Quesnellian (Anarchist) stratigraphy, back-folding, and timing of volcanism and graben formation in NE Washington
- Echo Bay Exploration, Inc., Republic, WA (United States)
The Cooke Mt. mining district near Rupublic, WA, was mapped at 1:1000. The district is located in the northeastern portion of the Republic graben and preserves upper Paleozoic rocks of the Quesnel terrane unconformably overlain by Tertiary volcanic and arkosic rocks of the Challis Sequence. The graben is between the Kettle and Okanogan metamorphic core complexes. The upper Paleozoic (Anarchist) rocks of the district of their Challis cover documented four features of regional significance: (1) Sedimentary structures face from cherts and greenstones of the Knob Hill Group (cf. Kobau and Palmer Mt. Formations) into sedimentary rocks of the Attwood Formation (cf. Spectacle Lake, Bullfrog Mt. Formations), and clasts of Knob Hill cherts and phyllites occur in an olistostromal units of the Attwood Formation. Previously, no stratigraphic relationship has been observed between the two groups although they are commonly juxtaposed and together constitute the Anarchist assemblage of Quesnelia. (2) A large, west-vergent fold is herein interpreted as a back-thrust feature related to the accretion of the Intermontane superterrane. Similar west-directed structures to the east have been described in the North American rocks of the Kootenay arc. (3) The fold is dismembered by the Lambert Creek detachment fault. Six km offset of mineralized marker horizons contained in the fold provide a pin on the detachment. (4) Synclinal deformation of the Challis rocks predates two generations of graben-bounding faults. The Lambert Creek detachment fault cuts the Challis rocks and offsets the older of the graben faults (Curlew Lake-Cooke Mountain fault) but is cut by the younger, present graben boundary, the Sherman fault.
- OSTI ID:
- 5126469
- Report Number(s):
- CONF-9305259-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 25:5; Conference: 89. annual meeting of the Cordilleran Section and the 46th annual meeting of the Rocky Mountain Section of the Geological Society of America (GSA), Reno, NV (United States), 19-21 May 1993; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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