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Influence of Precambrian rock compositions and fabrics on the development of Rocky Mountain foreland folds

Ronald B. Chase, Christopher J. Schmidt and Paul W. Genovese
Influence of Precambrian rock compositions and fabrics on the development of Rocky Mountain foreland folds (in Laramide basement deformation in the Rocky Mountain foreland of the Western United States, Christopher J. Schmidt (editor), Ronald B. Chase (editor) and Eric A. Erslev (editor))
Special Paper - Geological Society of America (1993) 280: 45-72

Abstract

The distribution of Laramide strain in the Precambrian basement rocks of four small Rocky Mountain foreland folds was controlled by lithologies and orientations of preexisting foliation in the faulted forelimbs. Features of brittle deformation that developed in the basement were faults, sets of parallel, conjugate, or anastomosing fractures, zones of penetrative grain cracks and intergrain slip without grain-size reduction, and local zones of cataclasis or incipient mylonitization. In the London Hills anticline of Montana, foliation in amphibolite and gneiss was nearly parallel to bedding in cover rocks prior to folding. The foliation in the forelimb was rotated and deformed by layer-parallel slip between a forelimb thrust and a fault in a diabase dike located at the hinge zone of the anticline. In the Sheephead Mountain anticline of Wyoming, the forelimb fault cut foliation in quartzofeldspathic gneiss at a high angle. Penetrative brittle deformation occurred in the forelimb as a wide zone of fractures parallel to a forelimb thrust at the basement-cover contact, but the basement rocks were not folded. In the Gnat Hollow anticline-syncline, Colorado, foliation in interlayered granite, schist, and gneiss dipped about 20 degrees more steeply than the forelimb thrust. Brittle deformation was confined to the fault zone and a small region in the core of the forelimb anticline. In the Romero Hills anticline, New Mexico, foliation in the basement was parallel to thrusts that cut both basement and cover rocks. Slip on foliation surfaces near the thrusts was pervasive and simple shear on foliation was distributed across the backlimb and forelimb of the structure. In comparing the four structures, preexisting foliation surfaces were most active during Laramide deformation where they paralleled forelimb faults, and were least active where foliation was at a high angle to forelimb faults or was not rotated into the forelimb orientation. If the angle between faults and foliation is about 15 degrees or more, or if foliation is not nearly parallel to cover-rock layers, preexisting foliation appears to have exerted little influence on Laramide strain patterns in the foreland folds.


ISSN: 0072-1077
EISSN: 2331-219X
Coden: GSAPAZ
Serial Title: Special Paper - Geological Society of America
Serial Volume: 280
Title: Influence of Precambrian rock compositions and fabrics on the development of Rocky Mountain foreland folds
Title: Laramide basement deformation in the Rocky Mountain foreland of the Western United States
Author(s): Chase, Ronald B.Schmidt, Christopher J.Genovese, Paul W.
Author(s): Schmidt, Christopher J.editor
Author(s): Chase, Ronald B.editor
Author(s): Erslev, Eric A.editor
Affiliation: Western Michigan University, Department of Geology, Kalamazoo, MI, United States
Affiliation: Western Michigan University, Department of Geology, Kalamazoo, MI, United States
Pages: 45-72
Published: 1993
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
ISBN: 0-8137-2280-2
References: 34
Accession Number: 1993-046847
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., geol. sketch maps
N37°00'00" - N41°00'00", W109°00'00" - W102°00'00"
N44°30'00" - N49°00'00", W116°01'60" - W104°01'60"
N31°30'00" - N37°00'00", W109°04'60" - W103°00'00"
N41°00'00" - N45°00'00", W111°04'60" - W104°04'60"
Secondary Affiliation: Colorado State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 1993
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