, and thereby constrain rheology of naturally deformed rocks. The metamorphosed and deformed Seine conglomerates from northwestern Ontario are being studied because they contain a wide variety of rock types and a significant finite strain gradient. Detailed finite strain analysis of all clast (rock type) populations in these conglomerates allow calculations of the relative strain rates of the different clast populations at individual outcrops and show how the relative strength relationships change across the finite strain gradient. Detailed fabric and textural analyses of the different clast populations across the strain gradient are being conducted. Specifically, this analysis includes lattice preferred orientation, shape preferred orientation, and connectivity (wavelet analysis) of each mineral phase within each clast population. These fabric and texture data sets, when coupled with the finite strain data, will show how each different clast population accommodates finite strain. This approach explicitly addresses the relative importance of: (1) fabric development in the evolution of a clast population's deformation behavior during progressive finite strain, and (2) variations in initial composition, initial grain size, and initial fabric on deformation behavior.