Paper No. 4
Presentation Time: 8:00 AM-12:00 PM
SOUTHERN APPALACHIAN TERRANES AMENDED: TIMING OF ACCRETION AND DELIMITING PROVENANCE FROM NEW DETRITAL ZIRCON AND ND ISOTOPIC DATA
The Appalachians formed through a series of Paleozoic orogenies following the 1.1 Ga Grenville orogeny and Neoproterozoic breakup of Rodinia. The Peri-Gondwanan affinity of the Carolina terrane in the eastern Appalachians has long been accepted. Detrital zircon, Nd isotopic, and field data from west of the central Piedmont suture (CPS) characterize new and existing terranes, and require re-evaluation of provenance and terrane accretion chronology. The internal Inner Piedmont (IP) Brindle Creek fault (BCF) is a terrane boundary separating Ordovician (and older) volcanic rocks and paragneisses containing 1.4-1.0 Ga zircons in the footwall from hanging wall paragneisses with Early Devonian and older zircons (2.7, 1.8, 1.4, 1.1-0.9, and 0.6-0.45 Ga). The BCF is traceable from truncation by the CPS W of Winston-Salem, NC, through SC to truncation by the CPS in eastern GA, defining the Cat Square terrane. Detrital zircon ages, mid Paleozoic plutons (oldest is ~375 Ma), and Neoacadian (350-360 Ma) metamorphism and deformation, require that sedimentation at the Laurentian margin had ceased by ~400 Ma and that docking of the Carolina terrane likely occurred at or later than ~360 Ma. Similar stratigraphic sequences and detrital zircon suites in samples from the BCF in the IP to the eastern Blue Ridge (BR) Chattahoochee fault define the Tugaloo terrane. Two smaller terranes, Cowrock and Cartoogechaye, with contrasting sequences in higher GA-NC central BR thrust sheets contain dominantly 1.1 Ga detrital zircons with minor 1.3, 1.6, and 2.7 Ga components. The Dahlonega gold belt in a lower thrust sheet contains an Ordovician volcanic arc assemblage and paragneisses with 1.1, 1.6, 2.0, and 2.7-2.8 Ga detrital components. Inherited 1.4 and 2.6-2.9 Ga zircons have been reported for Ordovician and Devonian plutons of the western Tugaloo terrane. Nd isotopic data from Grenvillian basement and paragneisses located in western Appalachian marginal terranes yield TDM ages of ~1.5-1.6 Ga possibly connecting these terranes to the eastern granite-rhyolite province. Reported Pine Mountain window detrital zircon ages include 1.1, ~1.4 and 2.0-2.4 Ga components and are suggested to have a Gondwanan (Rondonian) source. Western terranes likely docked in the Ordovician and eastern terranes had to dock in the late Paleozoic; therefore, the Newfoundland model is not applicable to the southern and central Appalachians.