Rock deformation studies in the Mineral Mountains and Sevier Desert of west-central Utah: Implications for upper crustal low-angle normal faulting

Publication Type  Journal Article
Year of Publication  2001
Authors  Anders, M. H.; Christie-Blick, N.; Wills, S.; Krueger, S. W.
Journal Title  Geological Society of America Bulletin
Volume  113
Issue  7
Pages  895-907
Journal Date  Jul
ISBN Number  0016-7606
Accession Number  ISI:000169670400008
Key Words  brittle rock deformation; fault zones; normal faults; sevier desert; utah; seismic-reflection data; snake river plain; united-states; range province; extensional tectonics; cenozoic extension; eastern basin; orogenic belt; heat-flow; growth
Abstract  

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 dear 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 con-tact. 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. I, ARCO Meadow Federal No. 1, and Argonaut Energy Federal No. I 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 (similar to5 km and < 300 degreesC) 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 degreesC 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.

Notes  

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