EVIDENCE FOR A SYNCLINE-ANTICLINE PAIR AND MULTIPLE PHASES OF DEFORMATION DURING THE LARAMIDE OROGENY IN THE DRAGOON MOUNTAINS, ARIZONA

The nature and extent of shortening associated with the Laramide Orogeny in the southern U.S. Cordillera is uncertain. Laramide-related deformation is overprinted by younger low-angle and high-angle normal faults and obscured by Cenozoic magmatism, creating barriers to understanding contractional deformation in the region. To help resolve the complex tectonic history of the region, we conducted detailed geologic mapping and collected new structural data in the central Dragoon Mountains, Arizona. The area is characterized by a large anticline-syncline pair that is locally overturned. Lower Cretaceous Bisbee Group rocks are located in the core of the syncline and were deposited unconformably on upper Paleozoic (Pennsylvanian to Permian) carbonate rocks. Also in the core of the syncline are Proterozoic basement rocks and Cambrian sedimentary rocks that have been previously interpreted to be juxtaposed with the Bisbee Group along a thrust fault, a normal fault, or an unconformity. New structural measurements and geologic mapping indicate the Proterozoic to Cambrian rocks were originally juxtaposed against Bisbee Group rocks along a reverse fault and that this fault contact was subsequently cut by high-angle normal faults, presumably during Miocene “Basin and Range” extension. This suggests that the Bisbee Group rocks were, at least locally, tectonically buried in the footwall beneath the Proterozoic to Cambrian rocks. Samples collected from the Bisbee Group throughout the map area will be analyzed to constrain maximum burial temperature using Raman spectroscopy of carbonaceous material (RSCM) to evaluate its thermal history. Fault relationships in the Dragoon Mountains have implications for regional tectonic reconstructions of the southern U.S. Cordillera.