EVIDENCE FOR 35-50 KM DISPLACEMENT ON THE CLOUDBURST-SUIZO DETACHMENT FAULT SYSTEM NORTH OF TUCSON, ARIZONA, AND RESTORATION OF A MESOZOIC HIGH-ANGLE FAULT SYSTEM

New geologic mapping in the Tortolita Mountains north of Tucson, done under the joint State/Federal STATEMAP program, adds support to interpretations of tens of kilometers of extension during tectonic exhumation of the Catalina metamorphic core complex. A large tiltblock north of the Tortolita Mountains consists of Proterozoic granite and Pinal Schist, overlain to the NE by a sequence of middle Tertiary volcanic rocks and conglomerate dipping 40-80° at its base and progressively less tilted up-section. Overlying, gently dipping conglomerate contains a large rock-avalanche breccia previously interpreted as granitic bedrock. Farther east in the Star Flat area on the east side of Black Mountain, and in the Black Hills north of Oracle, the Cloudburst detachment fault displaces moderately to steeply east-tilted volcanic and sedimentary rocks. The basal contact of the steeply tilted Tertiary sequence north of the Tortolita Mountains is truncated laterally and downward by the Suizo Mountains and Guild Wash detachment faults. Northeastward restoration of this depositional contact to its footwall equivalent requires at least 35 km of displacement. Restoration of more than about 50 km of displacement is unlikely because Paleozoic sedimentary rocks in the Galiuro Mountains are absent in the tiltblock. The tiltblock north of the Tortolita Mountains is broken and distended by antithetic, northeast-dipping normal faults, including the Owl Head Butte fault.

Restoration of 45 km of east-northeast (062°) extensional displacement places the Ragged Top fault exposed in the northern Silverbell Mountains (W of Avra Valley) on strike with the Mogul fault in the northern Santa Catalina Mountains. We hypothesize that these steep, west-northwest striking faults are both segments of a once continuous, regional Mesozoic fault system, north of which Late Cretaceous volcanic rocks and Tertiary strata directly overlie Proterozoic granite, and south of which is a complexly deformed assemblage of Paleozoic and Mesozoic rocks. We suggest that the Apache Pass fault zone in the Dos Cabezas Mountains is part of the same regional structure.