Kinematic Interpretation of the Quartz Fabric of Triclinic Tectonites from Besshi, Central Shikoku, Japan

Three examples showing successive changes in quartz fabric pattern have been selected from triclinic tectonites from Besshi for geometrical and kinematic analyses of rock structure. After geometrical considerations, three sets of schistosity or cleavage surfaces have been discriminated, i.e., the axial-plane-schistosity, the first and the second transversal-schistosities, the latter two consisting of conjugate sets of s-surfaces. Quartz fabric patterns of these tectonites show an unmistakable triclinic character with respect to the situation of principal maximum, and their girdle patterns show a tendency to lie on certain small circles. Types of quartz pattern of these examples have been interpreted successfully in terms of orienting movements along the analysed s-surfaces after a working hypothesis about the rule of quartz orientation proposed in the preceding paper (G. KOJIMA and T. SUZUKI, 1958). It has been revealed that the quartz pattern represents mainly the last phase of orienting movement, that is, the phase of the second transversal-schistosity. Geometrical and kinematic relations between several types of quartz pattern have been discussed. The tectonites in question belong to the category of B⊥B'-tectonites. Geological conditions and kinematic character of deformation of successive phases of development of these s-surfaces have been considered. The result emphasizes the necessity of phase analysis of metamorphism.