Delineation of deformation grades of low-strain granitoids using assemblages of elementary deformation textures

Based on microscopic observations of the Miocene Tokuwa granodiorite, central Japan, a method of delineating deformation grades of low-strain granitoids has been derived which utilizes assemblages of elementary deformation textures (EDTs) such as subdomains in quartz, bent twins in plagioclase and kink-bands in biotite. Although the granodiorite is comprised of equant grains and shows no evidence of deformation to the naked eye except for brittle fractures, it shows a variety of EDTs at the microscale. In thin section, assemblages of EDTs belonging to quartz, plagioclase or biotite are used for deformation grading of the corresponding rock. The deformation grading by EDTs based on quartz correlates with deformation grading based on plagioclase or biotite. Eigenvalues derived from a principal component analysis indicate that the first principal component explains approximately three-quarters of the variance of deformation grading by EDTs based on quartz, plagioclase, and biotite. The deformation grading by EDTs using quartz correlates well with the first principal component score. These results indicate that the deformation grading by assemblages of EDTs based on quartz, as well as on the first principal component score, is useful for deformation grading of low-strain granitoids.