The effects of composition and strain on quartz-fabric intensity in pebbles from a deformed conglomerate

Twenty-eight quartz c-axis fabrics from individual pebbles from a single outcrop of deformed conglomerate have been measured. These pebbles vary in composition and have undergone different amounts of strain. Contrary to expectations based on published results of computer simulated deformation by intracrystalline slip of pure quartzites, it is observed that fabrics are not stronger in the more highly deformed pebbles. Instead, the fabric strength is related to the quartz content of the pebbles. Pure quartzites show the strongest fabrics. As the percentage of non-quartz minerals increases up to 25% the strength of the fabrics rapidly decreases, though the influence of composition becomes less marked when impurities exceed 25%. These observations can be explained if the deformation of the impure quartzites included a contribution from a non-intracrystalline mechanism such as grain boundary sliding