Fit of the continents around the South Atlantic (Paleoceanographic Mapping Project Progress Report No. 22-0787)
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All reconstructions proposed for the continents around the South Atlantic that require rigid plates result in substantial misfits either in the southern South Atlantic or in the equatorial Atlantic. Different solutions have been proposed to improve the fit of Africa and South America. We describe and discuss three different proposals: a model that assumes rigid African and South American plates, a model that requires an intraplate deformation zone within Africa, and a model that requires intraplate deformation within South America. Two recent plate tectonic models for opening of the South Atlantic are compared (Klitgord & Schouten 1986 and Pindell et al. in press) by calculating spreading rates and directions. Though the models that imply non-rigidity of the African and South American plates are an improvement, problems of misfit remain. In this paper we present two new reconstructions that result in an improved fit of Africa and South America. Additional constraints used in this study were derived from Seasat altimetry data. Seasat altimetry data were used to determine the directions of equatorial fracture zones which can be traced from the African to the South American margin. These fracture zones serve as tie-points for the predrift fit. Both models we propose require intraplate deformation within South America and Africa along a complex rift and strike-slip zone. Movements along these faults took place before or simultaneously with the breakup of the continents. These models eliminate gaps between the Guinea and Demarara Plateau and between the Falkland Plateau and South Africa, while avoiding large overlaps of continental margins or coastlines. Onshore geological and geophysical data, although being sparse for some regions, are consistent with the reconstructions we propose.