Deformation Bands in Calcite and Quartz Crystals

Deformation bands in some of calcite and quartz grains in a naturally deformed calcite-quartz vein found in the Sangun metamorphic formation near the Kawayama mine, Yamaguchi Pref., Western Japan, have been described. The deformation bands in calcite are inclined at moderate angles to the active glide plane, a {0112} plane (e1), and the axis of the lattice rotation in the band is parallel to the glide plane and normal to the glide direction, the edge [e1: r3]. The angle between the c-axis of the host crystal and the surface of the band boundary is between 14° and 44°, and the angle between the glide direction and the surface of the band boundary is between 40° and 70°. For many of the deformation bands the lattice in the band approaches the completely twinned condition for e1, while in the host crystals the lattice is about 10 per cent twinned on e1. The sense of lattice rotation in the band is opposed to that for twin gliding on e1. The maximum value of the angle of lattice rotation in the band is 87°. Generally, the band boundaries are distinctly displayed by the sharp change in the trend of e1 and in the degree of e1 twinning, but not by such a manner as that e1 twinning progressively increases toward the margins of the band. For the deformation bands, in which the angle of lattice rotation exceeds 44°, the band boundaries are commonly displayed as a sharp discontinuous plane whose crystallographic location can be directly measured by the U-stage.
The crystallographic location of the deformation bands in quartz has been tentatively determined on the basis of assumption that the rotational axis of shift in the lattice orientation from the host to the band coincides with either the a-axis or the a*-axis. At this time many of the quartz deformation bands are inclined at high angles to the c-axis. They are approximately tautozonally oriented and are grouped in two sets of planes in the system concerned. The rule for establishing the directions of the principal stresses developed in the system concerned during the deformation related to the formation of the deformation bands, previously introduced by the senior author (1961a and 1963), has been successfully used also for the present specimen. It has been clarified that the sense of lattice rotation in the band for quartz deformation bands is opposed to that for the calcite deformation bands of the present type in the same stress system.