Preferred Lattice Orientation of Quartz in Shear Deformation

The quartz fabrics of shear belts in granite of the Teshima district, Kagawa Pref., Japan, have been examined, in order to understand the nature of preferred lattice orientation of quartz developed by shear deformation. The strains in the shear belts are referred to the type of two dimensional strain with rotation. The stable pattern of the c-axis fabric of quartz in the shear belts appears in shear strain larger than ca. 1.80 and is characterized by two maxima with wide spreading on "pseudo-two-girdle", showing approximately orthorhombic symmetry whose symmetry planes are parallel to the principal planes of the strain ellipsoid of mean strain of the system concerned. The positions of two maxima coincide with the intersecting points of the "pseudo-two-girdle" which are situated on the plane containing the shortest and the intermediate principal axes of strain ellipsoid at the angle of ca. 30° to the latter axis. The one component girdle of the "pseudo-two-girdle" is a partial great-cicle girdle containing the two maxima and the intermediate principal axis, and the other component girdle would be regarded as two cro-ssed small-circle-like girdles, which cut across the plane of the longest and the shortest principal axes of the strain ellipsoid at the angle of ca. 40° to the latter axis, and whose intersecting points correspond to the positions of the two maxima. It has been concluded that the c-axis fabrics of quartz in the shear belts are mainly determined by the principal strain.