PROVENANCE OF BLUE RIDGE AND INNER PIEDMONT TERRANES FROM DETRITAL ZIRCON GEOCHRONOLOGY AND WHOLE-ROCK ISOTOPIC DATA, NC–SC–GA–TN

Detrital zircon geochronology from 39 samples across the Blue Ridge (BR) and Inner Piedmont (IP) of NC-SC-GA-TN combined with Sm-Nd, and Pb whole-rock isotopic data help reveal the provenances and ages of the southern Appalachian lithostratigraphic terranes. Samples were collected from the western BR (Laurentian margin), Mineral Bluff Fm. and Sevier Shale (Ordovician Taconian clastic wedge), and more easterly terranes; Cartoogechaye, Cowrock, Dahlonega, Tugaloo, Smith River, and Cat Square (CSt). U-Pb detrital zircon ages range from 2.9 Ga to 435 Ma; 1.3–0.9 Ga and less abundant 1.5-1.3 Ga zircons are common in most samples. Minor detrital zircon populations in some samples include 2.9–1.5 Ga, 754–717 Ma, 629–614 Ma, and 475–435 Ma. Similar detrital zircon populations from the western BR and terranes to the east indicate a common source for all except the CSt in the IP. The abundance of 1.3–0.9 Ga and 750–700 Ma ages is typical of BR Proterozoic crust and represents a likely source for many of the terranes. Paleoproterozoic and Archean ages require either recycling from a Mesoproterozoic metasedimentary source in the BR (e.g., Mars Hill terrane), and/or a more distal source such as the Laurentian midcontinent, or Amazonia. Limited Sm-Nd and Pb whole-rock isotopic data from detrital samples overlap data from Amazonian and BR Mesoproterozoic crust, further supporting a local provenance. The youngest detrital zircons, cross cutting relationships, and metamorphic rims on detrital zircons bracket the ages of many BR and IP lithostratigraphic units, including the Tallulah Falls-Ashe Fm. and the Coweeta Group, between 700–465 Ma. Accretion of central BR and Tugaloo terranes occurred during the Ordovician Taconic orogeny resulting in high-grade metamorphism and recycling of detrital zircons into parts of the Ordovician clastic wedge. Neoproterozoic (629–614 Ma) and Ordovician to Silurian ages occur only in samples from the CSt. The CSt contains a mixed provenance: (1) Laurentian magmatic sources (475–435 Ma) and recycled detrital zircons (1.3–0.9 Ga); and (2) peri-Gondwanan sources (629–614 Ma). It was deposited in a convergent setting between Laurentia and accreting Carolina superterrane during the Late Silurian to Early Devonian, and metamorphosed to sillimanite grade during the Late Devonian to Mississippian.