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WINDOUS BUTTE TUFF

Type Section Information

The Windous Butte Tuff has a type locality about 1 mile south of Windous Butte in Sec. 12, T. 12 N., R. 60 E. and Sec. 7, T. 12 N., R. 61 E., in White River Valley (Cook, 1965). As originally defined, the Windous Butte included nearly identical tuffs now designated the Pancake Summit Tuff based upon whole- rock geochemistry, radiometric dating, and paleomagnetic data (Gromme and others, 1972).

Geologic Age

The Windous Butte Tuff has been dated as Oligocene (30.4 Ma) by Blake and others (1969).

General Lithology

The Windous Butte Tuff is composed of two rhyolitic moderately to highly welded, crystal-rich ash-flow sheets with 20 to 50 percent phenocrysts. Crystals of quartz, feldspar and biotite compose about 40 percent of the rock (Cook, 1965). The upper ignimbrite is composed of about 100 to 300 feet of moderately welded, pale purple to grayish orange, crystal tuff which has a mottled texture. The lower ignimbrite is about 100 feet of highly welded, pale purple, crystal-vitric tuff, underlain by black porphyritic glass. The lower ignimbrite contains about 55 percent phenocrysts of angular smoky quartz and biotite in a devitrified glassy matrix (Cook, 1965). The lower portion of the Windous Butte is rhyolitic in composition and grades upward into quartz latitic tuffs (Kleinhampl and Ziony, 1985).

In the southern Pancake Range, the Windous Butte is a series of red to light-gray, welded and nonwelded, crystal vitric tuffs, often with pronounced columnar jointing and a dense 50-foot thick vitrophyre (Scott, 1969). Quartz and sanidine make up about 65 percent of the phenocrysts, 25 percent are plagioclase, and 10 percent are biotite. In the Pancake Range, the Windous Butte is commonly overlain by the Monotony Tuff.

In the White Pine Range, the Windous Butte is a crystal-rich quartz latite ignimbrite with about 10 percent quartz, 30 percent sanidine, 10 percent plagioclase, 7 percent biotite, 5 percent hornblende and 5 percent opaques, with 35 percent of the rock composed of glassy groundmass (Wire, 1961).

Average Thickness

Gromme and others (1972) report that the average thickness of the Windous Butte Formation is about 490 feet. Thickness estimates of Cook (1965) are not accurate because of the inclusion of the Pancake Summit Tuff in several localities. Hose and Blake (1976) estimated the unit is about 200 feet thick at its type section, and believed that most sections in White Pine County are between 100 and 200 feet thick. The Windous Butte is about 100 feet thick near Portuguese Mountain in the Pancake Range, and reaches a thickness of several hundred feet near Moody Peak according to Kleinhampl and Ziony (1985). In the southern Pancake Range, Scott (1969) estimated a thickness of about 800 feet. The thickest section of the Windous Butte is exposed within the Park Range in northern Nye County, where it is 1,800 feet thick (Kleinhampl and Ziony, 1985). It reaches a wedge edge in the Monitor Range where it is only 200 feet thick.

Areal Distribution

The Windous Butte Formation is present in the northern Hot Creek, Park, Monitor, Pancake, southern White Pine, northern Grant, and southern Egan Ranges. Gromme and others (1972) estimated that the unit has a maximum lateral extent of about 150 km in an east-west direction, and that it covers an area of about 8,200 square kilometers with a volume of 1,300 cubic kilometers. The Windous Butte was erupted from an immense caldron complex centered in the Hot Creek Valley region (Ekren and others, 1973).


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Last modified: 09/12/06