Kinematics of the South Atlantic rift

Abstract

The South Atlantic rift basin evolved as branch of a large Jurassic-Cretaceous intraplate rift zone between the African and South American plates during the final breakup of western Gondwana. While the relative motions between South America and Africa for post-breakup times are well resolved, many issues pertaining to the fit reconstruction and particular the relation between kinematics and lithosphere dynamics during pre-breakup remain unclear in currently published plate models. We have compiled and assimilated data from these intraplated rifts and constructed a revised plate kinematic model for the pre-breakup evolution of the South Atlantic. Based on structural restoration of the conjugate South Atlantic margins and intracontinental rift basins in Africa and South America, we achieve a tight fit reconstruction which eliminates the need for previously inferred large intracontinental shear zones, in particular in Patagonian South America. By quantitatively accounting for crustal deformation in the Central and West African rift zone, we have been able to indirectly construct the kinematic history of the pre-breakup evolution of the conjugate West African-Brazilian margins. Our model suggests a causal link between changes in extension direction and velocity during continental extension and the generation of marginal structures such as the enigmatic Pre-salt sag basin and the São Paulo High. We model an initial E–W directed extension between South America and Africa (fixed in present-day position) at very low extensional velocities until Upper Hauterivian times (≈126 Ma) when rift activity along in the equatorial Atlantic domain started to increase significantly. During this initial ≈17 Myr-long stretching episode the Pre-salt basin width on the conjugate Brazilian and West African margins is generated. An intermediate stage between 126.57 Ma and Base Aptian is characterised by strain localisation, rapid lithospheric weakening in the equatorial Atlantic domain, resulting in both progressively increasing extensional velocities as well as a significant rotation of the extension direction to NE–SW. From Base Aptian onwards diachronous lithospheric breakup occurred along the central South Atlantic rift, first in the Sergipe-Alagoas/Rio Muni margin segment in the northernmost South Atlantic. Final breakup between South America and Africa occurred in the conjugate Santos–Benguela margin segment at around 113 Ma and in the Equatorial Atlantic domain between the Ghanaian Ridge and the Piauí-Ceará margin at 103 Ma. We conclude that such a multi-velocity, multi-directional rift history exerts primary control on the evolution of this conjugate passive margins systems and can explain the first order tectonic structures along the South Atlantic and possibly other passive margins

Kinematic Evolution of the Southern North Atlantic: Implications for the Formation of Hyperextended Rift Systems

“…Boundaries between each domain are of particular importance for plate kinematic, but one question that needs to be addressed is whether a domain boundary can be considered to be a spatiotemporal marker. In this study, we defined and mapped the necking line (NL), the oceanward edge of the continental crust (ECC), and the continentward limit of first oceanic crust, referred to as the Landward Limit of Oceanic Crust (LaLOC) (Heine et al, ).…”

“…The remaining cross section is formed by the thinned continental crust of the two conjugate margins. The extension of this deformed continental crust has to be taken into account for palinspastic restorations (e.g., Aslanian & Moulin, ; Dunbar & Sawyer, ; Heine et al, ; Williams et al, ). As magma‐poor margins do not have a large amount of magmatic additions, we assume that the surface of thinned continental crust is equal to the initial crustal surface (no gain or loss of continental crust).…”

“…Nevertheless, their integration in kinematic plate models remains complex. Previous studies proposed palinspastic restorations (e.g., Heine et al, ; Hosseinpour et al, ; Williams et al, ). However, they only use two rotation poles, one at full fit and the second at the first magnetic anomaly, assuming therefore a continuous evolution during rifting.…”

Style of rifting and the stages of Pangea breakup

“…It is as if this major heritage was used to channel the northward propagation of the rift system toward the Tethys realm ( Figure 5). Interestingly, the two major rift systems [Jackson et al, 2000;Szatmari, 2000;Moulin et al, 2010;Heine et al, 2013;Franke, 2013], central Indian [Gaina et al, 2007], and the Bay of Biscay together with the southern part of the North Atlantic located between the Iberia-Newfoundland conjugate margins Boillot, 1984;Tucholke et al, 2007;Péron-Pinvidic et al, 2007;Tugend et al, 2014].…”

Getting over continent ocean boundaries

“…In its simplest form, this may involve determining the cross sectional area of extended continental crust imaged by a seismic profile and balancing this with the area in a shorter profile with crust of some assumed pre-extensional thickness (e.g. Heine et al, 2013). Working similarly, but in three dimensions, a set of plate rotation parameters can be assumed as known in order to define profiles along which to exactly balance the crustal thickness sampled from a grid (e.g.…”