Mafic intrusions (Oligocene)

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 (Oligocene)
Geologic age Oligocene
Primary rock type gabbro
Secondary rock type granitoid
Other rock types
Lithologic constituents
Major
Igneous > Plutonic > Gabbroic > Gabbro (Dike or sill)
Minor
Igneous > Plutonic > Granitic (Dike or sill)
Map references
Walker, G.W. and MacLeod, N.S., 1991, Geologic map of Oregon: U.S. Geological Survey, scale 1:500,000.
Unit 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.
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.
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.
Counties Benton - Clatsop - Douglas - Lane - Lincoln - Marion - Polk - Tillamook - Washington - Yamhill