Print this pageConjugate Margin Studies in the South Atlantic
Blaich, Olav A.1
Faleide, Jan 
Inge
1
Tsikalas, Filippos2
Integration of regional seismic reflection/refraction and potential field data across several margin segments in the South Atlantic, complemented by crustal-scale gravity modelling, is used to reveal and illustrate the whole-crust architecture, onshore-offshore crustal structure correlations, the character of the continent-ocean boundary/transition, and the relationship of crustal structure to regional variation of potential field anomalies. Our analysis indicates the existence of a high density “transitional crust” along the northern province, where seafloor spreading does not necessarily succeed rifting straightaway. In this setting, our results favour the existence of a detachment that exhumes high-grade metamorphic lower crust from beneath the continental margin, exposing it in the deep basin at the transitional domain. Furthermore, a detailed conceptual model is developed accounting for the complex tectono-magmatic evolution of the conjugate northeastern Brazilian-Gabon margins. This model substantiates a polyphase rifting evolution mode, which is associated with a complex time-dependent thermal structure of the lithosphere. In the conjugate margin setting, asymmetric lithospheric extension resulted in the formation of the thinned continental crust domain prior to the formation of the approximately symmetric transitional domain. Along the south province of the study area, the Colorado transfer system on the Argentina margin, marks a distinct along-margin boundary in the distribution and volume of breakup-related magmatism, and appears to indicate a non-volcanic/volcanic margin boundary. In this setting, the constructed crustal transects and the available seismic reflection profiles indicate that north of the Colorado transfer system the emplacement of voluminous seaward dipping reflectors appears to be related to a high-velocity/high-density lower crustal body, suggesting that this region evolved with a rifted volcanic margin affinity and character. On the other hand, the area south of the Colorado transfer system lacks major breakup-related magmatic activity and is characterized by extremely thin crystalline crust and shallow Moho, suggesting a rifted non-volcanic margin affinity. On the conjugate South Africa margin, evidence for a magmatic lower crustal body north of Hope transfer system indicates that this region also evolved with a rifted volcanic margin affinity and character.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil