Rock Structure and Quartz Fabric in a Thrusting Shear Zone: the Kiyomizu Tectonic Zone in Shikoku, Japan

A remarkable thrusting shear zone has been found near the southern margin of the Samba-gawa crystalline schist zone in Central Shikoku, representing a frontal zone characterized by thrusting shear movement towards the south, the movement having been caused by the horizontal compression and the consequent upward swelling of the metamorphic zone. The zone has been designated as the Kiyomizu tectonic zone. Rock structures, such as bedding-schistosity or -foliation, fracture-cleavage, closely spaced shear-cleavage, and the related lineations, have been geometrically analysed for rocks both in the tectonic zone and in the northern metamorphic zone proper. On the basis of these geometrical features, the history of development of the tectonic zone has been discussed. Then, the quartz fabric of rocks in the zone has been analysed. The pattern shows an intimate relation between the position of maximum and the direction and the sense of shear on the bedding-schistosity plane of papery schists characteristically found in the tectonic zone. From this definite relation has been deduced a working hypothesis about the orientation of quartz in the flow of rocks, especially in those cases of strong recrystallization or segregation under stress condition.