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Recently acquired COCORP profiles in the southeastern United States show that: 1) Reflections associated with the Appalachian detachment are prominent beneath the Inner Piedmont of western Georgia, but do not extend further southeast beneath the Pine Mountain belt. 2) The Brunswick magnetic low is associated with a broad zone of crustal-penetrating dipping reflections that probably marks the Alleghanian suture in the southeastern U.S. 3) The South Georgia basin is a composite feature consisting of several half-graben, locally containing >5 km of Triassic -E. Jurassic basin fill. These basins occur within the interior of the Alleghanian orogen, but are not specifically associated with Alleghanian suture. 4) Across-strike crustal thickness variation, and distribution and character of lower-crust and Moho reflections in the Southern Appalachians is grossly similar to that observed in other parts of the AppalachiadHercynian orogenic belt. Global comparisons suggest that these regional variations are a consequence of post-collisional extensional tectonics, rather than a primary (Palaeozoic or older) feature of the orogenic belt.

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