Hypabyssal intrusive rocks

Hypabyssal, medium-grained, hornblende diorite and quartz diorite in small stocks and large dikes; includes intrusions of medium- to fine-grained gabbro and plugs and small stocks of medium-grained, holocrystalline, olivine andesite. Also includes medium-grained, commonly porphyritic biotite quartz monzonite and leucocratic granodiorite. Many of these intrusive bodies are moderately to intensely propylitized, as are wallrocks they intrude; locally, along shears, the rocks also are sericitized. Potassium-argon ages on several of these shallow intrusions range from about 8 Ma to about 22 Ma (Wise, 1969; Bikerman, 1970; Sutter, 1978; Power and others, 1981a, b; Fiebelkorn and others, 1983)
State Oregon
Name Hypabyssal intrusive rocks
Geologic age Miocene
Lithologic constituents
Major
Igneous > Plutonic > Dioritic > Quartz-diorite (Stock or pipe, Dike or sill)
Igneous > Plutonic > Dioritic > Diorite (Stock or pipe, Dike or sill)
Incidental
Igneous > Plutonic > Granitic > Granodiorite (Stock or pipe, Dike or sill)
Igneous > Plutonic > Syenitic > Quartz-monzonite (Stock or pipe, Dike or sill)
Igneous > Plutonic > Gabbroic > Gabbro (Stock or pipe, Dike or sill)
Igneous > Hypabyssal > Mafic-hypabyssal > Hypabyssal-andesite (Stock or pipe, Dike or sill)
References

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

Wise, W.S., 1969, Geology and petrology of the Mount Hood area-a study of High Cascade volcanism: Geological Society of America Bulletin, v. 80, p. 969-1006.

Bikerman, M., 1970, K-Ar ages of Laurel Hill pluton and dike, Oregon: the Ore Bin, v. 32, p.211-215.

Sutter, J.F., 1978, K-Ar ages of Cenozoic volcanic rocks from the Oregon Cascades west of 121o 30': Isochron/West, no. 21, p. 15-21.

Power, S.G., Field, C.W., Armstrong, r.L., and Harakal, J.E., 1981a, K-Ar ages of plutonism and mineralization, western Cascades, Oregon and southern Washington: Isochron/West, no. 31, p. 27-29.

Power, S.G., Field, C.W., Armstrong, r.L., and Harakal, J.e., 1981a, K-Ar ages of plutonism and mineralization, western Cascades, Oregon and Washington; additional information: Isochron/West, no. 32, p. 3.

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 Clackamas - Douglas - Jackson - Lane - Linn - Marion