Annotated picture of a mylonitic shear zone. The large white potassium feldspar crystal (“porphyroblast”) was rolled to the left in a zone of penetrative, high-temperature shearing (mylonitic shear zone), Santa Catalina Mountains. Yellow arrows show sense of shear. Red lines are shear surfaces (“C-surfaces”), green lines are surfaces that formed by mica recrystallization in the plane of flattening, purple lines are shear surfaces that were rotated into the pressure shadow of the hard, resistant, K-feldspar porphyroclast. (photo by Jon Spencer)
Online resource: Spencer, J.E., 2006, A geologist's guide to the core complex geology along the Catalina Highway, Tucson Area, Arizona https://library.azgs.arizona.edu/item/AOFR-1552429673312-319
Photographer: Jon Spencer
Photo Date: circa 2006