LARAMIDE CONTRACTIONAL REACTIVATION OF OLDER MESOZOIC EXTENSIONAL FAULTS IN THE SOUTHERN MULE MOUNTAINS OF SOUTHEASTERN ARIZONA

Structural inversion of Late Jurassic-Early Cretaceous northwest-trending normal faults by southwest-northeast Laramide contractional deformation is present in the southern Mule Mountains, near Bisbee, AZ. The southwest-dipping Dividend and Gold Hill fault zones are mostly parallel and were both active as normal faults during the deposition of the Upper Jurassic-Lower Cretaceous Glance Conglomerate, each with dip-slip offsets over 1500 m. During the Late Cretaceous-Early Tertiary Laramide Orogeny, both of these faults were reactivated as reverse faults although to differing degrees. Lower Cretaceous strata of the Bisbee Group are draped over the eastern extent of the N70W-trending Dividend fault, essentially unbroken, as an anticline with a steeply dipping, overturned northeastern limb. Just 3.5 km to the southeast, the Gold Hill fault is a complex zone of anastomosing high and low angle faults that bound intricately deformed and uplifted blocks of Paleozoic strata as much as 0.8 km in width between extensive tracts of Lower Cretaceous Bisbee Group strata. Also included in the fault zone is a fault-bounded wedge of Lower Cretaceous Mural Limestone, quite out of place at a distinctly lower stratigraphic level. The eastern extent of the Gold Hill fault changes strike to N30W and becomes a much simpler, straighter fault heading southeast to the international border. A third fault, here called the Glance fault, splays southeast off the Gold Hill fault zone at Gold Hill, striking N30W, parallel to the eastern extension of the Gold Hill fault zone. The Glance fault dips 70 degrees to the northeast, has significant reverse-slip motion and, with new structural mapping, helps explain the geometry and kinematics of the contractional deformation along the Gold Hill fault zone.