Sub-critical fracture and associated retrogression of garnet during mylonitic deformation

Garnets of the Alpine Fault mylonites were notably fractured and a detailed study was conducted to explain fracture mechanisms andassociated retrogression. The Alpine Fault mylonites formed during progressive deformation that started at 5 Ma. The garnets grew during the Rangitata orogenyand were older than the Alpine Fault by more the 100 million years. Three fracture types were recognized: garnet fill, narrow retrogressive fill and wide, isolating islands of garnet, retrogressive fill. It was found that types two and three predominate over garnet filled fractures.