DETRITAL ZIRCON PROVENANCE OF CRETACEOUS TO EOCENE STRATA IN THE SEVIER HINTERLAND, CENTRAL NEVADA: IMPLICATIONS FOR TECTONICS AND PALEOGEOGRAPHY

The Late Cretaceous to Paleogene Sevier hinterland of central Nevada is generally envisioned as a high altitude, low-relief plateau following eastward propagation of the Sevier fold and thrust belt in mid Cretaceous times. New LA-ICP-MS U-Pb detrital zircon age data consisting of over 1,300 analyses from sparse Early Cretaceous to Late Eocene strata of east-central Nevada provide insight into the provenance, depositional age and paleogeography across the transition from contraction to extension. Samples collected from the syn-contractional Newark Canyon Formation type section indicate significant populations of Early Cretaceous (118-130 Ma), Silurian and dominantly Proterozoic (1.0 to 1.8 Ga) zircons, indicating a significant contribution from the coeval Cretaceous arc as well as local Paleozoic sources. A newly identified tuff from the upper lacustrine member yielded a U-Pb zircon age of 116 ± 3 Ma. In contrast, the syn-extensional Maastrichtian to Eocene Sheep Pass Formation (SPF) type section contains populations of mid-Cretaceous to Jurassic age (105 to 154 Ma) with a dominant Proterozoic population (1.0 to 1.8 Ga). The youngest zircon population within the Sheep Pass Formation significantly predates deposition by 30-40 Ma. Populations of Late Cretaceous and younger zircons are notably absent, and an upsection decrease in Mesozoic zircons may represent progressive unroofing. Additional sections of tuffaceous lacustrine strata scattered throughout east-central Nevada previously correlated to the SPF also contain abundant Proterozoic zircons, but are dominated by Late Eocene populations (38 to 35 Ma). These ages overlap with U-Pb zircon and 40Ar/39Ar sanidine tuff ages from the basal Garrett Ranch Group, which unconformably overlies the SPF type section. Together these data indicate that detrital zircon populations within the Late Cretaceous and Paleogene Sevier hinterland are dominated by recycled local Paleozoic and Mesozoic sources prior to the initiation of Late Eocene magmatism. The presence of coarse conglomerate, megabreccia and internal drainage within the SPF suggests that physical isolation from the Sierra Nevada batholith was caused by significant local relief within the Sevier hinterland following the initiation of extension in the latest Cretaceous.