Reaction-Weakening in Phyllonites Formed in Granite
Contribution to Book
Atlas of Mylonitic and Fault-Related Rocks
Princeton University Press
These examples of microstructures and textures associated with reaction weakening come from the Gessaman fault in southern Arizona, U.S.A., and were first described in Janecke and Evans (1988). Phyllonitic textures are concentrated in a 2-3 m wide zone formed in Proterozoic Oracle Granite. The protolith granite consists of 10-25 mm diameter quartz grains, 5-12 mm diameter orthoclase grains, 5-10 mm plagioclase grains, and minor amounts of biotite and accessory minerals. Deformation occurred during the early Tertiary, probably at temperatures of 250-400°C.
Evans, J. P., 1998, Reaction-weakening in phyllonites formed in granite, in: Atlas of mylonitic and fault-related rocks, A. W. Snoke, J. A. Tullis, and V. R. Todd, eds., Princeton University Press.