Petrofabric Studies of Crystalline Limestone from the Southern Marginal Belt of the Sambagawa Metamorphic Zone in Central Shikoku, Japan.

The paper records the petrofabric analyses of limestone-schists from the Southern Marginal Belt of the Sambagawa Crystalline Schist Zone in Central Shikoku. The fabric of the limestone-schists shows a high degree of homogeneity not only in the thin section scale, but also in the hand specimen scale, in the outcrop scale and also in the more larger scale in the field. The orientation of the crystallographic axis c of calcite in the rocks shows marked concentration in the fabric diagrams, that representing a strong effect of the Einengung movement, as termed by B. SANDER (1950), during the recrystallization. The {0112} twinned lamellae of calcite grains in the limestone-schists were inferred to be the product of de-formation at the later stage under different stress plan, than the formation of lattice orientation, which must represent the main phase of deformation of the limestone-schists. The main directions of compression and tension most favourably oriented for the twinning on {0112} show almost reverse relation with respect to the geographical co-ordinates between the eastern and the western area, fabric diagrams in which show remarkable homogeneity respectively, the deformation being nearly coincident with ac plane, namely, perpendicular to B-lineation. This contrast was attributed to the difference in the geological position of the limestone-schists between both areas. The type of symmetry of the distribution diagram for {0112} twinned lamellae is defined by the degree of rotation of the movement. Two sets of the {0112} twinned lamellae in calcite grains of the limestone-schist at Motoyama have been developed successively in relation to the migration of main stress axes.