A Época de Abertura do Oceano Atlântico Sul com Base em Dados Paleomagnéticos

Abstract

African palaeomagnetic poles for the Triassic, Jurassic and Cretaceous were compared with the corresponding poles of South America in the pre-drift reconstruction of the continents after Martin et al. (1981), by means of an F-test. The test showed that the pre-drift reconstruction is consistent with the palaeomagnetic data for the Triassic, but there is a significant difference between the corresponding Jurassic, Lower Cretaceous and Upper Cretaceous palaeopoles for the two continents, with an error probability of less than 5%. Comparing the pole positions for South America and Africa in a configuration that indicates a small separation between the two continents, as the one suggested by Sclater et al. (1977) for 110 m.y. B.P., one finds a significant difference for the Triassic palaeopoles. The Jurassic and Lower Cretaceous poles are consistent with that separation of the continents. The reconstruction for 80 m.y. B.P. after Francheteau (1973). for a larger separation between the continents, is consistent with the Upper Cretaceous palaeomagnetic poles. Assuming the movements of crustal blocks relative to each other as rigid blocks, the results of the F-test indicated that South America and Africa were close together during the Triassic. There was a small separation between the continents in the Jurassic and this separation was stationary until Lower Cretaceous time. The upper Cretaceous data are compatible with a fast and significant spreading of the continents in that period.