DETRITAL ZIRCON GEOCHRONOLOGY OF THE PALEOGENE MINERSVILLE CONGLOMERATE, SOUTHERN MINERAL MOUNTAINS, UTAH, USA

The Paleogene Minersville conglomerate is 10-20 m thick and occurs at the base of the east-dipping volcanic section ~3 km east of Minersville. It unconformably overlies red sandstones and shales of the Triassic Moenkopi Group and is unconformably overlain by dark-colored volcanic and volcaniclastic rocks of the Oligocene Mt. Dutton Formation. The Minersville Conglomerate is massive bedded and matrix supported. The matrix consists of red-brown medium to coarse sand rich in quartz and lithic fragments. The clasts are rounded and are mostly pebbles and cobbles of gray quartzite and brown sandstone. A total of 211 U-Pb analyses were conducted on the conglomerate sandy matrix by LA-ICPMS at the University of Arizona Laserchron Center. The detrital zircon age spectrum was diverse. About half the zircons are middle Eocene (~41-45 Ma) in age, with a maximum depositional age of 42.20±0.11 Ma and a peak age of 42.3 Ma. A mix of Mesozoic, Paleozoic, Proterozoic and Archean zircons round out the age spectrum, with peak ages of 1083 and 1427 Ma. The Eocene zircons were likely derived from the northeastern Nevada volcanic field or the recycling of the Elko Formation, which occurs in that area. The older zircons are interpreted to have been recycled from the Neoproterozoic Inkom and Caddy Canyon quartzites that occur in the hinterland of the Sevier fold and thrust belt, which also occur in the Elko area. The Minersville conglomerate was deposited prior to the inception of volcanism in the Marysvale volcanic field and prior to Basin and Range extensional faulting and may represent a proximal correlative to the Claron Formation that occurs to the east. The early development of the Ruby Mountains-East Humbolt Range core complex and the inception of the south-migrating magmatism of the ignimbrite flare up created highlands where Minersville sediment was sourced.