Experimental investigation on the fabric evolution and strain localization of quartz with and without the presence of muscovite

Abstract

Deformation experiments of synthetic quartz–muscovite aggregates were performed to high shear strains at dislocation creep conditions in quartz. In previous studies, axial compression experiments were conducted on quartz aggregates to develop a better understanding of the relationship between flow strength and lattice preferred orientation with varying percentages of muscovite. Other analyses have shown a relationship between the topology of second phases and the aggregate strength of the material. When the second phase exceeds a threshold percent within the aggregate, it becomes the mechanically controlling phase. In the case of muscovite in a quartzite, when the muscovite becomes abundant enough to develop an interconnected framework throughout the aggregate it becomes the controlling phase of the aggregate. This study demonstrates that at a volume percent between 10% and 25% muscovite there is a mechanical transition between a quartz-dominanted and muscovite-dominanted aggregate. The development of C’ shear bands in muscovite-present aggregates are interpreted as a weakening mechansim and aid in the redistribution of muscovite through processes such as dissolution–precipitation and recrystallization. In 100% quartz aggregates, strain localization is observed through geometrical softening where at the onset of recrystallization, c-axis orientations transition from prism [c] to rhomb <a>. Localization of strain is intrepreted as an increase in strain rate in the highest strained regions, which is consistent with the theory of the paleowattmeter where the recrystallized grain size is dependent on both stress and strain rate.