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

Conference · Wed Jan 01 00:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5725260

Chase, R B; Schmidt, C J ^[1]; Genovese, P W ^[2]

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1. Western Michigan Univ., Kalamazoo, MI (United States). Dept. of Geology
2. Princeton Univ., NJ (United States). Dept. of Geophysical Sciences

The distribution of Laramide strain in the Precambrian basement rocks of four small Rocky Mountain foreland folds was controlled by lithologies and orientations of pre-existing foliation in the faulted forelimbs. Features of brittle deformation include faults, sets of parallel, conjugate, or anastomosing fractures, zones of penetrative grain cracking and intergrain slip without grain size reduction, and local zones of cataclasis or incipient mylonitization. In the London Hills anticline, Montana, foliation 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 hinge-controlling fault. In the Sheephead Mountain anticline, Wyoming, the forelimb fault cut foliation at a high angle. Penetrative brittle deformation occurred along a wide zone of fractures parallel to a forelimb thrust at the basement-cover contact. In the Gnat Hollow anticline, Colorado, foliation dipped about 20[degree] more steeply than the forelimb thrust. Brittle deformation was confined mainly to the fault zone. 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 in both the forelimb and backlimb. Pre-existing foliation surfaces were most active where they paralleled forelimb faults and 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 10[degree] [+-] or more, pre-existing foliation appears to have exerted little influence on Laramide strain patterns.

• OSTI ID: 5725260
• Report Number(s): CONF-921058-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
COLORADO
ROCKY MOUNTAINS
MONTANA
NEW MEXICO
GEOLOGIC STRUCTURES
WYOMING
BASEMENT ROCK
DEFORMATION
GEOCHEMISTRY
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
LITHOLOGY
ORIENTATION
ORIGIN
PRECAMBRIAN ERA
ROTATION
STRAINS
STRESS ANALYSIS
TECTONICS
CHEMISTRY
DEVELOPED COUNTRIES
GEOLOGIC AGES
GEOLOGY
MOTION
MOUNTAINS
NORTH AMERICA
PETROLOGY
USA
580000* - Geosciences