Mount Belknap and Red Hills calderas and associated rocks, Marysvale volcanic field, west-central Utah

Field guide to geologic excursions in southwestern Utah and adjacent areas of Arizona and Nevada

“…Dated by Best and others (1980) at 500,000 years old. Capping the Tushar Mountains to our right is the Mount Belknap caldera, part of the bimodal sequence with an age of about 20 Ma (Cunningham and Steven, 1979a). …”

“…We will visit its source caldera, the Monroe Peak caldera, shortly. A patch of the 19-Ma Joe Lott Tuff Member of the Mount Belknap Volcanics (Callaghan, 1939;Cunningham and Steven, 1979a;Budding and others, 1987) rests on the Osiris there; the Joe Lott is the main product of the Mount Belknap caldera, and we will visit thicker sections of this unit shortly.…”

“…The basalts have K -Ar dates of about 450,000 years (Fleck and others, 1975). Northeast of Paragonah, the 20-Ma Iron Peak laccolith marks the northeast end of the Iron Axis, and like many of these laccoliths, it breached the surface and erupted volcanic rocks Fleck and others, 1975;Rowley and others, 1994 (Callaghan, 1939;Cunningham and Steven, 1979a;Cunningham and others, 1983). The area west of this exit was mapped by Anderson (1965), some of which was published in Anderson and others (1990b).…”

“…The largest volume of bimodal rocks in the Marysvale field formed the rhyolite of the Mount Belknap Vocanics (Callaghan, 1939;Cunningham and Steven, 1979a), which was erupted between 22 and 14 million years ago from two concurrently active eruptive centers, one in the central Tushar Mountains and the other in the Sevier River valley. Thus these rhyolite eruptive centers generally coincided with areas where the older intrusive and volcanic rocks of the calcalkaline episode were deposited.…”

“…White, snow-capped peak at 2:00 is rhyolite within the 19-Ma Mount Belknap caldera (Cunningham and Steven, 1979a (Machette, 1985). On the right, a major fault scarp underlies the base of the Tushar Mountains; most of the scarp is made up of stratovolcano deposits of the Bullion Canyon Volcanics (Steven and others, 1979).…”