Structure and evolution of adjoining segments of the West African margin determined from deep seismic profiling

Wannesson, J.; Icart, Jean-Claude; Ravat, J.

doi:10.1029/gd022p0275

Cited by 18 publications

(25 citation statements)

References 4 publications

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“…In particular, along the northeastern Brazil-Gabon conjugate margin, the data set was provided courtesy to Statoil and comprises seismic reflection profiles acquired by TGS-NOPEC (Camamu/Almada basins) and ION-GXT (South Gabon Basin). Published seismic reflection [Rosendahl et al, 1991;Meyers et al, 1996aMeyers et al, , 1996bRosendahl and Groschel-Becker, 1999;Rosendahl et al, 2005] and wideangle refraction profiles [Wannesson et al, 1991] along the Gabon margin have also been analyzed, revised and incorporated into our interpretations. Farther south, along the conjugate southeastern Brazil-Angola margin, industrial reflection seismic profiles acquired by Fugro Multi Client Services (Espírito Santo Basin) were at our disposal.…”

Section: Discussionmentioning

confidence: 99%

“…Since an anomalous high-velocity/density lower crust has been described along the northern Angola (Lower Congo Basin) [Contrucci et al, 2004] and southern Gabon margins [Wannesson et al, 1991;Blaich et al, 2010], the possibility exists that such lower crust is also present along the Kwanza Basin. However, with the available data and due to the nonunique interpretation of gravity anomalies, it is impossible to resolve this issue.…”

Section: Crustal Architecturementioning

confidence: 99%

“…Even though the Moho discontinuity is poorly constrained by seismic imaging along the Gabon margin, gravity modeling indicates a continental crust that thins gently toward the west, indicating a gentle crustal taper ( Figure 3a). The high-amplitude and subhorizontal band of seismic reflections located at a depth of ∼16-18 km (Figure 3a) exhibits the upper boundary of a velocity increase from 6.1 to 6.9 km/s [Wannesson et al, 1991]. Furthermore in order to accomplish a reliable fit in the gravity modeling a high-density (3100 kg/m 3 ) is required for the lower crust [Blaich et al, 2010].…”

Section: Crustal Architecturementioning

confidence: 99%

“…In addition, the transitional domain along the Espírito SantoKwanza conjugate basins is considerably wider than the transitional domain along the Camamu-Gabon conjugate basins (Figure 7). North of the Salvador-N'Komi transfer zones, it seems to be an overlap of the COB, meaning that the prominent conjugate Salvador-N'Komi transfer zones appear to be first-order structural elements, governing the margin segmentation and evolution and may have acted as an intraplate decoupling zone [Teisserence and Villemin, 1989;Wannesson et al, 1991;Blaich et al, 2010].…”

Section: Continent-ocean Transitional Domainmentioning

confidence: 99%

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Crustal breakup and continent-ocean transition at South Atlantic conjugate margins

Blaich¹,

Faleide²,

Tsikalas³

2011

J. Geophys. Res.

150

174

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[1] Seismic reflection and refraction profiles, and potential field data, complemented by crustal-scale gravity modeling and plate reconstructions are used to study the evolution of the central and south segments of the South Atlantic conjugate margins. The central segment is characterized by a hyperextended continent-ocean transitional domain that shows evidence of rotated fault blocks and a detachment surface active during rifting. A polyphase rifting evolution mode, associated with a complex time-dependent thermal structure of the lithosphere, is substantiated for the central segment that is not a "magma-poor" end-member. Increase of volcanic activity during the late stages of rifting may have "interrupted" the extensional system implying a failed exhumation phase that was replaced instead by continental breakup and emplacement of fully igneous crust. The continent-ocean transitional domain along the "magma-dominated" south segment is characterized by a large volume of flood basalts and high-velocity/high-density lower crust. The northern province of the south segment is characterized by symmetrical seaward-dipping reflections and symmetrical continent-ocean transitional domain. The influence of the Tristan da Cunha plume on this province is very likely. The central province of the south segment is characterized by along-strike tectonomagmatic asymmetry, which can be caused by the initial continental stretching and accompanying magmatism rather than by the subsequent seafloor spreading. The Tristan da Cunha plume on the central province may have influenced the volume of magmatism but did not necessarily alter the process of rifted margin formation, implying that the central province of the south segment may have much in common with "magma-poor" margins.

