Tertiary Volcanic Center, West-Central Nevada

摘要

The Clan Alpine Mountains, Churchill County, Nevada, contain two sequences of Tertiary rhyolite tuffs and flows which are contemporaneous but markedly different in structure and thickness. The sequence in the northern part of the range consists of about 500 m of well-stratified ash-flow sheets of age range 22 to 30 m.y. The southern part of the range contains an assemblage of lava flows, domes, and ash-flow and epiclastic tuff beds which is here subdivided into five mappable units. Radiometric ages are 22 to 30 m.y. Based on gravimetric analysis, the thickness of the southern sequence is at least 3,000 m and perhaps 5,000 m. The contact of the two rhyolite sequences, which is now largely eroded, was probably an abrupt gradation close to the present northern margin of the southern sequence. Structural evidence indicates that the voluminous eruptions of the southern sequence were probably from local sources and were concurrent with faulting such that the rocks were deposited in one or more volcano-tectonic depressions. Recognition of the north wall of at least one caldera within the southern sequence seems clear. Age relations indicate that the vents for the southern sequence were probably the source of at least some of the ash flows of the northern sequence. Similar age and structural relations between different sequences of rhyolite tuffs and flows in the next range east, the Desatoya Mountains, suggest that the volcano-tectonic feature of which the southern sequence is a part extended east of the Clan Alpine Mountains.