GRAIN BOUNDARY CURVATURE DISTRIBUTION OF DYNAMICALLY RECRYSTALLIZED QUARTZ AGGREGATES IN A MYLONITE

Serrated grain boundaries are often observed in polycrystals deformed by dislocation creep. The shape of serrated grain boundaries contains a lot of information about the nature of intra-granular strain. Several authors have attempted to characterize shapes of grain boundaries by means of the Fourier spectra and fractal dimension. However, the shape parameters proposed by the above methods do not take into account processes operating on grain boundaries. It is difficult to represent a natural boundary shape with irregularity only by a few bulk parameters. The curvature distribution analysis is one of the methods that quantitatively characterize the morphological features of grain boundaries. Individual curvature at any specific point on a boundary can be examined with this method, and therefore, it is expected to extract morphological features accurately, even from boundaries with complicated shapes, and contribute to a better understanding of the grain boundary migration process. In this presentation, we apply this new method to sheared quartz aggregates deformed under higher greenschist facies condition collected from the Hatagawa mylonite zone in northeast Japan. The serration of grain boundaries is controlled by the misorientations and spacing of subgrain boundaries developed in the grain. We demonstrate that serrated grain boundaries have a common direction dependence of the curvature distribution and this morphological feature can be used for the determination of direction of grain boundary migration.