Kinematic Evolution of Detachment Faulting In the Buckskin-Rawhide Metamorphic Core Complex, West-Central Arizona

Kinematic data from the Buckskin-Rawhide detachment fault system (>300 sets of slip lineations) record NE-directed extension, folding of the detachment fault, and a clockwise rotation of the extension direction. These data, combined with new geologic mapping, have implications for the development of detachment fault corrugations and the transition from NE-directed core complex extension to transtensional deformation and distributed ~E-W extension in the late middle Miocene.

The dominant orientations of detachment fault striae and footwall mylonitic lineations, and the regional detachment fault corrugation axis are all indicative of large-magnitude extension directed N40-45E. In contrast, NW- and SE-trending striae and kinematic indicators commonly preserved along NW- and SE-dipping limbs of detachment fault corrugations are compatible with reverse slip towards corrugation axes. This NW- to SE-directed reverse slip is interpreted to record flexural slip folding of the detachment fault and amplification of NE-trending corrugations towards the end of core complex extension (ca. 15-10 Ma). In the central and eastern Buckskin-Rawhide core complex, some segments of the detachment fault record a clockwise rotation of the extension direction to ENE- and E-directed extension. This change in the extension direction is consistent with the transition to ~E-W extension recorded by post-detachment faults. Dextral and transtensional slip along NW-trending faults represents the dominant mode of post-detachment faulting. The cumulative amount of dextral slip across the core complex is probably 7-9 km, which is the amount needed to restore footwall antiformal arches into parallelism with the dominant N40-45E extension direction.

Folding of the Buckskin-Rawhide detachment fault, clockwise rotation of the extension direction, and the transition to strike-slip- and transtensional-dominated faulting most likely reflect the increasing influence of dextral shear tectonics associated with the Pacific-North America plate boundary in the late middle Miocene.