Porcupine Volcanics (MIYpv;0)

State	Michigan
Name	Porcupine Volcanics
Geologic age	Middle Proterozoic
Original map label	Ypv
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 This has been replaced by the naming the unit, the Porcupine Volcanics, and using the symbol "Ypv" as was done in the digital map of Cannon et al. (1997). Unit description here is from the unit description of "Yu" on Sims (1992)
Primary rock type	basalt
Secondary rock type	andesite
Other rock types	rhyolite; medium-grained mixed clastic
Lithologic constituents	Major Igneous > Volcanic > Mafic-volcanic > Basalt (Flow)Generally dark-gray basalt, andesite, and felsite flows and subordinate interflow sedimentary rocks 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 Incidental Sedimentary > Clastic > Mixed-clastic (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	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 [http://pubs.er.usgs.gov/publication/i2185]
Geographic coverage	Gogebic - Ontonagon