U-PB AGES OF DETRITIAL ZIRCONS FROM SANDSTONE IN THE LATE DEVONIAN GUILMETTE FORMATION OF SOUTHEASTERN NEVADA

SHRIMP U-Pb geochronology analysis was conducted on 40 zircon grains from a Late Devonian sandstone of the Upper Member of the Guilmette Formation, 45 m above the Alamo Breccia Member at its stratotype locality in the Pahranagat Range, Nevada. The sandstone interval of the Upper Member is a mature, medium to fine grained quartz arenite that extends into Utah with thicknesses ranging up to 300 m. The sample was taken from the base of the sandstone interval, where it is mostly massive and occasionally planar laminated with a dominant paleocurrent from the northeast. Due to its maturity, the sandstone of the Upper Member is conventionally thought to be the product of recycling from earlier mature sandstone deposits, primarily the Ordovician Eureka Quartzite, and possibly derived from uplifted terranes associated with the Antler Orogeny. Determining the source area of the Guilmette sandstone therefore constrains the influence of Antler uplift versus eustatic controls on siliciclastic deposition.

Detrital zircons cluster in age populations of 1.63–1.73 Ga and 1.39–1.47 Ga with minor populations of 1.03–1.18 Ga, ~1.8 Ga, and ~2.7 Ga. The dominant grain populations suggest input from the Paleoproterozoic Yavapai and Mazatzal provinces and Mesoproterozoic A-type granites, both sourced from the southwestern US, and minor zircon populations of Grenville and Archean ages from exposed basement rocks or platformal sediments. The pattern of zircon ages of the Guilmette sandstone is inconsistent with zircons dated from the Eureka Quartzite, which contains distinct populations of 1.8–2.4 Ga grains derived from the Peace River Arch region. Instead, the Guilmette sample is most similar to sandstones of the Middle Devonian Oxyoke Canyon Sandstone Member of the Nevada Formation, sampled from the Diamond Range near Eureka, Nevada (Gehrels and Dickinson, 1995). Our results suggest that the Guilmette sandstones either were formed by reworking of the Oxyoke sandstones or, more likely, derived from primary sediments shed from similar cratonal rocks as the Oxyoke sandstones. The zircon ages of the Upper Member sandstone suggest that eustatic sea level drawdown, rather than deep incision into Ordovician quartzites by Antler uplift, may account for siliciclastic deposition on the carbonate shelf during the Late Devonian.