RELATIONSHIPS BETWEEN STRAIN AND QUARTZ CRYSTALLOGRAPHIC FABRICS IN THE ROCHE MAURICE QUARTZITES OF PLOUGASTEL, WESTERN BRITTANY

An integrated microstructural and petrofabric study of the plastically deformed and partially recrystallized Roche Maurice quartzites of Plougastel, western Brittany, has revealed a clear correlation between the pattern of c-axis fabrics displayed by detrital quartz grains and the symmetry of the calculated strain ellipsoid. Within individual specimens c-axis fabrics of syntectonically recrystallized new quartz grains within the matrix are similar to those of detrital quartz grains. c axes of new grains locted within the relatively undeformed sections of the host detrital grains are commonly orientated at angles between 10 and 40 degree to the host c axis and are, in addition, statistically orientated at a higher angle to Z than their host c axes. These relationships are interpreted as indicating that both host grain control and the local strain field may have influenced the process of recrystallization; the relative influence of these factors is, however, unknown. Microstructural and petrofabric studies indicate that the Roche Maurice quartzites have been subjected to essentially coaxial strain histories.