Geologic units in Portage county, Wisconsin

Additional scientific data in this geographic area

Wolf River batholith; Red River Granite (Middle Proterozoic) at surface, covers 28 % of this area

Contains alkali feldspar phenocrysts (0.5-2 cm), subordinate plagioclase and quartz, and rare clusters of biotite with or without hornblende

Cambrian, undivided (Cambrian) at surface, covers 19 % of this area

Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations

Gneiss, migmatite, and amphibolite (Late Archean) at surface, covers 14 % of this area

Quartzofeldspathic gneiss and less abundant amphibolite and migmatite. Includes granitoid rocks. Granitic gneiss at Port Edwards, WI on Wisconsin River has a U-Pb zircon age of 2870 +/- 13 Ma, and gneiss at Jim Falls in Chippewa River valley has a U-Pb zircon age of 2522 +/- 22 Ma (Sims and others, 1989)

Milladore Volcanic Complex (Early Proterozoic) at surface, covers 10 % of this area

Succession of poorly exposed interlayered metavolcanic and metasedimentary rocks. Lithic units described in Sims (1990)

Rhyolite (Early Proterozoic) at surface, covers 8 % of this area

Ash-flow tuffs and interbedded volcaniclastic sedimentary rocks and cogenetic granite (unit Xga) exposed as inliers in southern Wisconsin. In central Wisconsin pink, flow-banded rhyolite and chert-cemented breccia inferred to be 1760 Ma.

Granitic rocks, undivided (Early Proterozoic) at surface, covers 6 % of this area

Gray, weakly foliated to massive granite in poorly exposed areas.

Wolf River batholith; Wolf River Granite (Middle Proterozoic) at surface, covers 6 % of this area

Red, coarse-grained rapakivi granite consisting of large (1-3 cm) ovoid alkali feldspar sporadically mantled by plagioclase, interstitial plagioclase, quartz, biotite, hornblende, and ilmenite

Prairie du Chien Group (Ordovician) at surface, covers 4 % of this area

Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations

Fault rocks (Archean to Early Proterozoic) at surface, covers 2 % of this area

Mylonitic rocks of uncertain lithology in Eau Pleine shear zone

Wolf River Batholith; Anorthosite (Middle Proterozoic) at surface, covers 1 % of this area

Gray, coarse-grained (1-20 cm) plagioclase-rich (An45-53) rock containing interstitial orthopyroxene, clinopyroxene, Fe-Ti oxides, and apatite.

Wolf River batholith; Waupaca Granite (Middle Proterozoic) at surface, covers 1 % of this area

Rapakivi granite (wiborgite) containing 70-80 percent coarse (1.5 -5 cm) ovoid alkali feldspars mantled by plagioclase, coarse anhedral quartz, and interstitial hornblende and biotite

Granodiorite-tonalite (Early Proterozoic) at surface, covers < 0.1 % of this area

Gray, medium-grained intrusive rocks, including intrusion breccias. Exposed in central Wisconsin. Zircon ages range from 1837 to 1847 Ma