Insights into the mode of the South Georgia rift extension in eastern Georgia, USA

- Triassic extension was characterized in eastern Georgia to identify rift mode.
- Analog and numerical models are applied to geology and geophysical relations.
- A tectonic progression is developed to explain core complex mode extension.
- Core complex mode extension constrained lithospheric conditions as young and warm.
- The South Georgia rift is proposed to be part of buried Eagle Mills series of rifts.

The South Georgia rift (SGR) lies oblique to the east coast margin of North America and across the Alleghenian suture between Laurentia and Africa in southern Georgia. Regionally, the SGR can be divided into a southwest compartment and a northeast compartment across the Jacksonville structure that is located in the vicinity of that suture. Analytical and numerical models are used to characterize the mode of rifting in the northeast compartment. Borehole, COCORP seismic, and regional geophysical information from the compartment, that were used previously to infer the geometry of the basin, are reassessed with the use of those models to analyze the lithospheric conditions influencing Triassic extension. This approach led to the interpretation of core complex mode extension and to the proposal of a model of progressive rifting. The model shows how the Riddleville and Main SGR basins are associated and how changes in structural style of those two basins resulted from changing lithospheric conditions during extension. The core complex model also indicated that extension was influenced by distributed deformation of a younger, warmer, and less stable lithosphere adjacent to the Permian suture; whereas extension in other east coast rifts that lie subparallel to structural fabric was probably localized by preexisting zones of weakness.