Ocean basin structure offshore the Southeastern United States: Is it the rift's fault?

Continental rifts typically exhibit an asymmetrical geometry where major normal faults bound one side of a rotated block, and the rift basins thin toward the opposite hinge side. Differential extension on major faults is accommodated by transverse structures referred to as transfer zones, across which the asymmetric geometry may reverse polarity. It was proposed several decades ago that oceanic transforms between mid-ocean ridge spreading centers are inherited features of these rift-related transfer zones, and that these intra-plate structures are tectonically active. However, preserved evidence of onshore transfer zones is often lacking, particularly along the rifted margin of Eastern North America, and recent studies have suggested that oceanic transforms are not inherited structures. Observations of seismic reflection data integrated with well data show that adjacent basin bounding faults of the South Georgia Rift, a Triassic rift in the southeastern United States, occur on opposite sides of the rift flanks. The Walterboro and Warner Robins Transfer Zones identified in this study project along the small circles of Schettino and Turco (2009) into the Jacksonville and Bahamas Fracture Zones respectively. This projection is particularly interesting as it suggests the correlation of continental to oceanic features is one step south compared to previous studies which projected the Blake Spur Fracture Zone through the Charleston, SC region, and the Jacksonville Fracture Zone through Georgia. Using the same small circle solution, the Blake Spur Fracture Zone projects through the Blake Outer Ridge, a sedimentary drift which shows up prominently as a gravity anomaly the core of which has been identified as a tectonic feature reminiscent of a fracture zone on the basis of gravity modeling (Dove et al., 2007). Although no transfer zone has been identified where this small circle project onshore, it is approximately coincident with axis of the Cape Fear Arch which has been tectonically active through the Cenozoic, suggesting a link between the Blake Spur Fracture Zone and a rift transverse continental structure. The coincidence of these continental and oceanic features suggests that the structure of the oceanic crust is inherited from the initial break as originally suggested by Wilson (1965).