Provenance of the lower ocoee supergroup, eastern great smoky mountains

Provenance and tectonic setting of clastic rocks of the Neoproterozoic Ocoee Super- group were assessed using modes of detrital framework minerals, detrital feldspar chem- istry, whole-rock geochemistry, heavy min- eral assemblages and chemistry, and detrital zircon U-Pb geochronology. Putative source rocks comprising locally exposed Gren- ville basement were analyzed for compari- son. Samples studied are primarily arkosic to subarkosic siltstones, sandstones, and minor conglomerate. Ternary tectonic dis- crimination diagrams indicate a continental basement uplift setting, although the min- eralogically most mature Longarm quartz- ite indicates a continental interior setting. The range of detrital feldspar compositions among Ocoee units is comparable to feldspar in basement rocks. Orthoclase-rich detrital alkali feldspar predominates over detrital al- bitic plagioclase. Whole-rock normative Qz- Or-Pl values and trace-element abundances closely match those of local basement. Snow- bird Group siltstones and sandstones contain high abundances of zircon, apatite, titanite, ilmenite, and epidote, which locally occur as concentrations of heavy minerals in discrete laminae. Zircon-tourmaline-rutile indices and titanite compositions are most consis- tent with a granitic source for these sedi- ments. The majority of detrital zircon U-Pb ages are late Mesoproterozoic, with scattered late Neoproterozoic and Paleoproterozoic grains. All but one of the ~1200 detrital zir- cons (at ca. 2000 Ma) can be accounted for by a local Blue Ridge basement magmatic source terrane. Archean detrital zircon ages are absent from the Ocoee detrital zircon age population. This absence is consistent with the general paucity of Archean grains in other Neoproterozoic Southern Appalachian clastic sequences. All data are consistent with a lithologically and geochronologically restricted, proximal, flank source for sedi- ment filling a marginal continental rift. The Ocoee represents the first pulse of sediment dominated by Grenville-age zircon on the eastern Laurentian margin and serves as a major source of recycled zircon for Paleozoic clastic sequences in eastern Laurentia. The youngest detrital zircon age obtained from the basal Ocoee Wading Branch Formation (639 ± 8 Ma) provides a maximum depo-sitional age for the Ocoee Supergroup and onset of rift-filling sedimentation in the intra-continental Ocoee basin.