HAFNIUM ISOTOPES OF GRENVILLE DETRITAL-ZIRCONS IN THE APPALACHIAN FORELAND BASIN: IMPROVING PROVENANCE RECONSTRUCTIONS

The Grenville Orogeny was the one of the largest crustal building events in the Earth’s history. Due to the large volume and zircon fertility of the material generated, Grenville zircons are present across North America. Grenville source rocks typically have similar crystallization ages, thus the standard technique of using uranium-lead ages (U-Pb) to determine provenance is of little use beyond inferring a general source area in eastern North America. This combination of Grenville detrital zircons in the stratigraphic record coupled with a very limited ability to pinpoint provenance is central to what we term the “Grenville Problem.” Recent data suggest the hafnium isotopic composition (εHf) of zircons in Grenville-age rocks vary from south to north along the eastern United States. Theoretically, the εHf of detrital zircons shed from these rocks should also vary from south to north. The Appalachian foreland basin contains abundant detrital zircons of Grenville age that were eroded from Grenville source rocks and Precambrian passive margin sediments as they were exposed during the Taconic, Acadian, and Alleghanian orogenies. Thus, the question is whether the εHf values of Grenville detrital zircons in the Appalachian foreland basin reflect the trends seen in the Grenville source rocks. This study will examine the εHf values of Grenville detrital zircons from strata deposited in the Appalachian foreland basin. The hypothesis to be tested is that the εHf variations in detrital zircons vary from south to north, consistent with the variations observed in the Grenville rocks. Samples from across the Appalachian foreland basin were collected and analyzed for U-Pb ages and εHf values. The results of this study will shed light on how well foreland basin sediments record εHf variations in source rocks. The implications of the study are for understanding basin-scale sediment transport patterns in foreland basins and for reconstructing trans-continental sediment dispersal.