U-Pb zircon dates from the central Appalachian Piedmont: A possible case of inherited radiogenic lead

摘要

Zircon dates from metavolcanic and metaplutonic rocks of the central Appalachian Piedmont in Maryland and Virginia are important for interpreting the age of the Glenarm Series. Compilation and evaluation of available data from this area suggest that Piedmont zircons may have inherited a component of older radiogenic lead in seed crystals, which were derived from the Pre-cambrian basement complex. The zircons were also affected by lead and uranium loss during subsequent Paleozoic metamorphism recorded in the Piedmont terrain and (or) recent dilation of the rock at surface conditions. Thus, the apparent dates might not represent precise rock ages, but may still give valuable information about the evolution and history of the rocks.