Chapter 5: LaBarge Meadows cross-strike structural discontinuity and lateral ramping in the Absaroka thrust system
Published:January 01, 1992
Julian D. Fowles, Nicholas B. Woodward, 1992. "Chapter 5: LaBarge Meadows cross-strike structural discontinuity and lateral ramping in the Absaroka thrust system", Regional Geology of Eastern Idaho and Western Wyoming, Paul Karl Link, Mel A. Kuntz, Lucian B. Piatt
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Cross-strike structural discontinuities (CSDs) involve aligned reentrants and structural trend changes oblique to major thrust and fold belt orientations. The LaBarge Meadows area of the Absaroka thrust system is the western part of an area of such structural trend changes involving the Absaroka, Darby, and Prospect thrust systems. The Absaroka system structures have not been previously discussed in the context of CSDs, but their geometry and interpretation place major constraints on more eastern parts. The tear faults (northeast-southwest and east-west trending) that directly connect the Absaroka system with the Darby-Prospect structures are of minor and dominantly dip-slip displacement in the Absaroka sheet, despite their strike-slip separation. They overprint and merely complicate the recognition of the major Absaroka system structures, namely (1) a major (1,000 m) up-to-the-south lateral ramp from Cambrian to Pennsylvanian strata, and (2) a division of the single Absaroka thrust sheet into three subsidiary thrust sheets (Tunp, Commissary, and Absaroka sheets), which begins north of the CSD but becomes obvious south of it. The increase in thrust system complexity is progressive from north to south over 30 km. It coincides with gradual thickening in the Lower Mesozoic Structural Lithic Unit and gradual thinning of the Paleozoic structural lithic units. The lateral ramp and the changes in thrust spacing are both therefore inferred to be related to variations in the relevant stratigraphic intervals and not directly related to any basement structures.