2007 GSA Denver Annual Meeting (28–31 October 2007)

Paper No. 28
Presentation Time: 8:00 AM-12:00 PM


BYKERK-KAUFFMAN, Ann, Geological and Environmental Sciences, California State Univ, Chico, 400 W. 1st St, Chico, CA 95929-0205, abykerk-kauffman@csuchico.edu

The eastern Santa Catalina Mountains comprise a 200 km2 region of the footwall block of the Catalina metamorphic core complex. Although most of the Catalina complex is strongly affected by middle Tertiary top-to-the-southwest mylonitization and detachment faulting, the eastern Santa Catalina Mountains show no evidence of this event. Instead, a northeast-dipping sequence of Proterozoic through lower Cretaceous strata record two prior episodes of deformation: (1) Cretaceous thrusting and (2) early Tertiary top-to-the-east extensional ductile shearing and faulting.

Cretaceous thrusting is evidenced by the 20 km long Edgar thrust which places Proterozoic strata on Cambrian strata. This thrust is intruded by the 64 Ma Leatherwood Quartz Diorite and its associated swarm of quartz diorite porphyry sills. These sills are concentrated along the Edgar thrust and so pervasively intrude it that they largely obliterate its trace.

The Edgar thrust and the Leatherwood sills are cut by the Evans fault, a bedding subparallel ductile fault that omits section. Numerous tear faults accommodate transfer of this fault from one stratigraphic horizon to another. The Evans fault dies out northward and increases in throw southward. At its southern end, the Evans fault is intruded by one of the 50 Ma S-type Wilderness suite granites that dominate the lower plate of the Catalina metamorphic core complex.

A tectonite fabric, consisting of a bedding-subparallel foliation and an east-trending lineation, accommodates thinning of the strata and records top-to-the east shear. This fabric pervades the rocks throughout the area with two notable exceptions: (1) Wilderness Suite granites do not display this fabric, and (2) Paleozoic-Cretaceous strata in the northeastern corner of the area are free of the fabric. These rocks display a gradual southward fabric development and increase in fabric intensity accompanied by an increase in ductile strain as recorded by deformed Cretaceous limestone cobble conglomerates.

Together, the tectonite fabric and the Evans fault provide evidence for an early Tertiary episode of ductile top-to-the-east extension that predated middle Tertiary top-to-the-southwest mylonitization and detachment faulting in the Catalina metamorphic core complex.