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GEOREF RECORD

New interpretations of the Piney Creek Thrust and associated Granite Ridge tear fault, northeastern Bighorn Mountains, Wyoming

Donald S. Stone
New interpretations of the Piney Creek Thrust and associated Granite Ridge tear fault, northeastern Bighorn Mountains, Wyoming
Rocky Mountain Geology (2003) 38 (2): 205-235

Abstract

The northwest-striking, northeast-directed Piney Creek thrust on the northeastern flank of the Bighorn Mountains in north-central Wyoming is traditionally interpreted as abruptly terminated on the northwest by the transverse Granite Ridge fault zone (new name). The structure of the mountain front north of this fault generally has been described as an unfaulted monocline. However, seismic-reflection, gravity, and borehole data, and the requirement of reasonable shortening balance along the mountain front indicate subsurface continuity of the (buried) Piney Creek thrust northward from the Granite Ridge fault zone-perhaps to the Tongue River lineament near the Montana border. Based on these subsurface data, the Granite Ridge fault is described here as a true tear fault confined to the hanging wall of an uninterrupted, approximately 30 degrees -dipping Piney Creek thrust, segmenting hanging-wall thrust displacement between the Piney Creek block on the south and Walker Mountain block on the north. Slip on the Granite Ridge tear fault is expressed at the surface along the eastern margin of the Bighorn Mountains, west of Story, Wyoming, as a resequent fault-line scarp with approximately 2000 ft (600 m) of relief, and with approximately 3.3 mi ( approximately 5.3 km) of left separation of steeply dipping, Paleozoic rocks. Based on measurement between piercing points produced by the lines of intersection of the steeply, east-dipping Cambrian-Precambrian unconformity with the Piney Creek thrust surface along either side of the Granite Ridge tear fault, a (reverse) left-oblique slip of approximately 15,000 ft ( approximately 4500 m) is measured on this tear fault zone. Thus, 30,000 ft (9100 m) of net slip on the Piney Creek thrust in the Piney Creek block decreases to 15,000 ft (4500 m) of net slip in the Walker Mountain block, and slip on the thrust further declines northward. The described Granite Ridge tear fault-Piney Creek thrust geometry may provide a useful model in the investigation of similar fault-offset mountain fronts within the Laramide foreland province of the Middle Rocky Mountains.


ISSN: 1555-7332
EISSN: 1555-7340
Coden: WUGGAO
Serial Title: Rocky Mountain Geology
Serial Volume: 38
Serial Issue: 2
Title: New interpretations of the Piney Creek Thrust and associated Granite Ridge tear fault, northeastern Bighorn Mountains, Wyoming
Author(s): Stone, Donald S.
Affiliation: 6178 South Lakeview Street, Littleton, CO, United States
Pages: 205-235
Published: 2003
Text Language: English
Publisher: University of Wyoming, Dept. of Geology and Geophysics, Laramie, WY, United States
References: 80
Accession Number: 2004-038916
Categories: Structural geologyApplied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Includes appendix
Illustration Description: illus. incl. block diags., sects., strat. col., geol. sketch maps
N44°15'00" - N44°45'00", W107°30'00" - W106°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2018, American Geosciences Institute.
Update Code: 200411
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