Late Paleozoic destruction of the western proto-Atlantic margin in the southern Appalachians

Abstract

Basement rocks (Suwannee terrane) of Florida and adjacent Georgia are composed of undeformed, unmetamorphosed lower Paleozoic shallow-water sedimentary rocks that rest upon late Precambrian-Cambrian volcanic and plutonic rocks. Paleontological and stratigraphic evidence indicates a probable affinity of this terrane with the West African rather than the North American craton. Several plate tectonic models propose that the Suwannee terrane was sutured to North America during a late Paleozoic continental collision. Delineation of this suture, based on both bore hole and geophysical data, provides no unique location. Seismic reflection profiles in southern Georgia reveal a 50-km-wide zone of SE-dipping reflectors interpreted to root at the suture zone; however, these reflectors are probably equivalent to other SE-dipping reflectors (beneath the Piedmont and adjacent Coastal Plain of south-central Georgia and South Carolina) probably associated with earlier Paleozoic structures. If basement reflectors observed in southern Georgia are products of late Paleozoic suturing, their geometry indicates a subduction zone extended beneath the Suwannee terrane before collision. Paleozoic subduction-related igneous or tectonic features are not known in the Suwannee terrane; however, extensive late Paleozoic calcalkaline plutonic activity and more restricted Barrovian-style regional metamorphism is known in the southern Appalachian Piedmont. A more consistent model for late Paleozoic collision may involve an initial phase associated with subduction beneath the Piedmont followed by collision of Africa and North America. The presence of a major embayment along the southern margin of the Appalachian-Ouachita orogen allowed juxtaposition of the Suwannee terrane next to North America by transform faulting rather than by direct collision.