首页> 外文期刊>Journal of African Earth Sciences >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
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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

机译:非洲南大西洋大陆边缘:构造与气候相互作用对赤道西非洲和西南非洲边缘演化的比较

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摘要

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, syn-rift 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.
机译:非洲显示出各种大陆边缘结构,构造样式和沉积记录。对两个代表性部分的比较回顾:赤道西部非洲边缘和非洲西南非洲边缘,有助于分析影响这些边缘发展的主要控制因素。沃尔维斯山脊以南的早白垩世活跃裂谷导致了西南非洲火山边缘的形成,该火山边缘显示出厚而宽的中间火成地壳,与未伸展的厚大陆壳相邻。沃尔维斯山脊以北的非火山裂谷模式导致了赤道西非边缘的形成,其特征是地壳伸展和变薄的区域很宽,并且形成了厚而广泛的同裂谷盆地。裂谷后早期的对比岩性(盐对页岩)决定了重力变形的方式,而挠曲作用的活动期则受沉积速率控制。在西南白垩纪至始新世期间,非洲西南部突出的肩部隆升的回归侵蚀造成了高碎屑沉积速率,而赤道西非陆架的主要碳酸盐产量表明,低腹地的侵蚀很少。渐新世早期的长期气候变化在两个边缘都形成了对比。大量陆生刚果深海扇的进入反映了在潮湿气候的影响下赤道非洲的侵蚀加剧,而非洲西南部干旱气候的建立导致剥蚀率急剧下降,从而减少了边缘的沉积。南部非洲下方非洲超隆的新近纪侵袭是造成两个边缘再次陆上隆升的原因,但由于气候条件较湿,它仅在刚果流域加速了侵蚀。新近纪高沉积速率重新激活了自白垩纪晚期以来一直保持静止的重力构造。

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