Mylonite

This mylonite comes from a shear zone that marks the eastern margin of the Rockisle Granodiorite in the southern New England Orogen, Australia. The Rockisle Granodiorite is part of the Hillgrove Batholith, and was emplaced in the earliest Permian (295 Ma). Like many members of the Hillgrove Batholith, the pluton was deformed during the Hunter-Bowen Orogeny in the mid-late Permian. During this event the western side of the pluton was strongly sheared along its eastern margin, with east-over-west directed thrusting. Biotites from this specimen have revealed a Rb-Sr age of ~270 Ma, whiuch is interpreted to be the age of faulting. This sample from the shear zone has all the classic features of a mylonite, with well developed S and C planes, and a prominent stretching lineation defined by recrystallised biotite.