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Mafic intrusions

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Sheets, sills, and dikes of massive granophyric ferrogabbro; some bodies strongly differentiated and include pegmatitic gabbro, ferrogranophyre, and granophyre (MacLeod, 1981). Plagioclase and amphibole from unit have yielded K-Ar ages of about 30 Ma (Snavely and others, 1976a)
State Oregon
Name Mafic intrusions
Geologic age Oligocene
Lithologic constituents
Major
Igneous > Plutonic > Gabbroic > Gabbro (Dike or sill)
Minor
Igneous > Plutonic > Granitic (Dike or sill)
References

Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.

Snavely, P.D., Jr., MacLeod, N.S., Wagner, H.C., and Rau, W.W., 1976a, Geologic map of the Cape Foulweather and Euchre Mountain quadrangles, Lincoln County, Oregon: U.S. Geological Survey Miscellaneous Investigations Series Map I-868, scale 1:62,500.

https://pubs.er.usgs.gov/publication/i868

Snavely, P.D., Jr., MacLeod, N.S., Wagner, H.C., and Rau, W.W., 1976c, Geologic map of the Waldport and Tidewater quadrangles, Lincoln, Lane, and Benton Counties, Oregon: U.S. Geological Survey Miscellaneous Investigations Series Map I-866, scale 1:62,500.

https://pubs.er.usgs.gov/publication/i866

Fiebelkorn, R.B., Walker, G.W., Macleod, N.S., McKee, E.H., and Smith, J.G., 1983, Index to K-Ar determinations for the State of Oregon: Isochron/West, no. 37, p. 3-60.
NGMDB product
Counties Benton - Clatsop - Douglas - Lane - Lincoln - Marion - Polk - Tillamook - Washington - Yamhill