Oligocene intrusive rocks (TXOGi;0)

State	Texas
Name	Oligocene intrusive rocks
Geologic age	Phanerozoic \| Cenozoic \| Tertiary \| Oligocene
Original map label	Oi
Comments	stocks, laccoliths, sills, and dikes. Major rock types--basalt, hawaiite, mugearite, trachyte, quartz trachyte, rhyolite, phonolite, latite, trachyandesite, and their coarser grained equivalents. At Marble Canyon intrusive stock in Diablo Mtns, Culberson Co, 30 mi north of Van Horn, TX, (Price and Henry, 1986, p. 17), rocks are alkali gabbro, nepheline syenite dikes, quartz syenite at core of stock, also hybrid rock, numerous contact metamorphism and hydrothermal minerals reported. K-Ar ages about 33, 35, 36, 37, and 39.5 Ma (p. 22). Quitman-Sierra Blanca complex are caldera ring-dike intrusives and stocks: quartz monzonite, rhyolite, granite (laccolith). K-Ar age 33.9+-0.8 Ma (Shannon and Goodell, 1986).
Primary rock type	basalt
Secondary rock type	trachyte
Other rock types	felsic volcanic rock; rhyolite; phonolite; latite; trachyandesite
Lithologic constituents	Incidental Igneous > Plutonic > Granitic > Granite (Stock or pipe)
Map references	Bureau of Economic Geology, 1992, Geologic Map of Texas: University of Texas at Austin, Virgil E. Barnes, project supervisor, Hartmann, B.M. and Scranton, D.F., cartography, scale 1:500,000
Unit references	Price, J.G., and Henry, C.D., 1986, Geology of Marble Canyon in Price, J.G., Henry, C.D., Parker, D.F., and Barker, D.S., eds., Igneous geology of Trans-Pecos Texas, field trip guide and research articles: The University of Texas at Austin, Bureau of Eco Shannon, W.M. and Goodell, P.C., 1986, Lithochemistry of intrusive rocks of the Quitman-Sierra Balnce igneous complex, Hudspeth County, Texas in Price, J.G., Henry, C.D., Parker, D.F., and Barker, D.S., eds., Igneous geology of Trans-Pecos Texas, field t
Geographic coverage	Brewster - Culberson - El Paso - Hudspeth - Jeff Davis - Presidio