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Timing and mechanisms of basement uplift and exhumation in the Colorado Plateau-Basin and Range transition zone, Virgin Mountain anticline, Nevada-Arizona

By
Mark C. Quigley
Mark C. Quigley
Department of Geological Sciences, University of Canterbury, Christchurch 8140, New Zealand
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Karl E. Karlstrom
Karl E. Karlstrom
Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA
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Shari Kelley
Shari Kelley
New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA
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Matt Heizler
Matt Heizler
New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA
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Published:
June 01, 2010

Structural, stratigraphic, and thermochronologic studies provide insight into the formation of basement-cored uplifts within the Colorado Plateau–Basin and Range transition zone in the Lake Mead region. Basement lithologic contacts, foliations, and ductile shear zones preserved in the core of the Virgin Mountain anticline parallel the trend of the anticline and are commonly reactivated by brittle fault zones, implying that basement anisotropy exerted a strong influence on the uplift geometry of the anticline. Potassium feldspar 40Ar/39Ar thermochronology indicates that basement rocks cooled from ≥250–325 °C to ≤150 °C in the Mesoproterozoic and remained at shallow crustal levels (<5–7 km) until they were exhumed to the surface. Apatite fission-track ages and track length measurements reveal a transition from slow cooling beginning at 30–26 Ma to rapid cooling at ca. 17 Ma, which we interpret to mark the change from regional post-Laramide denudational cooling to rapid extension-driven exhumational cooling by ca. 17 Ma. Middle Miocene conglomerates (ca. 16–11 Ma) flanking the anticline contain locally derived basement clasts with ca. 20 Ma apatite fission-track ages, implying rapid exhumation rates of ≥500 m m.y.−1. The apparently complex geometry of the anticline resulted from the superposition of first-order processes, including isostatic footwall uplift and extension-perpendicular shortening, on a previously tectonized and strongly anisotropic crust. A low-relief basement-cored uplift may have formed during the Late Cretaceous–early Tertiary Laramide orogeny; however, the bulk of uplift, exhumation, and deformation of the Virgin Mountain anticline occurred during middle Miocene crustal extension.

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GSA Special Papers

Miocene Tectonics of the Lake Mead Region, Central Basin and Range

Paul J. Umhoefer
Paul J. Umhoefer
Department of Geology, Northern Arizona University, Flagstaff, Arizona, USA
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L. Sue Beard
L. Sue Beard
U.S. Geological Survey, Flagstaff, Arizona, USA
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Melissa A. Lamb
Melissa A. Lamb
Geology Department, University of St. Thomas, St. Paul, Minnesota, USA
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Geological Society of America
Volume
463
ISBN print:
9780813724638
Publication date:
June 01, 2010

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