This project is investigating a potential connecting link in the early Paleozoic tectonics of the southern and northern Appalachians. Whereas accretion of terranes derived from Laurentia and Gondwana is recognized as the main cause of early to middle Paleozoic metamorphism and deformation to the north and south, neither exotic terranes nor major collisions with Laurentian blocks have been recognized in the Piedmont between central Virginia and the New York City area. Nevertheless, these central Appalachian rocks record pervasive and intense early to middle Paleozoic metamorphism and deformation, leading to uncertainty about both the causes of this orogenic activity and how to link early to middle Paleozoic accretion through the northern, central, and southern sectors of the Appalachians. Preliminary data from one sample from the Piedmont of central Maryland suggest that an exotic terrane may be present in this part of the central Appalachians. The main goal of this research is to take the first steps in pursuing this discovery: to confirm the presence of the exotic terrane and begin to define its spatial extent. The primary tool will be U/Pb ages from detrital zircons obtained from ten samples along strike to the north and south of the discovery sample. Because detrital zircon U/Pb ages by themselves do not unambiguously rule out a Laurentian source, research team members also will use Hf isotopic compositions in zircons, acquired in situ, to probe Laurentian versus Gondwanan sediment sources.
The new isotopic analyses acquired as part of this research may provide prima facie evidence for a spatially extensive exotic terrane in the central Appalachian Piedmont, filling much of the central Appalachian gap. This result would force a revision of our understanding of the tectonics of the central Appalachians, with implications for correlations along the entire orogen. Geologists would have a new explanation for the intense and pervasive early to middle Paleozoic deformation and metamorphism of Piedmont rocks in this region. Further, it would be possible to link in detail collision in the northern, central, and southern Appalachians, facilitating an integrated understanding of the entire orogen. This project also will support the training and education of undergraduate students; strong research and education infrastructures through collaborations with other universities; and broad dissemination of results at conferences, in papers, and through the EarthChem Library database.
