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Mineral Resources > Online Spatial Data > Geology > by state > Minnesota Geology

Geologic units in Benton county, Minnesota

Migmatitic gneiss, amphibolite, and granite (Middle to Early Archean) at surface, covers 11 % of this area

Migmatitic gneiss, amphibolite, and granite - Montevideo and Morton Gneisses (3600-3000 m.y.) in the Minnesota River Valley, southwestern Minnesota; McGrath Gneiss (2750 m.y.) east of Mille Lacs Lake; components of Hillman Migmatite southwest of Mille Lacs Lake; and Sartell Gneiss in Stearns County. Inferred to include various younger rocks, including granitoid intrusions in the Hillman Migmatite and pillowed basalt in poorly exposed areas of southwestern Minnesota.

Lithology: gneiss; amphibolite; granite; basalt

Unnamed schistose, volcanic, and hypabyssal rocks of mafic composition and volcanic, volcaniclastic, and intrusive rocks of felsic composition (Early Proterozoic) at surface, covers 2 % of this area

Unnamed schistose, volcanic, and hypabyssal rocks of mafic composition and volcanic, volcaniclastic, and intrusive rocks of felsic composition - May be correlative with rocks of the Wisconsin magmatic terranes.

Lithology: schist; felsic volcanic rock; mafic volcanic rock

Little Falls Formation; Quartz-rich slate, argillite, and schist in the northwestward extent of the unit and coarse-grained megacrystic garnet-staurolite-schist in the southwestward extent (Early Proterozoic) at surface, covers 5 % of this area

Little Falls Formation; Quartz-rich slate, argillite, and schist in the northwestward extent of the unit and coarse-grained megacrystic garnet-staurolite-schist in the southwestward extent - Unit as an uncertain stratigraphic position relative to other Paleoproterozoic stratified units but is apparently younger than the Mille Lacs and North Range Groups.

Lithology: slate; argillite; schist

Late-tectonic intrusions of the Penokean orogen (Early Proterozoic) at surface, covers 82 % of this area

Late-tectonic intrusions of the Penokean orogen - Includes the St. Cloud and Rockville Granites and Reformatory granodiorite of east-central Minnesota, the Section 28 granite, the Cedar Mountain Complex, and other unnamed intrusions exposed along the Minnesota River Valley in southwestern Minnesota

Lithology: granite; granodiorite

Cretaceous rocks, undivided (Cretaceous) at surface, covers 0.5 % of this area

Cretaceous rocks, undivided - Dakota, Graneros, Greenhorn, Carlie, Niobara, and Pierre formations and their nonmarine equivalents in northwestern, southwestern, and southeastern Minnesota

Lithology: shale; sandstone; limestone