A DUCTILE NORTH-VERGENT SHEAR ZONE IN THE FOOTWALL BLOCK OF THE SOUTHWEST-VERGENT CATALINA DETACHMENT FAULT, SOUTHEASTERN ARIZONA

The Catalina detachment fault is the range-bounding fault on the southwest margin of the Catalina-Rincon metamorphic core complex of southeastern Arizona. This middle Tertiary gently-dipping normal fault has a down-to-the-southwest sense of slip. Along the range front, mylonites that are exposed within ~600 m structurally below the fault display foliations subparallel to the fault and lineations subparallel to the transport direction on the fault. Sense-of-shear indicators in these mylonites are overwhelmingly top-to-the southwest. These observations strongly suggest a kinematic link between the mylonites and the detachment fault.

However, in the Redington Pass area—located in the center of the complex, between the Rincon and Catalina Mountains—many mylonites display anomalous lineation trends and shear-sense indicators that cannot be kinematically linked to the Catalina detachment fault. Like the fore-range mylonites, these anomalous mylonites (1) are derived from the Precambrian Oracle Granite and the Eocene Wilderness Granite, (2) post-date Laramide-age deformation, and (3) are located within a few hundred meters structurally below the detachment fault (the detachment fault is here exposed as two klippen in the center of Redington Pass). But, unlike the fore-range mylonites, these anomalous mylonites comprise a distinct WNW-trending shear zone bounded on both sides by nonmylonitic granite. Lineations within this zone trend north-northeast, deviating 40° to 60° from the transport direction on the detachment fault. Shear sense indicators in this zone are predominantly top-to-the-north. These observations present a conundrum within one of the classic metamorphic core complexes of the North American Cordillera.