About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

Pacific Section of AAPG


The Geologic Transition, High Plateaus to Great Basin - A Symposium and Field Guide (The Mackin Volume), 2001
Pages 425-425

Low angle detachment along the Great Unconformity near the Colorado Plateau- Basin and Range breakaway: arguments against a tipped crustal section in the Gold Butte area, southern Nevada: Abstract

K. E. Karlstrom, M. C. Quigley, S. Bowring, E. Kirby, S. Hook, M. Heizler


Low angle extensional faults in the southern Virgin Mountains follow the Great Unconformity over lateral distances of >1000 km2. Detachment took place along subhorizontal bedding horizons in Cambrian Tapeats, Bright Angel, and Muav formations such that thinned flat-lying para-autochthonous sections of these lower Paleozoic rocks remain in the footwall adjacent to Proterozoic basement over a wide region. Above the detachment, extensional allochthons containing upper Paleozoic through Tertiary (18 Ma) rocks exhibit 30–80° E-tilting due to westward translation. This implies that major breakaway faults in this region initiated and moved at low angle and had ramp-flat geometry analogous to thrusts. Thus, isostatic footwall uplift is not required to explain the presence of low angle faults. Instead, Paleozoic cover was translated westward in domino blocks sliding generally along the Great Unconformity for tens of km west of the Grand Wash fault. Similar relationships are observed in the North Virgin Mountains and other para-autochthonous Proterozoic culminations north of the Gold Butte block, suggesting that this low-angle fault system forms a regional ramp-flat detachment system west of the Colorado Plateau. Ar-Ar dating of K-feldspars across the Gold Butte block show Proterozoic cooling ages and a general younging to the west, consistent with deeper exposed levels. Thermal models suggest the west end of the block was at depths <10 km prior to Miocene extension rather than at 15–18 km deep as suggested by the tilted crustal section model.


Copyright © 2009 by AAPG Pacific Section and Utah Geological Society