The influence of mica for the development of quartz-LPO in quartz-feldspatic aggregates naturally deformed within a shear zone

The quartz-LPO analysis in L-S mylonitic rocks of the Palaeozoic basement that crops out near Giuncana, northern Sardinia, evidenced the role that micas have for the development of quartz-LPO during low-T deformation of polycrystalline quartz-feldspatic rocks. Mylonites developed within the Posada-Asinara right-hand shear zone, from primary quartzites, schists, gneisses and migmatites. In samples of gneisses and schists with mica <18%, quartz-LPO suggests low-T conditions, while high-T LPO patterns exist in two samples exceeding 18% micas. The high-T LPO have been interpreted as relic patterns, survivor of the low-T evolution because of their relatively high content of phyllosilicates, which enable inter-crystalline strain partitioning among quartz and biotite.