Geologic units in Rusk county, Wisconsin

Mafic metavolcanic rocks (Early Proterozoic) at surface, covers 33 % of this area

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.

Cambrian, undivided (Cambrian) at surface, covers 29 % of this area

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

Granite-tonalite (Early Proterozoic) at surface, covers 12 % of this area

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

Barron Quartzite (Early Proterozoic) at surface, covers 12 % of this area

Pink to maroon to light-gray, medium-grained, moderately sorted quartzite. Red argillite (pipestone) interbedded locally. At least 213 m thick

Felsic volcanic and volcanogenic rocks (Early Proterozoic) at surface, covers 7 % of this area

Tuff, argillite, graywacke, and minor volcanic rocks of lower greenschist-facies in southern Rusk County. Could be younger in age than adjacent metavolcanic rocks.

Mafic to felsic metavolcanic rocks (Early Proterozoic) at surface, covers 6 % of this area

Volcanic rocks in areas of sparse geologic data and nondefinitive magnetic and gravity data

Metagabbro (Early Proterozoic) at surface, covers 0.3 % of this area

Mafic to ultramafic bodies defined and delineated principally by positive magnetic and gravity anomalies; includes diorite bodies. Comagmatic with unit Xmi

Quartzite (Early Proterozoic) at surface, covers 0.2 % of this area

Maroon but locally white, gray, and red quartzite (quartz arenite) with a basal quartzose conglomerate. At Flambeau Ridge (Chippewa County) consists of conglomerate. Distinguished from other quartzite units in being strongly deformed and metamorphosed. Includes Flambeau, Rib Mountain, McCaslin, and Thunder Mountain Quartzites of local usage