VORTICITY ANALYSIS IN A METACHERT FROM THE SAMBAGAWA BELT, SW JAPAN

Common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c-axis preferred orientation patterns. In such rocks information is also commonly available on the orientation and magnitude of the finite strain. These features can be used to derive two independent estimates of the degree of non-coaxiality during deformation. In an example from the Sanbagawa Belt, SW Japan, the two methods give consistent results and show that deformation was intermediate between simple and pure shear. Such types or progressive deformation over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high P-T rocks in the region.