THE SUWANNEE AND UCHEE TERRANES: EXAMPLES OF INCONGRUOUS ALLEGHANIAN ACCRETION IN THE SOUTHERN APPALACHIANS

The proximity of the undeformed-unmetamorphosed Suwannee terrane (and enclosed sedimentary succession) to the purported Alleghanian suture (Suwannee suture) and the adjacent, strongly deformed, Neoproterozoic rocks of the Uchee terrane presents a significant conundrum for terrane emplacement models that call for sequential ocean closures immediately preceding assembly of Pangea. One way to gain insight into the accretionary history of the Suwannee and Uchee terranes and formation of the Gondwanan suture is to determine the cratonic provenance of both Suwannee and Uchee crust. In the Uchee terrane, U-Pb ages of zircons from metaigneous and metasedimentary rocks yield mostly Neoproterozoic ages, which suggests that Uchee crust could have formed during either the Pan-African or Trans-Brasiliano orogeny. Igneous rocks of the Suwannee terrane are of similar ages, but undeformed. In the Suwannee terrane, ~2 km of lower Paleozoic clastic sedimentary rocks have been correlated specifically with similar rocks in the Bove basin (West Africa). The U-Pb age spectra of detrital zircons from the Suwannee succession show a clearly non-Laurentian signature with well-defined concentrations of ages corresponding to the Pan-African/Trans-Brasiliano and the Birimian/Trans-Amazonian orogenic events, i.e., the same as found within the Uchee terrane. Significantly, Grenville-age zircons, which dominate lower Paleozoic sediments in Laurentia north of the Suwannee suture, are notably lacking in the Suwannee and Uchee samples. U-Pb ages of detrital zircons from a range of Paleozoic sedimentary rocks within the Bove basin indicate a more diverse provenance. Some Bove samples have strong concentrations of Pan-African and Birimian/Trans-Amazonian ages, similar to Suwannee terrane samples. Other samples, however, have strong concentrations of ages in the range 1200–1300 Ma and lesser concentrations of older zircons (e.g., Birimian/Trans-Amazonian). Overall, the detrital-zircon age-spectra from strata in the Bove basin do not suggest a unique or comprehensive match in provenance to the Suwannee samples. Although not definitive, these data are permissive of a pre-Pangean Suwannee–Bove connection, but require that changes in provenance of the Bove samples were only partially captured in the Suwannee succession.