DETRITAL ZIRCONS FROM THE NEWLY DISCOVERED QUARTZITE OF ISLAND LAKE, NEOPROTEROZOIC UINTA MOUNTAIN GROUP, HIGH UINTAS WILDERNESS

Mapping in summer 2008 in the Mount Powell quadrangle defined a new quartzose stratigraphic unit below the arkosic formation of Red Castle. This new formation of Island Lake consists of > 25 m of medium to very coarse-grained quartz arenite interbedded with micaceous silty shale, siltstone and very fine quartz arenite; polymodal paleocurrents are to the south-southwest and north-northeast.

Detrital zircon populations from this formation are characteristic of quartzose marine sandstones of the Uinta Mountain Group.

Archean grains peak at 2660 Ma, and were likely derived from latest Archean zircon-rich intrusive phases of the southern Wyoming province, exposed during Neoproterozoic rifting and unroofing of the Wyoming Craton.

Paleoproterozoic grains cluster around peaks of 1650 Ma (Mazatzal), 1730 Ma (Yavapai), and 1890 Ma (Mojave).

Early Mesoproterozoic grains cluster around peaks of 1340, 1390, and 1490 Ma. This age distribution is very similar to that reported by Dickinson (2008) for anorogenic early Mesoproterozoic plutons.

Grains derived from the Grenville orogenic belt cluster around peaks of 1030, 1090, 1150, and 1210 Ma. This age distribution is similar to those reported by Eriksson et al. (2003) for modern streams draining the crystalline Appalachians and Dickinson (2008) for late Mesoproterozoic Grenville orogen and foreland satellite intrusions.

These ages reflect provenance from mixed sources mainly to the east, very similar to other quartz arenites of the Uinta Mountain Group, including the formations of Hades Pass and Mount Watson. These results support previous conclusions that the Uinta Mountain Group contains both Archean-dominated (likely fluvial-deltaic deposits derived from the Wyoming province to the north-northeast) and mixed-provenance sandstones (likely marine deposits containing sediment transported from the east via longshore currents).