Paper No. 2
Presentation Time: 1:25 PM


SINGLETON, John, Department of Atmospheric, Oceanic, and Earth Sciences, George Mason University, 4400 University Drive, Fairfax, VA 22030 and STOCKLI, Daniel F., Department of Geological Sciences, University of Texas at Austin, Austin, TX 78712,

We present thermochronologic and geochronologic data that constrain the slip history of the Buckskin-Rawhide detachment fault in west-central Arizona, one of the largest extensional fault systems in the North American Cordillera. (U-Th)/He zircon and apatite thermochronology, integrated with 40Ar/39Ar geochronology of syn- and postdetachment volcanic rocks, indicate that large-magnitude extension associated with the detachment fault initiated ~22 ± 1 Ma and continued until ~12-11 Ma in the southwestern portion of the Buckskin-Rawhide metamorphic core complex. The inception of detachment faulting was approximately coeval with widespread plutonism in the footwall. Apatite (U-Th)/He footwall cooling ages from the breakaway zone in the western Bouse Hills to upper greenschist-facies mylonites in the southern Buckskin Mountains indicate that the slip rate on the detachment fault was 2.8 +0.7/-0.5 km/m.y. during the early Miocene. Space-time patterns of hanging wall tilting suggest that at 17-16 Ma a secondary detachment fault breakaway developed ~12 km northeast of the primary detachment fault breakaway. Proximal conglomerates deposited in a supradetachment basin adjacent to the secondary breakaway scarp were displaced 8-10.5 km northeast in the middle Miocene by the Buckskin-Rawhide detachment fault at a slip rate of ~2.1 ± 0.5 km/m.y. The total displacement across the detachment fault system in the southwestern portion of the core complex is 26 ± 5 km, well short of the previous estimate of 66 ± 8 km across the entire core complex. We propose that total displacement on the Buckskin-Rawhide detachment fault system increases in the slip direction to ~35-40 km at the northeastern end of the exposed footwall, correlating to time-averaged slip rates no greater than ~4 km/m.y.