Looking Outward: Constraints on the Kinematics of Oblique Devonian-Mississippian Accretion of the Peri-Gondwanan Carolina Superterrane

Middle Paleozoic terrane transfer of the peri-Gondwanan Carolina superterrane (Cs) to Laurentia is delimited by: (1) ~430 and 500-600 Ma U-Pb SHRIMP detrital zircon age populations in the Inner Piedmont (IP) Cat Square terrane (CSq); (2) 360-340 Ma U-Pb ages of zircon metamorphic rims from the IP; (3) location and southwest propagation of diachronous Acadian-Neoacadian clastic wedges; (4) transpressional orogenesis recorded by the IP; (5) the petrotectonic assemblage of the CSq; and (6) spatial and temporal relationships of Devonian to Mississippian plutonism. The IP, located along the eastern flank of the Cs from near the NC-VA border to AL, provides key constraints for Appalachian orogenesis. The IP is a broad migmatitic, sillimanite grade core that consists of the eastern part of the Laurentian Tugaloo terrane and the mixed affinity, Siluro-Devonian CSq. Metagraywacke and sillimanite schist dominate the CSq with minor amphibolite and metamorphosed ultramafic rocks. In addition to Grenvillian (1.0-1.3 Ga), detrital zircon populations from the CSq include 430, 460, 500, and 600 Ma and require a Gondwanan source during the post-Llandovery. Plutons in northern VA and MD provide possible source of ~430 Ma detrital zircons. Variations in Devonian to Mississippian magmatism include subduction-related 410-378 Ma bimodal plutons in the Cs and 407-350 Ma anatectic granites into the CSq. U-Pb ages of zircon rims from the IP range from 360-340 Ma and correspond to timing near-peak metamorphism. Excluding local areas of discordant Ar/Ar ages, a similar high-temperature event is not recognized in the Cs precluding accretion prior to the Devonian. The CSq was deposited in the Pennsylvania embayment in the remnant Rheic ocean between Laurentia and approaching Cs. Initial collision occurred near the New York promontory and migrated southward closing the basin from north-to-south and producing sillimanite grade metamorphism, partial melting, and west- to southwest-directed channel flow in the IP.