Abstract

New COCORP profiling in the southeastern United States has revealed a broad zone of dipping reflections that extends downward through the crust beneath the coastal plain in western Georgia. The zone is over 50 km wide, and most of the reflections dip moderately steeply toward the south. Regional considerations suggest that this feature marks the late Paleozoic suture between North America and Africa. Where crossed by the COCORP survey, the suture occurs beneath the north flank of the Triassic-Early Jurassic south Georgia basin. The main depocenter of the south Georgia basin occurs about 90 km to the south and is formed by a large half graben containing more than 5 km of rift basin fill. Farther south, the Paleozoic Suwannee basin sequence beneath northern Florida is poorly imaged on the COCORP profiles. However, weak reflections suggest that these strata (including basal felsic volcanics) may have an aggregate thickness of about 6 km in north-central Florida. At the northwest end of the COCORP traverse, a prominent horizon imaged in the upper crust beneath the inner Piedmont probably marks the southern Appalachian detachment. The detachment appears to be cut off by the Towaliga fault, implying that the Towaliga fault is in part a down-to-the-north normal fault. Intermittent Moho reflections occur at 11–12-s two-way time along the length of the COCORP survey, indicating that the crust in the region has a roughly uniform thickness of about 33–36 km (assuming an average crustal velocity of 6 km/s).

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