Gondwanan and Peri-Gondwanan Crustal Elements Transferred to the Southeastern U.S. during Grenvillian and Paleozoic Orogenies: Evidence from Digital Aeromagnetic and Gravity, Geologic, and Geochronologic Data

Peri-Gondwanan (PG) crust has long been recognized from fossils and geochronologic data in the southern Appalachian Carolina superterrane, where Neoproterozoic (630–550 Ma) arc volcanism was followed by deposition of Neoproterozoic to Middle Cambrian clastic/volcaniclastic sedimentary rocks and ~535 Ma regional metamorphism. Gondwanan (African) basement and Paleozoic cover are known from drill holes in the Suwannee terrane (FL). Pb isotopic data indicate that all exposed Southern Appalachian Grenvillian rocks are Gondwanan, with the Laurentia-Gondwana suture west of the Blue Ridge–Piedmont allochthon (possibly the NY–AL magnetic lineament).

Digital aeromagnetic and gravity data provide critical information on location, crustal character, and geometry of boundaries between crustal blocks of contrasting potential-field signatures. Exposed Carolina superterrane rocks have potential-field signatures contrasting with Laurentian terranes to their west. PG crustal blocks are traceable beneath the Atlantic and Gulf Coastal Plain based on their 3-20 km, high frequency signature interrupted by numerous plutons. The Brunswick (Charleston) terrane has a slightly different signature, but a 604 Ma U-Pb TIMS date from one drill hole in GA suggests that it also is PG crust. Suwannee terrane rocks south of the Suwannee-Wiggins suture also have a distinctive magnetic-gravity signature of 20-50 km, broad, elliptical highs and lows. This suture joins Laurentia to Gondwanan and PG crust, but truncates all Southern Appalachian Grenvillian and PG terranes, indicating that it formed during the final (Alleghanian–Variscan) collision that also formed Pangaea, and that it was left behind during Mesozoic rifting. This Paleozoic suture may coincide with a failed Mesozoic rift, because drill hole and potential-field data indicate a considerable thickness of Mesozoic sediments above the suture.