A solution to the Albian fit challenge between the South American and African plates based on key magmatic and sedimentary events late in the rifting phase in the Pernambuco and Paraíba basins

Abstract

Global, full-fit plate reconstruction models predict a significant presence of oceanic floor in Northeast Brazil and West Africa during Albian time, while rifting was under earlier stages in the Pernambuco and Paraíba basins. We call it the Albian breakaway gap. Sedimentary, biostratigraphic and geochronological data from the Pernambuco and Paraíba basins challenge the timing of sea floor spreading in this region. In the onshore Pernambuco Basin, there are abundant outcrops of syn-rift continental siliciclastic rocks of Aptian–Albian age interbedded with intrusive and extrusive magmatic rocks (dated ca. 102 ± 2 Ma). Salt has been recognized on seismic data within the Pernambuco Basin, but there is no record or seismic indication of salt within the Paraíba Basin. Three interpreted seismic transects provide important clues about the type of intraplate margin developed in this region. Syn and post-rift magmatism within the onshore and offshore segments of the Pernambuco Basin indicate significant melt production during (and after) the main stretching phase. On the other hand, the abruptly-necked Paraíba Basin displays seismic evidence of seaward dipping reflectors, side by side with rift sediments, suggesting the development of an Albian volcanic intraplate margin. In addition, gravity and magnetic data, on the Brazilian side, suggest a wide transition from continental to pure oceanic crust in the Pernambuco and Paraíba basins, as well as at their African counterparts: Douala, Rio Del Rey, and Lower Benue, where either oceanic crust or proto-oceanic wide crust has been recognized. Instead of pure oceanic crust, as predicted by globally balanced plate motion reconstructions, the continent-ocean transitional domain was composed in part by stretched continental crust and partially by a wide embryonic or proto-oceanic crust. In fact, a continuous and regional mid ocean ridge was only defined at the end of Albian/early Cenomanian when the South America plate was completely separated from the African plate.