Felsic augen gneiss after porphyritic granite; Middle Proterozoic; southern Belt province (IDYifm;0)

State	Idaho
Name	Felsic augen gneiss after porphyritic granite; Middle Proterozoic; southern Belt province
Geologic age	Middle Proterozoic
Original map label	PCim; ;Ki; Tei
Comments	Yifm is felsic augen gneiss after two-mica granite with rapakivi texture. A large Yifm pluton in the northeastern part of the Salmon River Mountains has been dated 1364 +/- 9 Ma (ID025, ID167). It contains large oblate spheroidal microcline crystals with albitic rims (rapakivi texture) in a matrix of quartz and feldspar, with biotite and minor muscovite. This thick ring- or dish-shaped body of orthogneiss intrudes Middle Proterozoic metasedimentary rocks and amphibolitic mafic sills. It is intruded by globular masses of diabase, indicating that it is a product of bimodal mafic-felsic magmatism (ID164). AAB eliminated PCim by changing PCim polygons to Yifm.
Primary rock type	peraluminous granite
Secondary rock type	orthogneiss
Other rock types	diabase; amphibolite
Lithologic constituents	Major Metamorphic > Gneissorthogneiss with microcline augen Igneous > Plutonic > Granitic > Alkalli-feldspar-granite > Alkali-granite (Pluton)porphyritic two-mica granite with rapakivi texture Incidental Metamorphic > Amphibolite (Amphibolite)inclusions of amphibolite after mafic sills Igneous > Plutonic > Gabbroic (Diabase)globular masses of diabase (chilled gabbroic magma) in granite
Map references	Bond, J.G., Kauffman, J.D., Miller, D.A., and Venkatakrishnan, Ramesh, 1978, Geologic map of Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, with contributions from U.S. Geological Survey, scale 1:500,000.
Unit references	Bond, J.G., Kauffman, J.D., Miller, D.A., and Venkatakrishnan, Ramesh, 1978, Geologic map of Idaho: Moscow, Idaho, Idaho Bureau of Mines and Geology, with contributions from U.S. Geological Survey, scale 1:500,000. Evans, K.V. and Green, G.N., 2003, Geologic map of the Salmon National Forest and vicinity, east-central Idaho: U.S. Geological Survey Geological Investigations Series I-2765, scale 1:100,000 with pamphlet, 19 p. [http://pubs.er.usgs.gov/publication/i2765] Doughty, P.T., and Chamberlain, K.R., 1996, Salmon River Arch revisited: new evidence for 1370 Ma rifting near the end of deposition in the Middle Proterozoic Belt basin: Canadian Journal of Earth Sciences, v. 33, no. 7, p. 1037-1052. Evans, K.V., and Zartman, R.E., 1988, Early Paleozoic alkalic plutonism in east-central Idaho: Geological Society of America, v. 100, p. 1981-1987.
Geographic coverage	Idaho - Lemhi