Geodynamics of Cenozoic extension along a transect across the Colorado River extensional corridor, southwestern USA

Abstract

The Colorado River extensional corridor in southwestern North America is one of Earth's most highly extended regions of continental crust. The central part of the belt includes three imbricate, regionally northeast-dipping extensional detachment faults. The Plomosa detachment fault in the northern Plomosa Mountains in western Arizona, the middle of the three faults, dips northeastward beneath the giant Harcuvar metamorphic core complex. Approximately 1 km of lower Miocene clastic sediments, lava flows, and rock-avalanche breccias were deposited in the northern Plomosa Mountains before initiation of the Plomosa detachment fault and division of the strata into two basins with different stratal accumulations following breakup. Both the detachment-fault lower plate and upper plate were then broken and tilted by normal faults. The upper plate was fragmented into numerous fault blocks and its extension-parallel width was approximately doubled. Application of critical-taper theory to delayed basin fragmentation suggests that southwestward tilting of the land surface and underlying normal faults led to normal-fault initiation and wedge breakup.