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The three southernmost external Appalachian Grenville basement massifs occur in the Georgia western Blue Ridge, where they core map-scale, inclined-to-recumbent, west-vergent isoclinal anticlinoria formed during peak greenschist-facies Paleozoic metamorphism. The massifs are in thrust contact with Cambrian rocks of the adjacent foreland thrust belt. The basal cover unit of each massif, the Pinelog Formation, is likely correlative with the Late Proterozoic Snowbird Group of the Ocoee Supergroup. This sequence was deposited in fluvial-alluvial to shallow-water deltaic to intertidal environments adjacent to sharp basement uplifts, most probably along extensional fault scarps during initial Late Proterozoic rifting of Laurentia. A second phase of more extensive continental rifting and subsidence followed with deposition of the Great Smoky Group, a mostly deep-water turbiditic sequence. During the second rift cycle, a large (>2000 km2) block, which included much of the Georgia western Blue Ridge and contained the deposits of the earlier rift basin, was tilted westward with the underlying basement along a southeast-dipping extensional fault system (stratigraphic offset >1 km) flanking the western margin of the Blue Ridge. Great Smoky units lie unconformably above this block and progressively cut deeper into the underlying cover sequence and then into the basement toward the east. This northwest-border fault system was bounded to the southwest by a large continental transfer (transform) fault, which marked the southern limit of the Ocoee basin, and across which the polarity of faulting along the rifted margin was reversed. Internal thrusts associated with Alleghanian continental collision, e.g., the frontal Blue Ridge thrust, were likely rooted below the basement massifs because the massifs had been previously detached from autochthonous basement by the two earlier cycles of rift-related faulting.

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