Assembling the Blue Ridge and Inner Piedmont: Insights Into the Nature and Timing of Terrane Accretion in the Southern Appalachian Orogen from Geologic Mapping, Stratigraphy, Kinematic Analysis, Petrology, Geochemistry, and Modern Geochronology

Detailed geologic mapping, SHRIMP U-Pb zircon geochronology, geochemistry, petrology, and structural and kinematic analyses were applied to decipher the structure, tectonic heredity, and Paleozoic accretionary history of suspect terranes of the southern Appalachian Blue Ridge (BR) and Inner Piedmont (IP). Detailed geologic mapping in the Waynesville and Sam Knob 7.5-minute quadrangles recognized the Great Balsam Mountains window cored by sillimanite I and II zone Dahlonega gold belt rocks, overthrust by migmatitic biotite gneiss of the Cartoogechaye terrane to the northwest, and migmatitic Tallulah Falls Formation of the Tugaloo terrane to the southeast. Suspect terranes of the BR and IP consist of peri-Laurentian and mixed Laurentian and peri- Gondwanan heredities and were accreted to the Laurentian margin during the Taconian, 465–450 Ma, and Neoacadian, 365–340 Ma, orogenies. Detrital zircon populations of 1.3–0.9 Ga, 1.5–1.3 Ga, and 750–700 Ma from the Cartoogechaye, Cowrock, Dahlonega gold belt, and Tugaloo terranes indicate a dominantly Laurentian provenance. Minor Paleoproterozoic populations in these terranes suggest input from distal terranes of the Laurentian mid-continent or the Amazonian craton. Detrital Paleozoic zircons, 460–430 Ma, occur only in samples from the Cat Square terrane and Smith River allochthon. Ordovician and 600–500 Ma detrital zircons from the Cat Square terrane document the first occurrence of peri-Gondwanan material deposited in a convergent setting between Laurentia and the approaching Carolina superterrane during the Late Silurian to Early Devonian. Palinspastic reconstruction of the Cat Square basin suggests a paleogeographic location in the Pennsylvania embayment and links deformation in the crystalline core with progradation of the Devonian clastic wedge. Metamorphic zircons from central BR terranes yield U-Pb ages of 465–450 Ma, and delimit accretion to the Laurentian margin and metamorphism to amphibolite and granulite facies during the Taconian orogeny. U-Pb ages of metamorphic zircons from the IP yield ages of 392–344 Ma corresponding to upper amphibolite facies metamorphism associated with the Devonian–Mississippian collision of the Carolina superterrane during the Neoacadian orogeny. The IP and parts of the eastern BR flowed west and southwest out from beneath the overthrust Carolina superterrane as an orogenic channel.