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1 Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964-8000, USA
2 ARCO Exploration and Production Technology, 2300 West Plano Parkway, Plano, Texas 75075, USA
The Cave Canyon detachment, a low-angle normal fault that crops out in the Mineral Mountains, west-central Utah, has been interpreted as a hanging-wall splay of a much larger structure (the Sevier Desert detachment) that was influential in development of the idea that low-angle normal faults play a role in crustal extension. The Cave Canyon detachment provides expectations for the deformational features that might be expected along the hypothesized Sevier Desert detachment, which is not exposed in outcrop and is inferred to exist primarily on the basis of seismic reflection data.
The footwall of the Cave Canyon detachment is characterized by a 200-m-thick granite cataclasite, which exhibits a clear decrease in grain size and increase in microfracture density as the fault surface is approached. Undulatory extinction in quartz and feldspar and abundant quartz deformation lamellae at distances more than 200 m from the fault surface are interpreted as related to cooling of the Miocene granite rather than to normal faulting. Although mylonitic textures have previously been described in the granite, we found no evidence for mylonitization in the footwall rocks. The hanging wall of the detachment is characterized by 9 m of deformed, partially dolomitized limestone, with a 2-m-thick carbonate mylonite at the contact. Deformation features include dynamic recrystallization, grain-size reduction, development of twinning with a strong preferred orientation, some grain-size layering, and undulatory extinction close to the fault. Static recrystallization overprints fossils and ooids at distances greater than 9 m.
Drill cuttings and some core recovered at similar distances above and below the hypothesized Sevier Desert detachment show no evidence for localized deformation (ARCO Hole-in-the-Rock No. 1, ARCO Meadow Federal No. 1, and Argonaut Energy Federal No. 1 wells). Fossils and ooids are undeformed in Paleozoic carbonate rocks within 3 m below the contact, and sandstone and conglomerate with rounded clasts lacking more than background levels of microfracturing are found in samples within 3 m above the contact. These features contrast markedly with those of the Cave Canyon detachment, which was active at a considerably shallower and cooler level in the crust (
5 km and <300 °C) than is implied for Paleozoic rocks beneath the Sevier Desert, once hanging-wall rocks are restored along the hypothesized detachment (9–14 km and 280–425 °C at the locations studied). The very different character of the two surfaces reinforces our earlier suggestion that beneath much of the Sevier Desert basin, the base of the Tertiary section is an unconformity rather than a low-angle normal fault.
Key Words: brittle rock deformation • fault zones • normal faults • Sevier Desert • Utah
This article has been cited by other articles:
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  N. Christie-Blick and M. H. Anders Regional structure and kinematic history of the Sevier fold-and-thrust belt, central Utah: Discussion GSA Bulletin, March 1, 2007; 119(3-4): 506 - 507. [Full Text] [PDF]
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J. C. Coogan and P. G. DeCelles Regional structure and kinematic history of the Sevier fold-and-thrust belt, central Utah: Reply GSA Bulletin, March 1, 2007; 119(3-4): 508 - 512. [Full Text] [PDF]
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 N. Christie-Blick, M. H. Anders, S. Wills, C. D. Walker, and B. Renik Observations from the Basin and Range Province (western United States) pertinent to the interpretation of regional detachment faults Geological Society, London, Special Publications, January 1, 2007; 282(1): 421 - 441. [Abstract] [Full Text] [PDF]
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P. G. DeCelles and J. C. Coogan Regional structure and kinematic history of the Sevier fold-and-thrust belt, central Utah GSA Bulletin, July 1, 2006; 118(7-8): 841 - 864. [Abstract] [Full Text] [PDF]
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 S. Wills, M. H. Anders, and N. Christie-Blick Pattern of Mesozoic thrust surfaces and Tertiary normal faults in the Sevier Desert subsurface, west-central Utah Am J Sci, January 1, 2005; 305(1): 42 - 100. [Abstract] [Full Text] [PDF]
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