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Section: Discussionmentioning

confidence: 99%

Section: Crustal Architecturementioning

confidence: 99%

Section: Crustal Architecturementioning

confidence: 99%

Section: Continent-ocean Transitional Domainmentioning

confidence: 99%

See 2 more Smart Citations

Crustal breakup and continent-ocean transition at South Atlantic conjugate margins

Blaich¹,

Faleide²,

Tsikalas³

2011

J. Geophys. Res.

150

174

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“…The margin structure north of the Walvis Ridge has been investigated by several deep-seismic experiments since the early 90's and an increasing amount of data is being released and reprocessed Wannesson et al, 1991;Meyers and Rosendahl, 1991;Moulin et al, 2001;Dupré, 2003;Contrucci et al, 2004). The continental margin across the Angola segment comprises a 150 km-wide zone of extremely thinned continental crust (5 to 8 km thick), which is overlain by a 10-12 km sedimentary prism, and underlain by an anomalously high velocity zone, at the transition with moderately extended continental crust.…”

Section: Crustal Structurementioning

confidence: 99%

South Atlantic continental margins of Africa: A comparison of the tectonic vs climate interplay on the evolution of equatorial west Africa and SW Africa margins

Séranne¹,

Anka²

2005

Journal of African Earth Sciences

132

106

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Africa displays a variety of continental margin structures, tectonic styles and sedimentary records. The comparative review of two representative segments: the equatorial western Africa and the SW Africa margins, helps in analysing the main controlling factors on the development of these margins. Early Cretaceous active rifting south of the Walvis Ridge resulted in the formation of the SW Africa volcanic margin that displays thick and wide intermediate igneous crust, adjacent to a thick unstretched continental crust. The non-volcanic mode of rifting north of the Walvis ridge, led to the formation of the equatorial western Africa margin, characterised by a wide zone of crustal stretching and thinning, and thick, extensive, synrift basins. Contrasting lithologies of the early post-rift (salt vs shale) determined the style of gravitational deformation, whilst periods of activity of the decollements were controlled by sedimentation rates. Regressive erosion across the prominent shoulder uplift of SW Africa accounts for high clastic sedimentation rate during Late Cretaceous to Eocene, while dominant carbonate production on equatorial western Africa shelf suggests very little erosion of a low hinterland. The early Oligocene long-term climate change had contrasted response in both margins. Emplacement of the voluminous terrigenous Congo deep-sea fan reflects increased erosion in equatorial Africa, under the influence of wet climate, whereas establishment of an arid climate over SW Africa induced a drastic decrease of denudation rate, and thus reduced sedimentation on the margin. Neogene emplacement of the African superswell beneath southern Africa was responsible for renewed onshore uplift on both margins, but it accelerated erosion only in the Congo catchment, due to wetter climatic conditions. Neogene high sedimentation rate reactivated gravitational tectonics that had remained quiescent since late Cretaceous.

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Imaging exhumed lower continental crust in the distal Jequitinhonha basin, Brazil

Loureiro

Schnürle

Klingelhöfer

et al. 2018

Journal of South American Earth Sciences

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Twelve combined wide-angle refraction and coincident multi-channel seismic profiles were acquired in the Jequitinhonha-Camamu-Almada, Jacuípe, and Sergipe-Alagoas basins, NE Brazil, during the SALSA experiment in 2014. Profiles SL11 and SL12 image the Jequitinhonha basin, perpendicularly to the coast, with 15 and 11 four-channel ocean-bottom seismometers, respectively. Profile SL10 runs parallel to the coast, crossing profiles SL11 and SL12, imaging the proximal Jequitinhonha and Almada Please note that this is an author-produced PDF of an article accepted for publication following peer review. The definitive publisher-authenticated version is available on the publisher Web site. basins with 17 ocean-bottom seismometers. Forward modelling, combined with pre-stack depth migration to increase the horizontal resolution of the velocity models, indicates that sediment thickness varies between 3.3 km and 6.2 km in the distal basin. Crustal thickness at the western edge of the profiles is of around 20 km, with velocity gradients indicating a continental origin. It decreases to less than 5 km in the distal basin, with high seismic velocities and gradients, not compatible with normal oceanic crust nor exhumed upper mantle. Typical oceanic crust is never imaged along these about 200 km-long profiles and we propose that the transitional crust in the Jequitinhonha basin is a made of exhumed lower continental crust. Highlights ► The transitional domain in the Jequitinhonha basin is, at least, 150 km wide. ► The transitional crust is composed of exhumed lower continental crust. ► Necking occurs within less than 100 km. ► An anomalous velocity zone is imaged at the base of the crust.

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Structure and evolution of adjoining segments of the West African margin determined from deep seismic profiling

Cited by 18 publications

References 4 publications

Crustal breakup and continent-ocean transition at South Atlantic conjugate margins

Crustal breakup and continent-ocean transition at South Atlantic conjugate margins

South Atlantic continental margins of Africa: A comparison of the tectonic vs climate interplay on the evolution of equatorial west Africa and SW Africa margins

Imaging exhumed lower continental crust in the distal Jequitinhonha basin, Brazil

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