Ages of the Magmatism and the Opening of the South Atlantic Ocean

The analysis of published and unpublished 368 K/Ar radiometric ages of basic, intermediate and alkaline volcanic rocks, related to the post-Paleozoic magmatism linked to the opening of the South Atlantic Ocean, yields some important evidence concerning the break up of the Gondwana supercontinent. At the Brazilian Equatorial margin, the Gondwana break up started in the Permo-Triassic, when the opening of the Equatorial South Atlantic Ocean began and spread out south-eastward up to the present day Amazon River mouth. During the middle Jurassic/lower Cretaceous (pre-Aptian), the continuity of this separation, towards the Potiguar Basin, was coeval with the northward opening of the south-east Brazilian margin, up to the Espírito Santo State latitude. The relationship between large volcanic events in the basins and the resistance to the rifting process development offered by the cratonic area was shown by the trend of the magmatic age. Along the equatorial margin, the fragmentation resistance caused by the São Luis / West African craton is manifested by a large basic magmatism described in the Tacutu, Acre, Solimões, Amazonas and Parnaíba basins. A similar mechanism along the south-east margin, is proposed for the magmatism described in the Paraná Basin which is associated with the fracturing resistance offered by the São Francisco/Congo cratonic area. The integration of geochronological, micropalentological, sedimentological and geochemical data from the basins of the east Brazilian continental margin supports a model to explain the final disruption between South America and Africa during Cenonian/Turonian time. This model implies that 90 Ma basic magmatic rocks, related to the oceanic crust formation, probably occur offshore from the present-day eastern Brazilian coast line