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Paleomagnetic and structural evidence for oblique slip in a fault-related fold, Grayback Monocline, Colorado

Joya Tetreault, Craig H. Jones, Eric Erslev, Scott Larson, Mark Hudson and Steven Holdaway
Paleomagnetic and structural evidence for oblique slip in a fault-related fold, Grayback Monocline, Colorado
Geological Society of America Bulletin (August 2008) 120 (7-8): 877-892


Significant fold-axis-parallel slip is accommodated in the folded strata of the Grayback monocline, northeastern Front Range, Colorado, without visible large strike-slip displacement on the fold surface. In many cases, oblique-slip deformation is partitioned; fold-axis-normal slip is accommodated within folds, and fold-axis-parallel slip is resolved onto adjacent strike-slip faults. Unlike partitioning strike-parallel slip onto adjacent strike-slip faults, fold-axis-parallel slip has deformed the forelimb of the Grayback monocline. Mean compressive paleostress orientations in the forelimb are deflected 15 degrees -37 degrees clockwise from the regional paleostress orientation of the northeastern Front Range. Paleomagnetic directions from the Permian Ingleside Formation in the forelimb are rotated 16 degrees -42 degrees clockwise about a bedding-normal axis relative to the North American Permian reference direction. The paleostress and paleomagnetic rotations increase with the bedding dip angle and decrease along strike toward the fold tip. These measurements allow for 50-120 m of fold-axis-parallel slip within the forelimb, depending on the kinematics of strike-slip shear. This resolved horizontal slip is nearly equal in magnitude to the approximately 180 m vertical throw across the fold. For 200 m of oblique-slip displacement (120 m of strike slip and 180 m of reverse slip), the true shortening direction across the fold is N90 degrees E, indistinguishable from the regionally inferred direction of N90 degrees E and quite different from the S53 degrees E fold-normal direction. Recognition of this deformational style means that significant amounts of strike slip can be accommodated within folds without axis-parallel surficial faulting.

ISSN: 0016-7606
EISSN: 1943-2674
Serial Title: Geological Society of America Bulletin
Serial Volume: 120
Serial Issue: 7-8
Title: Paleomagnetic and structural evidence for oblique slip in a fault-related fold, Grayback Monocline, Colorado
Affiliation: University of New Mexico, Department of Earth and Planetary Sciences, Albuquerque, NM, United States
Pages: 877-892
Published: 200808
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 59
Accession Number: 2008-104167
Categories: Structural geologyStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., 3 tables, geol. sketch map
N40°45'00" - N40°49'60", W105°16'60" - W105°10'00"
Secondary Affiliation: University of Colorado, USA, United StatesColorado State University, USA, United StatesU. S. Geological Survey, USA, United StatesChevron USA Production Company, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200836
Program Name: USGSOPNon-USGS publications with USGS authors
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