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Geologic units in Sawyer county, Wisconsin
[Additional scientific data in this geographic area]
- Gabbroic rocks of Keweenawan affinity (Middle Proterozoic) at surface, covers 0.4 % of this area
Gabbroic rocks of Keweenawan affinity - gabbro, anorthosite, granite, peridotite
- Mafic metavolcanic rocks (Early Proterozoic) at surface, covers 19 % of this area
Mafic metavolcanic rocks - Dominantly tholeiitic basalt and basaltic andesite flows and tuffs; associated with sheet dikes, massive and layered metagabbro, and ultramafic rocks. In northeastern Wisconsin, rocks have been named the Quinnesec Formation.
- Chengwatana Volcanic Group (Middle Proterozoic) at surface, covers 5 % of this area
Chengwatana Volcanic Group - Gray basalt flows, interflow breccia, tuff, and minor sedimentary rocks
- Migmatitic gneiss and amphibolite (Late to Early Archean) (Archean) at surface, covers 18 % of this area
Migmatitic gneiss and amphibolite (Late to Early Archean) - Varied gneisses of mostly unknown age in cores of gneiss domes and fault-bounded uplifts (Archean gneiss terranes). Except for the Watersmeet dome (Late to Early Archean), all dated rocks are Late Archean. Includes granite of Late Archean age that transgresses gneisses and amphibolite.
- Barron Quartzite (Early Proterozoic) at surface, covers 8 % of this area
Barron Quartzite - Pink to maroon to light-gray, medium-grained, moderately sorted quartzite. Red argillite (pipestone) interbedded locally. At least 213 m thick
- Biotite schist (Early Proterozoic) at surface, covers 15 % of this area
Biotite schist - Metamorphosed graywacke in poorly exposed areas in northwestern Wisconsin. Sample at one locality (near Blockhouse Lake, 10 km northeast of Park Falls, T. 40 N., R. 1 E.) has a U-Pb zircon age of 1852 +/- 6 Ma (Sims and others, 1985b)
- Cambrian, undivided (Cambrian) at surface, covers 15 % of this area
Cambrian, undivided - Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations
- Granite-tonalite (Early Proterozoic) at surface, covers 16 % of this area
Granite-tonalite - Gray to pinkish-gray, medium-grained, generally equigranular granite to tonalite and granitoid gneiss; locally includes diorite. Intrudes older metavolcanic rocks. Zircon ages range from 1852 +/- 15 to 1862 +/- 5 Ma
- Gneiss and amphibolite (Late Archean, 2.640-2.750 Ma) (Late Archean) at surface, covers 1 % of this area
Gneiss and amphibolite (Late Archean, 2.640-2.750 Ma) - Interlayered quartzofeldspathic gneiss and amphibolite in Marenisco, Mich., area and northwestern Wisconsin. Protoliths are bimodal intermediate and mafic volcanic rocks (Sims and others, 1984).
- Granitic rocks of 1760-Ma age group (Early Proterozoic) at surface, covers 3 % of this area
Granitic rocks of 1760-Ma age group - In northern Wisconsin, granite to granodiorite of varied texture. In southern Wisconsin (not mapped separately), red to pink alkali-feldspar granophyric granite associated with rhyolites of both peraluminous and metaluminous affinities (unit Xr of Marshfield terrane).