Arizona MCC

The particular interest of this website will be the MCCs present in the state of Arizona. The figure below (Reynolds, et al., 1980) details the placement of the MCCs. The general trend is NW and parallel to the edge of the Colorado Plateau and the Transition Zone.


Timing: Arizona

  The Cenozoic dates assigned to the Arizona Core Complexes  post-date the two major deformation events of the western US, namely the Sevier (~140 Ma - 60 Ma) and Laramide (~80 Ma - 40 Ma) Orogenies. Yet pre-date the Southern Basin and Range extension and rifting events (~25 Ma) (Coney, 1980, dates are Jones, lecture notes). See Arizona Geologic History.  Their formation began 10 - 30 My before the Pacific and North American Plates made contact and formed the San Andreas Fault and subsequent back arcs and Basin and Range extension (Coney and Harms, 1984).

To summarize:

Catalina Complex

The Santa Catalina-Ricon Mountains are in southeastern Arizona just outside of Tucson, Arizona. This complex has been fairly heavily studied and is considered to be a typical Southern Basin and Range MCC. Mid-Tertiary extension lifted the rocks (Dickinson, 1991) from a depth of about mid crust to 1.5 km above the valley floor.  (Figure Davis, 1987)

A progression in the transformation of the rocks of the complex can be seen by the progression of deformed rocks:  Mylonites and ultramylonites were "derived from the Precambrian and Tertiary quartz monzonites; chloritically altered microbreccias derived from the mylonite and ultramylonite; fine-grained microbreccias (cataclasite and ultracataclasite) derived from the chloritically altered breccias; the detachment fault (or decollement) separating cataclastic and mylonitic rocks below from nonmylonitic, noncataclastic and mylonitic rocks below from nonmylonitic, noncataclastic cover rocks above; and some folded Paleozoic cover rocks." (Davis, 1986)

The detachment fault is considered to be a low angle normal fault. The uplifted areas have also been deformed by the Basin and Range extension in the region after the main development of the core complex (Myers, 1994).