Volcanic rocks in areas of sparse geologic data and nondefinitive magnetic and gravity data
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)
Mafic to ultramafic bodies defined and delineated principally by positive magnetic and gravity anomalies; includes diorite bodies. Comagmatic with unit Xmi
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
Interlayered quartzofeldpathic gneiss and amphibolite between Athens shear zone and Owen fault, central Wisconsin
Tuff, argillite, graywacke, and minor volcanic rocks of lower greenschist-facies in southern Rusk County. Could be younger in age than adjacent 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.