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Pre-Belt gneiss, schist, and related rocks

Pre-Belt gneiss, schist, and related rocks: comprises all the rocks older than the Belt series except the Stillwater complex. These include the Cherry Creek group, consisting of interlaminated gneiss, schist, marble, and quartzite; and the Pony series of Tansley and others, consisting of gneiss and schist of both sedimentary and igneous origin. Recent work has resulted in the distinction of small masses of granitic and injected rocks now regarded as resulting from intrusion in Cretaceous or Tertiary time. Other such masses may have escaped recognition.
StateMontana
NamePre-Belt gneiss, schist, and related rocks
Geologic ageArchean Proterozoic(?) preCambrian-Proterozoic(?) preCambrian(?) Phanerozoic | Paleozoic(?) Mesozoic(?) Cenozoic | Cambrian(?) Ordovician(?) Silurian(?) Devonian(?) Carboniferous(?) Permian(?) Triassic(?) Jurassic(?) Cretaceous(?) Tertiary
Original map labelpCgs
CommentsThis very broadly lumped map unit consists of a wide, wide range of metamorphic and igneous rocks. The metamorphic rocks range from greenschist-facies metasedimentary rocks up to granulite-facies gneisses, and almost every type of metamorphic lithology and grade in between. Most of the metamorphic rocks are Archean in age, but more recent studies and geologic mapping have shown several of these terranes are actually Proterozoic in age. The igneous rocks, not shown separately, are mainly Archean in age, but the mapped area also includes numerous cross cutting Cretaceous and Tertiary intrusives. The igneous rocks run the spectrum, mainly felsic in character, but including many mafic and ultramafic bodies. The intrusives come in all forms, from plutons to dikes and sills. Attribution of individual polygons from larger-scale maps is necessary to properly code these basement rocks of Montana.
Primary rock typemetamorphic rock
Secondary rock typeplutonic rock (phaneritic)
Other rock types
Lithologic constituents
Major
MetamorphicThis very broadly lumped map unit consists of a wide, wide range of metamorphic and igneous rocks. The metamorphic rocks range from greenschist-facies metasedimentary rocks up to granulite-facies gneisses, and almost every type of metamorphic lithology and grade in between. Most of the metamorphic rocks are Archean in age, but more recent studies and geologic mapping have shown several of these terranes are actually Proterozoic in age. The igneous rocks, not shown separately, are mainly Archean in age, but the mapped area also includes numerous cross cutting Cretaceous and Tertiary intrusives. The igneous rocks run the spectrum, mainly felsic in character, but including many mafic and ultramafic bodies. The intrusives come in all forms, from plutons to dikes and sills. Attribution of individual polygons from larger-scale maps is necessary to properly code these basement rocks of Montana.
Minor
Igneous > PlutonicThis very broadly lumped map unit consists of a wide, wide range of metamorphic and igneous rocks. The metamorphic rocks range from greenschist-facies metasedimentary rocks up to granulite-facies gneisses, and almost every type of metamorphic lithology and grade in between. Most of the metamorphic rocks are Archean in age, but more recent studies and geologic mapping have shown several of these terranes are actually Proterozoic in age. The igneous rocks, not shown separately, are mainly Archean in age, but the mapped area also includes numerous cross cutting Cretaceous and Tertiary intrusives. The igneous rocks run the spectrum, mainly felsic in character, but including many mafic and ultramafic bodies. The intrusives come in all forms, from plutons to dikes and sills. Attribution of individual polygons from larger-scale maps is necessary to properly code these basement rocks of Montana.
Map references
Ross, P.R., Andrews, D.A., and Witkind, I.J., 1955, Geologic map of Montana: U.S. Geological Survey, 2 sheets, scale 1:500,000.
Unit references
Van Gosen, B.S., Elliott, J.E., LaRock, E.J., du Bray, E.A., Carlson, R.R., and Zientek, M.L., 2000, Generalized geologic map of the Absaroka-Beartooth study area, south-central Montana: U.S. Geological Survey Miscellaneous Field Studies Map MF-2338, sca
Ruppel, E.T., O'Neill, J.M., and Lopez, D.A., 1993, Geologic map of the Dillon 1o x 2o quadrangle, Idaho and Montana: U.S. Geological Survey Miscellaneous Investigations Series Map I-1803-H, scale 1:250,000.
Ruppel, E.T., 1998, Geologic map of the eastern part of the Leadore 30' x 60' quadrangle, Montana and Idaho: Montana Bureau of Mines and Geology Open File Report 372, 9 p., scale 1:100,000.
Vitaliano, C.J., and Cordua, W.S., 1979, Geologic map of southern Tobacco Root Mountains, Madison County, Montana: Geological Society of America Map and Chart Series Map MC-31, scale 1:62,500.
Richards, P.W., 1957, Geology of the area east and southeast of Livingston, Park County, Montana: U.S. Geological Survey Bulletin 1021-L, p. 385-438.
Wilson, A.B., and Elliott, J.E., 1997, Geologic maps of western and northern parts of Gallatin National Forest, south-central Montana: U.S. Geological Survey Geologic Investigations Series Map I-2584, 2 sheets, scale 1:126,720.
Wulf, G.R., 1962, Lower Cretaceous Albian rocks in northern Great Plains: American Association of Petroleum Geologists Bulletin, v. 46, no. 8, p. 1371-141.
Blackstone, D.L., Jr., 1975, Geology of the East Pryor Mountain quadrangle, Carbon County, Montana: Montana Bureau of Mines and Geology Special Publication 69, 13 p., 1 plate, scale 1:24,000.
Kellogg, K.S., and Williams, V.S., 2000, Geologic map of the Ennis 30' x 60' quadrangle, Madison and Gallatin Counties, Montana, Park County, Wyoming: U.S. Geological Survey Miscellaneous Geologic Investigations Series Map I-2690, scale 1:100,000.
Lonn, J., 2000, Geologic map of the Lima 30' x 60' quadrangle, southwest Montana: Montana Bureau of Mines and Geology Open File Report 408, 12 p., scale 1:100,000.
Keefer, W.R., 1972, Geologic of the west half of the Neihart 15-minute quadrangle, central Montana: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-726, scale 1:62,500.
O'Neill, J.M., Klepper, M.R., Smedes, H.W., Hanneman, D.L., Frazer, G.D., and Mehnert, H.H., 1996, Geologic map and cross sections of the central and southern Highland Mountains, southwestern, Montana: U.S. Geological Survey Miscellaneous Geologic Invest
Vuke, S.M., Berg, R.B., Lonn, J.D., and Kellogg, K.S., 1995, Geologic map of the Bozeman 30' x 60' quadrangle, Montana: Montana Bureau of Mines and Geology Open File Report 334, 2 p., scale 1:100,000.
Sholes, B.C., 1984, Bibliography of geologic mapping for the Bozeman 1° x 2° quadrangle, south-central Montana: Montana Bureau of Mines and Geology Open File Report 135, scale 1:250,000.
Geographic coverageBeaverhead - Big Horn - Blaine - Carbon - Cascade - Deer Lodge - Gallatin - Judith Basin - Madison - Meagher - Park - Phillips - Silver Bow - Stillwater - Sweet Grass

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