Print this pageA Comparison of Paired Monoclines in Central Utah: Origin, Timing, and Structural Style
Shelley A. Judge, Terry J. Wilson, David H.
Elliot, Kenneth A. Foland, and Douglas S. Kilmer
Ohio State University, Columbus, OH
The Rock and Dry monocline (RDM) and the Wasatch monocline (WM) are two northeast-trending, west-verging monoclines in central Utah. Both play key roles in the Mesozoic-Cenozoic tectonic framework of the region, because they lie in a transition zone corresponding with the eastern limits of the Sevier fold-thrust belt and the Basin and Range province and the western limit of the Colorado Plateau province.
The RDM forms the eastern front of the San Pitch Mountains. Kinematic data indicate that compression preceded flexure and continued through monocline development. Thrust-fold spatial associations and evidence for layer-parallel compression link RDM formation with west-vergent thrusting and regional compression associated with the development of the Sevier thrust belt. The RDM developed during latest Eocene backthrusting within the Gunnison thrust system in the Sevier thrust belt.
The WM forms the western front of the southern Wasatch Plateau. Kinematic data document multiple slip events and extension during flexure. Results indicate the WM is a drape fold over a west-verging normal fault. Paleocurrent patterns in Middle Eocene units suggest the WM was not a feature of high topographic relief at that time. Spatial relationships show an unconformity between the Crazy Hollow Fm and the Fm of Aurora; the latter unit progressively thins from W to E and onlaps against the monocline limb. Biotites from an ash flow tuff within the Aurora yielded 40Ar/39Ar dates of 38.0±0.2 Ma; therefore, WM flexure initiated after the Middle Eocene but before the Late Eocene ash flow tuff within the Fm of Aurora.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005