AN  INTEGRATED PETROLEUM  EVALUATION OF NORTHEASTERN  NEVADA


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QUATERNARY-TERTIARY BASALT FLOWS AND BRECCIAS

Pliocene and Pleistocene basalt flows, cinder and ash are perhaps best displayed in the widespread volcanic field exposed in the Lunar Crater area of the southern Pancake Range in northern Nye County. Fresh cones are commonly a composite of ash, cinder and block ejecta and flows (Kleinhampl and Ziony, 1985; Scott and Trask, 1971). The flows are commonly about 100 feet thick and are composed of vesicular and porphyritic alkaline basalts with phenocrysts up to several centimeters across of olivine, plagioclase, pyroxene, and in the younger flows xenoliths of dunite, peridotite, and gabbro, in a fine-grained to aphanitic groundmass (Scott, 1969; Kleinhampl and Ziony, 1985). Individual flows are not areally extensive and can commonly be traced to nearby sources (Scott, 1969). Similar black to gray porphyritic basalts with 1 to 2 cm phenocrysts of labradorite are present in the southern Pancake and northern Reveille Ranges where they reach thickness of 200 feet. These flows contain 1 to 2 cm phenocrysts of labradorite and give whole rock ages of 5.7 +/- 0.2 Ma (Ekren and others, 1973).

North of the Lunar Crater field similar basalts and dikes are exposed in the Moores Station Quadrangle portion of the southern Pancake Range. Along Basalt Butte up to 100 feet of gray porphyritic basalt containing phenocrysts of labradorite up to 1 cm across and forsterite up to 3 mm across, are floating in a groundmass of plagioclase laths, interstitial clinopyroxene, opaque minerals, and sparse olivine (Ekren and others, 1973). These flows are dated at 10.2 +/- 0.9 Ma (Ekren and others, 1973).


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Last modified: 09/12/06