PROVENANCE OF THE EOCENE CLARON FORMATION OF THE SEVIER PLATEAU, UTAH, USA

Three catastrophic landslides that make up the late-Oligocene-to-Miocene Marysvale Gravity Slide Complex (MGSC) in Southwest Utah are hypothesized to have been driven by regional inflation of the Marysvale Volcanic Field (MVF). Here we assess the provenance of pre-volcanic strata that form the floor and the environs of the MVF to constrain the regional paleogeography prior to volcanism. Detrital zircon U-Pb analyses (LA-ICPMS) were conducted on the matrix of conglomerate beds of the Eocene Claron Formation (s=4, z=559) and the overlying Oligocene Boat Mesa conglomerate (s=1; z=178) and show a shift in provenance over time. The detrital zircon age spectra of the red member (lower) of the Claron Formation in Casto Canyon is dominated by Mesoproterozoic zircons that we interpret were recycled from Neoproterozoic Proterozoic-Mesozoic strata exposed in the Sevier thrust belt, which was proximal and to the west of the Claron Basin. The overlying white member of the Claron Formation also is dominated by Mesoproterozoic zircons but has a higher proportion of Grenville-age grains (1250-1000 Ma). All Claron samples are statistically indistinguishable. The Boat Mesa Conglomerate is dominated by Jurassic grains that were sourced from the Cordilleran arc in the Sevier hinterland, indicating the loss of prominence of the Sevier Fold and thrust belt at this latitude by Eocene time. The Boat Mesa Conglomerate is overlain by the volcanogenic Brian Head Formation, which was sourced by the Indian Peak Caldera complex, several hundred kilometers to the west. Thus, these data indicate that the Laramide compression in this region had abated by the end of Claron deposition which is revealed by a shift in sediment provenance from proximal sources in the Sevier foreland to distal sources in the Sevier Hinterland.