Oldest gneiss complex (WYUgn;0)

OLDEST GNEISS COMPLEX--Chiefly layered granitic gneiss, locally migmatitic. Local masses of quartzite, metagraywacke, iron-formation, and other metasedimentary rocks and amphibolite and felsic gneiss thought to be volcanic; metasedimentary rocks in Beartooth Mountains contain detrital zircon dated at more than 3,400 Ma. Inclusions show evidence of granulite-facies metamorphism prior to 2,800 Ma. Mueller and others (1982) suggest that large areas in Beartooth Mountains were invaded by Late Archean granite (age about 2,800 Ma). Bighorn Mountains--Dates of metamorphism 3,000+ Ma.

State	Wyoming
Name	Oldest gneiss complex
Geologic age	Archean
Original map label	Ugn
Primary rock type	granitic gneiss
Secondary rock type	migmatite
Other rock types	metamorphic rock
Lithologic constituents	Major Sedimentary > Chemical > Banded-iron-formation Metamorphic > Metasedimentary > Metaclastic > Metasandstone > Metagraywackemetagraywacke Metamorphic > Amphibolite Metamorphic > Metasedimentary > Metaclastic > Quartzite Metamorphic > Migmatite Metamorphic > Gneiss
Map references	Love, J.D. and Christiansen, Ann Coe, 1985, Geologic Map of Wyoming: U.S. Geological Survey. [http://pubs.er.usgs.gov/publication/ofr83802]
Unit references	Love, J.D. and Christiansen, Ann Coe, 1985, Geologic Map of Wyoming: U.S. Geological Survey. [http://pubs.er.usgs.gov/publication/ofr83802]
Geographic coverage	Big Horn - Fremont - Hot Springs - Johnson - Natrona - Park - Sublette - Washakie