Smith River allochthon: A southern Appalachian peri-Gondwanan terrane emplaced directly on Laurentia?

The Smith River allochthon is in a southern Appalachian belt of metaclastic rocks that has traditionally been considered to be of peri-Laurentian origin. New Th-U-Pb monazite ages confirm that the allochthon was involved in an Early Cambrian tectonothermal event, indicate that it was exotic with respect to adjacent Laurentian rocks, and indicate that it is likely of Gondwanan origin. The allochthon may form a new link between the Appalachians and the Pampean terrane of western South America; in addition, its position in the orogen has implications for recent models of the opening of the Iapetus.