LOW-ANGLE THRUST RELATIONSHIPS IN THE NORTHERN CHIRICAHUA MOUNTAINS, ARIZONA AND EVIDENCE FOR MULTIPLE PHASES OF CONTRACTIONAL DEFORMATION

The western United States is an archetypal Cordilleran system and the retroarc thrust belt can be traced for 1000s of kilometers along strike. However, due to multiple episodes of structural and magmatic overprinting, the nature and existence of a thrust belt in the southern U.S. Cordillera is uncertain. To resolve the complex tectonic history of the region, detailed geologic mapping in the northern Chiricahua Mountains, Arizona was undertaken. We identified a low-angle thrust fault placing Paleozoic carbonate rocks structurally over Upper Cretaceous to Paleogene volcaniclastic rocks interpreted to be deposited syn-kinematically. Geochronological analyses are underway to help constrain the age of these synorogenic deposits. The synorogenic rocks overlie Lower Cretaceous sedimentary rocks of the Bisbee Group in a spectacular angular unconformity. The map relationship suggests at least two phases of contractional deformation including; 1) folding/tilting of the Bisbee Group followed by erosion and 2) low-angle thrusting. If low-angle thrusting similar to the Chiricahua Mountains is also present in other areas in southern Arizona, it may help explain evidence for thick crust during the Late Cretaceous to Paleogene (Laramide time).