Pre-Upper Jurassic gneiss

Biotite, quartz diorite, trondhjemite, and hornblende gneisses, many of which are migmatitic; includes small granitic bodies locally. Small areas of mica schist, marble, amphibolite, and lime-silicate rocks in Entiat Mountains area of Chelan County.
State Washington
Name Pre-Upper Jurassic gneiss
Geologic age Mostly Cretaceous
Lithologic constituents
Major
Metamorphic > Gneiss
Incidental
Metamorphic > Migmatite
Metamorphic > Metasedimentary > Metacarbonate > Marble
Metamorphic > Metasedimentary > Metaclastic > Quartzite
Metamorphic > Schist (Greenschist)
Igneous > Plutonic > Granitic (Dike or sill)
Metamorphic > Metasedimentary > Metaclastic > Phyllite
Metamorphic > Amphibolite
Comments Skagit gneiss is primarily biotite gneiss with some hornblende gneiss; Methow gneiss is entirely biotite gneiss with some retrogression to schist at fault contacts (Barksdale, 1975). Skagit gneiss ranges from the staurolite-kyanite zone to sillimanite grade (Misch, 1977). Granitic plugs and dikes (of Skagit gneiss) are Tertiary in age (Stoffel and others, 1991); all metamorphic rocks are no younger than Cretaceous in age. This unit may also include paragneiss. The Chiwaukum Schist is a Barrovian sequence of metasedimentary rocks and some metavolcanic rocks (Duggan and Brown, 1994).
Stratigraphic units Methow gneiss; Skagit gneiss (may also be referred to as Custer Granite Gneiss); Eldorado Orthogneiss; Gabriel Peak Orthogneiss; Tonga Formation (in part); Swakane Biotite Gneiss; Chiwaukum Schist (in part); Napeequa Schist
References

Huntting, M.T., Bennett, W.A.G., Livingston, V.E.Jr., and Moen, W.S., 1961, Geologic Map of Washington: Washington Division of Mines and Geology, scale 1:500,000.

Stoffel, K.L., Joseph, N.L., Waggoner, S.Z., Gulick, C.W., Korosec, M.A., Bunning, B.B., 1991, Geologic Map of Washington--Northeast Quadrant: Washington Division of Geology and Earth Resources Geologic Map, GM-39, scale 1:250,000.

Cater, F.W. and Wright, T.L., 1967, Geologic Map of the Lucerne Quadrangle, Chelan County, Washington: U. S. Geological Survey Geologic Quadrangle Map GQ-647, scale 1:62,500.

Cater, F.W. and Crowder, D.F., 1967, Geologic Map of the Holden Quadrangle, Snohomish and Chelan Counties, Washington: U. S. Geological Survey Geologic Quadrangle Map GQ-646, scale 1:62,500.

Misch, P., 1977, Bedrock Geology of the North Cascades, in Brown, E. H. and Ellis, R. C. (eds.), Geological Excursions in the Pacific Northwest, Geological Society of America 1977 Annual Meeting, Seattle: Western Washington University, p. 1-62.

Tabor, R.W., Frizzell, V.A.,Jr., Booth, D.B., Waitt, R.B., Whetten, J.T., Zartman, R.E., 1993, Geologic Map of the Skykomish River 30- by 60-Minute Quadrangle, Washington: U. S. Geological Survey Miscellaneous Investigations Series Map I-1963, scale 1:100,000.

Tabor, R.W., Frizzell, V.A.,Jr., Whetten, J.T., Waitt, R.B., Swanson, D.A., Byerly, G.R., Booth, D.B., Hetherington, M.J., Zartman, R.E., 1987, Geologic Map of the Chelan 30-Minute by 60-Minute Quadrangle, Washington: U. S. Geological Survey Miscellaneous Investigations Series Map I-1661, scale 1:100,000.

Adams, J.B., 1964, Origin of the Black Peak Quartz Diorite, Northern Cascades, Washington: American Journal of Science, v. 262, no. 3, p. 290-306.

Dragovich, J.D., Logan, R.L., Schasse, H.W., Walsh, T.J., Lingley, W.S., Jr., Norman, D.K., Gerstel, W.J., Lapen, T.J., Schuster, J.E., Meyers, K.D., 2002, Geologic Map of Washington-Northwest Quadrant: Washington Division of Geology and Earth Resources Geologic Map GM-50, scale 1:250,000.

Duggan, K.M. and Brown, E.H., 1994, Correlation of the Tonga Formation and Chiwaukum Schist, North Cascades, Washington: Implications for Late Cretaceous orogenic mechanisms: Tectonics, v. 13, no. 6, p. 1411-1424.

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Counties Chelan - Douglas - King - Kittitas - Okanogan - Skagit - Snohomish - Whatcom