Pre-Late Cretaceous/Early Tertiary motion of the Osburn Fault, Coeur d'Alene mining district, Idaho

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5100338

Hayden, T J; Reid, R R ^[1]

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1. Univ. of Idaho, Moscow, ID (United States). Dept. of Geology and Geological Engineering

The Osburn Fault is a west-northwest-trending strike-slip fault (of Laramide or younger age with 26 km of dextral offset) parallel/subparallel to and near the center of the Lewis and Clark line (a zone of west- and northwest-trending high-angle faults extending from northern Idaho into western Montana). Initial fault movement in the Lewis and Clark line occurred during Middle Proterozoic time, with hypotheses for both right- and left-lateral motion having been put forth. In the Coeur d'Alene mining district, (bisected by the Osburn fault) research suggests faulting occurred pre-Osburn, while rocks were in ductile, ductile-brittle transition, and brittle regimes. The Osburn exhibits fractures, gouge, and striae indicative of movement in the brittle regime. North of, nearly parallel, and adjacent the Osburn, a 5 km wide mylonitic zone exhibits oblique-slip. Mylonite is also present south of the Osburn, as is a zone of annealed breccia (ductile-brittle transition), suggesting faulting occurred pre-Osburn, while the rocks were in the ductile and transitional regimes. Slickenlines north and south of the Osburn display a diversity of trends, generally exhibit moderate to steep plunges, with few slickenlines being parallel or subparallel the Osburn fault. These slickenlines suggest: brittle fault movement prior to the right-lateral motion of the Osburn fault; right-lateral motion along Osburn is a relatively young, brittle structural feature; and deformation related to strike-slip movement of the Osburn restricted to a narrow zone adjacent the fault.

• OSTI ID: 5100338
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

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