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GEOREF RECORD

Laramide basement deformation in an evolving stress field, Bighorn Mountain front, Five Springs area, Wyoming

Donald U. Wise and Curtis M. Obi
Laramide basement deformation in an evolving stress field, Bighorn Mountain front, Five Springs area, Wyoming
AAPG Bulletin (October 1992) 76 (10): 1586-1600

Abstract

New road cuts of U.S. Route 14a along the western flank of the Bighorn Mountains of Wyoming create nearly continuous outcrops through the edge of a Laramide uplift. Exposed granitic basement in the range-front area is divided into three large, differentially rotated blocks separated by shattered, poorly exposed zones. Within each of these rotated blocks are three populations of faults: (1) an early set of dominantly strike-slip faults at high angles to the front with either polish or smearing of hematite, epidote, and/or chlorite, (2) a slightly younger set of faults with mostly similar motion and mineralization, but no smear or polish, and (3) a young set composed mostly of thrust faults marked by gouge and pervasive shattering. Stress tensor analysis on these three fault populations shows that maximum compressive stress (sigma 1) acted N25E-S25W, normal to the local range front, but changed plunge with time. In the early buckling stages, sigma 1 plunged at about 30 degrees in both directions away from the future buckle. Subsequently, sigma 1 assumed a relatively uniform 30 degrees plunge into the range, presumably as a result of reduced resistance to buckling. Finally, under extremely brittle conditions associated with regional uplift and erosion, sigma 1 assumed a relatively flat plunge through the rotating blocks. The exposures support models of basement "folding" by subhorizontally driven tectonic forces creating an early buckle zone that expanded into a small number of rotated blocks with subsequent, beanbag-like, minor reshaping of the rotating blocks by many small faults.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 76
Serial Issue: 10
Title: Laramide basement deformation in an evolving stress field, Bighorn Mountain front, Five Springs area, Wyoming
Affiliation: University of Massachusetts, Department of Geology and Geography, Amherst, MA, United States
Pages: 1586-1600
Published: 199210
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 47
Accession Number: 1992-042409
Categories: Structural geology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. block diags., sects., sketch maps
N44°00'00" - N46°00'00", W110°00'00" - W106°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute.
Update Code: 1992
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