HAFNIUM ISOTOPE SYSTEMATICS OF GRENVILLE DETRITAL ZIRCONS IN THE APPALACHIAN FORELAND BASIN

Sandstones across North America contain detrital zircons derived from rocks associated with the Grenville Orogeny (ca. 900-1350 Ma). Recent data indicate U-Pb ages and eHf values of zircons in Grenville source rocks in the eastern United States vary from north to south (e.g., Mueller 2013), suggesting the possibility of more specific detrital zircon provenance reconstructions. We sampled Pennsylvanian-age sandstone units in the Appalachian foreland basin over a 1000 km north-south transect in order to examine potential trends in detrital zircon U-Pb ages and eHf values in the sedimentary record. Samples were collected from the Pottsville Formation in Pennsylvania, the Pocahontas Formation in West Virginia, the Lee Formation in Virginia, the Sewanee Formation in Tennessee, and the Montevallo Formation in Alabama. The Grenville detrital zircons from these samples have eHf values between -3 and +10 (n=90), with an average value of 4.1. U-Pb ages and eHf values tend to covary, with more positive eHf values associated with older Grenville detrital zircons and more negative eHf values associated with younger Grenville detrital zircons. This relationship between U-Pb age and eHf values in the detrital record supports recent hypotheses correlating zircon age and eHf values in Grenville source rocks (Mueller et al. 2016). Spatial trends in U-Pb age and eHf values of Grenville detrital zircons are not observed in Pennsylvanian-age strata of the Appalachian foreland basin. All samples along the north-south transect contain Grenville detrital zircons with similar or overlapping eHf values and U-Pb ages. The similar values in Grenville detrital zircon U-Pb ages and eHf at each sampling location can be explained by several hypotheses, each of which requires additional data and further testing. We hypothesize that many of the Grenville detrital zircons in the Pennsylvanian-age foreland basin strata were recycled from previously homogenized sources of Grenville detrital zircons, including upper Proterozoic-lower Paleozoic sedimentary rocks.