Characterization of Micro-Texture of Quartz Mylonite Deformation Process Using Fractal P-A Model

Quantifying the degree of quartz mylonite deformation, including the irregularities of the frequency distribution of the minerals involved, is one of the most challenging areas in mylonite analysis. Fractal modelling is here demonstrated to be an effective means to achieve this goal. The P-A (perimeter-area) model is used to quantify the irregularities of quartz, the main mineral component of mylonite, in the geometries. Five types of mylonites with different degrees of deformation within the foreland of the Moine thrust zone in NW Scotland were selected. The quartz was extracted from digital photomicrographs of multiscale-grey image grid data, and converted into vector data. The areas and perimeters of these quartz grains were calculated by GIS-based technologies. There is an increase in the degree of deformation of mylonite from type 1 to type 5, a D_ AP (the perimeter-area fractal dimension) increase from 1.20, 1.28, 1.38, 1.46 to 1.60, respectively. The results indicate quantitatively that quartz grains change from a regular to an irregular shape.