Imbrication and duplex development in the Absaroka thrust sheet, Haystack Peak area, Salt River Range, Wyoming

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5881791

Chester, J S ^[1]

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1. Saint Louis Univ., St. Louis, MO (United States)

The thrust sheet consists of three structural domains bounded by evenly spaced, major imbricate thrust faults, referred to in ascending order as the Sherman, Star and Stewart thrust faults. Significant variations in structural style between and within domains reflect magnitude of shortening, stacking order of structural lithic units, proximity to the basal Absaroka thrust surface, and position within the thrust sheet. The Paleozoic section comprising the sheet forms two main structural lithic units. The boundary between these units occurs near the contact of the Ordovician Bighorn and Devonian Darby formations. In the easternmost and structurally lowest domain where only the upper structural lithic unit is present, shortening was achieved by imbricate fan development. In domains where both structural lithic units are present, large magnitude shortening was achieved by duplex development in the lower unit and large amplitude, long wavelength folding in the upper unit. Two duplex systems have been identified, a passive roof duplex associated with the Steward thrust and an overlapping ramp-anticline associated with the Star thrust. Field observations and mechanical model results suggest that the main imbricate faults formed in a break-back sequence as the thrust sheet passed up and over a major dip ramp in the Absaroka thrust fault just west of the study area. Individual duplexes appear to have formed in a break-forward sequence. The structures may record a change in the mode of deformation of the Absaroka thrust sheet from translation along the Absaroka thrust fault and overlapping ramp anticline system to localized and intense shortening by tectonic wedging with the passive roof duplex. Such a change could reflect an increase in the ratio of the resistance to forward translation of the hanging wall relative to internal hanging wall strength during late stages of motion on the Absaroka thrust fault.

• OSTI ID: 5881791
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

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