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Porcupine Volcanics

Porcupine Volcanics - Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks
State Wisconsin
Name Porcupine Volcanics
Geologic age Middle Proterozoic
Comments previously called the "unnamed formation", including on paper map of Sims (1992). The unit symbol on that map is "Yu". This has been replaced by the naming the unit, the Porcupine Volcanics, and using the symbol "Ypv" (Cannon and others, 1997). Unit description here is from the unit description of "Yu" on Sims (1992)
Primary rock type rhyolite
Secondary rock type basalt
Other rock types andesite; mixed clastic/volcanic
Lithologic constituents
Major
Igneous > Volcanic > Mafic-volcanic > Andesite (Flow)Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks
Minor
Igneous > Volcanic > Felsic-volcanic > Rhyolite (Flow)rhyolite
Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks
Incidental
Sedimentary > Clastic > Mixed-clastic > Sandstone-mudstone (Flow)Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks
Map references
Cannon, W.F., Kress, T.H., Sutphin, D.M., Morey, G.B., Meints, Joyce, and Barber-Delach, Robert, 1997, Digital Geologic Map and mineral deposits of the Lake Superior Region, Minnesota, Wisconsin, Michigan: USGS Open-File Report 97-455 (version 3, Nov. 1999), on-line only
Unit references
Cannon, W.F., Kress, T.H., Sutphin, D.M., Morey, G.B., Meints, Joyce, and Barber-Delach, Robert, 1997, Digital Geologic Map and mineral deposits of the Lake Superior Region, Minnesota, Wisconsin, Michigan: USGS Open-File Report 97-455 (version 3, Nov. 1999), on-line only
Zartman and others, 1997, U-Th-Pb zircon ages of some Keweenawan Supergroup rocks from the south shore of Lake Superior: Canadian Journal of Earth Sciences, v. 34, p. 549-561
Sims, P.K., 1992, Geologic map of Precambrian rocks, southern Lake Superior region, Wisconsin and northern Michigan: U.S. Geological Survey Miscellaneous Investigations Map I-2185, scale= 1:500,000
Counties Iron