Loon Lake quarries, Ashland Co., Wisconsin, USAi

Regional Level Types
Loon Lake quarries	Group of Quarries
Ashland Co.	County
Wisconsin	State
USA	Country

Age: Mesoproterozoic (1000 - 1600 Ma)

Stratigraphic Name: Mellen Complex

Description: Gabbro, anorthositic gabbro, gabbroic anorthosite-Coarse-grained, generally 80 to 90 percent plagioclase (An55 to An60), lesser clinopyroxene, orthopyroxene, and rare olivine. Plagioclase crystals commonly show preferred orientation.

Comments: Midcontinent rift province; intrusion; rift basin

Lithology: Major:: {gabbro},Minor:: {anorthositic gabbro,troctolite}

Reference: Cannon, W.F., L.G. Woodruff, S.W. Nicholson, C.A. Hedgman, and R.D. Barber-Delach. Digital Bedrock Geologic Map of the Ashland and Northern Part of the Ironwood 30' x 60' Quadrangles, Wisconsin and Michigan. U.S. Geological Survey Open-File Report 99-546. [162]

Age: Stenian (1000 - 1200 Ma)

Description: gabbro, anorthosite, granite, peridotite

Comments: This unit was originally called "gabbros of uncertain affinity" on the Sims (1992) map. Since that map was published, several of these bodies have been dated and appear to be of Keweenawan affinity. This unit includes gabbros and anorthosites in the Amnicon Intrusion, the Mellen complex, and the peridotiite at Upson, MI as well as individual bodies (the unexposed Clam Lake, Round Lake intrusions). These units are now known to be of Keweenawan affinity. The gabbro associated with the Mellen complex has been dated by U-Pb zircon dating yielding a date of 1102.0 +/- 2.8 Ma and the Mellen granite has a U-Pb zircon date of 1100.9 +/- 1.4 Ma (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). A rhyolite associated with the Amnicon pluton has a U-Pb zircon date of 1101.8 +/- 6.7 Ma (C. Isachsen, Univ. of Arizona, unpublished data, 2003) Original map source: Cannon, W.F., Kress, T.H., Sutphin, D.M., Morey, G.B., Meints, Joyce, and Barber-Delach, Robert, 1997, Digital Geologic Map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. 19

Lithology: Major:{gabbro}, Minor:{anorthosite,peridotite,granite}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Age: Mesoproterozoic (1000 - 1600 Ma)

Comments: Mid-Continent Rift

Lithology: Bimodal volcanic rocks

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]