Brittle-Ductile Shear Zones Northwest of the Grenville Front Mylonite Zone, Killarney, Ontario

Small shear zones located northwest of the Grenville Front Mylonite Zone exhibit both a brittle and ductile deformation history. Textures reveal that an earlier mylonitic rock has been overprinted by one which demonstrates textures typical of brittle cataclasis. ductile deformation has occurred under greenschist facies conditions, while a later, brittle event has occurred below lower greenschist temperatures. These produce high shear strain values which lie between 14.44 and 10.79. Upper and lower age limits for the initiation of shear zones have been determined as being prior to the emplacement of pegmatite dykes, and up until the formation of brittle-ductile shear zones found locally. Thus, they have developed between 1400 ± 50 Ma and approximately 1100 + ? Ma.