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

Jon E. Spencer, John S. Singleton, Evan Strickland, Stephen J. Reynolds, Diane Love, David A. Foster and Roy Johnson
Geodynamics of Cenozoic extension along a transect across the Colorado River extensional corridor, Southwestern USA
Lithosphere (December 2018) 10 (6): 743-759

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. A seismic-reflection profile northeast of the northern Plomosa Mountains reveals strong, southwest-dipping reflectors that project up dip to metasedimentary tectonites in the southern Buckskin Mountains in the Harcuvar core complex. Restoration of displacement on the Buckskin and Plomosa detachment faults aligns the reflectors and tectonites with a Mesozoic shear zone in the footwall of the Plomosa detachment fault. In this restoration the combined shear zone dips northeastward rather than southwestward and projects up dip to the folds and thrusts exposed to the south and west of the northern Plomosa Mountains. This zone is interpreted as a segment of the Mesozoic Maria fold-and-thrust belt that influenced the geometry of younger detachment faults. The southwest-tilted, mylonitic lower plate of the Plomosa detachment fault includes, at its northern end, Orocopia Schist, which is a Cretaceous subduction complex that is better known from locations farther southwest and closer to the continental margin. Restoration of tectonic extension suggests that Orocopia Schist extends under the Harcuvar core complex and that a buoyant crustal root inherited from Cretaceous thrusting could not have been the cause of core-complex uplift unless the schist was emplaced by a mechanism other than subduction underplating. We propose that the rolling-hinge detachment-fault model combined with a highly mobile deep crust could account for Harcuvar core-complex genesis without a buoyant crustal root.


ISSN: 1941-8264
EISSN: 1947-4253
Serial Title: Lithosphere
Serial Volume: 10
Serial Issue: 6
Title: Geodynamics of Cenozoic extension along a transect across the Colorado River extensional corridor, Southwestern USA
Affiliation: University of Arizona, Department of Geosciences, Tucson, AZ, United States
Pages: 743-759
Published: 201812
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 112
Accession Number: 2019-002272
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., geol. sketch maps
N33°30'00" - N34°04'60", W114°19'60" - W113°30'00"
N33°19'60" - N34°19'60", W115°00'00" - W112°00'00"
Secondary Affiliation: Colorado State University, USA, United StatesArizona State University, USA, United StatesArizona Geological Survey, USA, United StatesUniversity of Florida, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 2019
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