Pervasive Neogene extension approaching 100% in SW North America produced a suite of metamorphic core complexes. Core complexes form as rocks ascend from the middle crust along extensional, low-angle detachment faults. This illustration by Jon Spencer (AZGS retired) displays the distribution of core-complexes and their association with detachment faults and mylonitic rocks in northern Mexico, Arizona and eastern-most California.
Online resources:
Spencer, J.E., 2006, A geologist's guide to the core complex geology along the Catalina Highway, Tucson Area, Arizona. Arizona Geological Survey Open File Report, OFR-06-01, 38 p. https://library.azgs.arizona.edu/item/AOFR-1552429673312-319
Dickinson, William R., 1992, Geologic Map of Catalina Core Complex and San Pedro Trough: Arizona Geological Survey Contributed Map CM-92-C, map scale 1:125,000, 1 map sheet. https://library.azgs.arizona.edu/item/AGCM-1552427791236-991
Reynolds, S.J., 1985, Geology of the South Mountains, Central Arizona. Arizona Geological Survey Bulletin-195, 75 p., 1 map plate, scale 1:24,000. https://library.azgs.arizona.edu/item/AGSB-1552428268656-252
Photographer: Jon Spencer
Photo Date: 2018