Is the Brunswick magnetic anomaly really the Alleghanian suture?

Abstract

The southeastern margin of the United States presents a complex picture of accreted Paleozoic terranes and a rift‐related Mesozoic overlap assemblage buried by a thick veneer of Coastal Plain sediments. Basement terranes have been defined on the basis of drilling and geophysical data. Their relationship to each other and to plate tectonics is in debate. The Brunswick magnetic anomaly in Georgia has been cited as the location of the late Paleozoic suture between North America and a continental fragment with African affinities known from the northern Florida subcrop. This paper poses a new plate model for this region based upon the following assumptions: (1) that deep well tests furnish a reasonable data set for the discrimination of various basement rock types across the region and (2) that the Brunswick anomaly is the outboard limit of the North American Piedmont/Avalon terrane. We propose that the area between the northwest limit of “African” rocks and the trace of the Brunswick anomaly is a region of crustal overlap, as African‐related rocks were overthrust to the northwest. The original irregular outline of the North American continental margin and the landward extensions of oceanic fracture zones are intimately related to the kinematics of suspect terranes in the Appalachian orogen. The implications of the model suggest that differential shortening during collision and differential extension during subsequent rifting accommodate movements on repeatedly activated transforms.