RETHINKING LATE STAGE ALLEGHANIAN TECTONICS: THE IMPORTANCE OF THE CAROLINA-MISSISSIPPI FAULT IN PANGEA RECONSTRUCTION MODELS FOR THE EARLY PERMIAN

The nature of Late Paleozoic tectonics in the southeastern United States remains a critical aspect of Pangean tectonics, due to the proximal location associated with the terminal collision of Laurentia and Gondwanna. Early recognition of Paleozoic strata in the southeastern U.S.A., foreign to North America, led to acknowledgment that Pangean rifting and associated opening of the Atlantic Ocean left Gondwanan terranes sutured to North America. Considerable effort has since been placed on determining a reliable tectonostratigraphic model and a corresponding tectonic history between the Laurentian, Peri-Gondwanan, and Gondwanan terranes. In the Southern Appalachians, models vary widely in regards to the final stages of the Alleghanian orogeny; from a zone of mainly dextral, transpressional shearing to a near head-on collision with Gondwana overthrusting Laurentia. An accurate model on the local scale is pivotal, as these provide strong geological constraints for the many Pangean and proto-Pangean reconstruction models (notably A, A1, A2, B, and C) suggested for the Late Paleozoic. With mutually-exclusive models presented that may all be reasonable from a paleomagnetic standpoint, the selection as to which Pangea model is most plausible must integrate local geology.

The majority of Pangea models suggest significant amounts of dextral movement between Laurentia and Gondwana leading up to the formation of Pangea, but estimates of timing vary from 330 Ma to 260 Ma with Pangea B proposing that dextral movement occurred after the main orogenic events were over. New geologic and geophysical evidence from the Suwannee Basin strata supports the presence of a narrow transcurrent shear zone, originally termed the Carolina-Mississippi fault, separating not only Laurentian and Gondwanan affinity terranes but also truncating all known Alleghanian structures. The tectonostratigraphic relations along this feature, therefore, have wide-reaching implications on Pangea models. The Carolina-Mississippi fault, proposed to be renamed the Pangean Transcurrent Fault Zone, provides strong evidence that dextral shearing may have not only occurred pre- and syn-Alleghanian but must have continued after major thrusting had ended in the Southern Appalachians. This would be in agreement with a model more similar to Pangea B.