Preliminary study on the directional statistics of crush zones' strikes in the Kojaku Granite

Shimada, Koji   

In this preliminary study, more objective discrimination between orientations of small crush zones was carried out by means of directional statistics. Fitted number of mixture components of von Mises distribution is eight. A probability distribution function curve of eight components mixture shows two peaks. Crush zones principally depict dextral sense of shear along the system beta, and sinistral one along the system alpha-3. Plastically deformed biotite grains are observed in both crush zones. Deformation temperature of them seems to be higher. Statistically comparable development, nearly orthorhombic symmetry, and cross cutting relationship between the two systems suggest the development of crush zones in conjugate manner. This movement picture is inconsistent with continuing E-W shortening during late Quaternary. These lines of evidence suggest that crush zones observed at the site of Monju are old geologic structure.