2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 36
Presentation Time: 8:00 AM-4:45 PM

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

SINGLETON, John S., Department of Geological Sciences, University of Texas, Austin, TX 78712, jsingleton@mail.utexas.edu

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.