A demonstration of the interdependence of the degree of quartz preferred orientation and the quartz content of deformed rocks

Abstract

The orientation of quartz c-axes has been determined from mineralogically distinct layers of several metamorphic rocks. Individual specimens were chosen for which the external conditions of deformation could be assumed to be constant, the only significant variation within a specimen being in mineralogical composition. Conversely, the suite of specimens was chosen to represent a range in temperature, pressure, stress, finite strain and strain rate; the different orientation patterns that were observed demonstrate the operation of different, dominant orienting mechanisms. A detailed analysis of these specimens reveals a linear correlation between quartz content and the degree of preferred orientation of the quartz; the orientation pattern approaches random as the quartz content approaches zero. No correlation between degree of preferred orientation and any other parameter was found.It is concluded that the dispersion of the patterns of preferred orientation resulted from grain boundary sliding between the quartz and matrix.