Abstract The thorough interpretation of the South Atlantic long offset seismic lines provides a new view of the magmatic and crustal architecture and of the evolution of the conjugate volcanic passive margins (VPM) along the austral segment of the South Atlantic Ocean. In this study, we make the synthesis of previously published and unpublished seismic profiles that are reinterpreted consistently, and, for the first time, displayed in a conjugate view. The seaward dipping reflector sequences (SDR) expose here three main structural types (inner, outer and intermediate) that can be distinguished based on both the curvature of the reflectors and the topography displayed at their downdip terminations. We observe a specific correlation between the thinning profile of the crust and the geometric attributes of SDR. This correlation suggests a genetic relationship that is discussed in-term of rheological evolution of the crust during the magma-assisted lithospheric break-up. The South Atlantic margins architecture also featured a moderate but significant asymmetry, with a relative difference estimated to about 60% for the margin width, the total volume of SDR and their spatial distribution. A change toward a more symmetric architecture is however observed when approaching the highly magmatic area of conjugate Walvis Ridge and Rio Grande Rise. The influence of the pre-rift inheritance, the mode of rifting and the coeval mantle dynamic are put into balance to explain this global architecture. In the asymmetric domain, the extrusive sequences show evidences for westward rift jumps that participate to develop a wider margin on the African side. We propose that an asymmetric thermal structure controlled by the profile of the lithosphere asthenosphere boundary may have promoted the formation of a wider African margin. The focusing of the last rift axis is associated to the development of the thickest SDR wedges above an ultimate necking zone of the crust. Conversely to the early stages of the rift which appears segmented and diachronous, the final localization of the tectono-magmatic activity appears coarsely synchronous, at least, along the northern half of the austral segment. A further higher thermal gradient than elsewhere associated to a thicker and a weaker preexisting continental crust and a more intense magmatic input is inferred to have promote the development of symmetric and very wide conjugate margins close to the Walvis Ridge and Rio Grande Rise.

中文翻译：

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南大西洋南部共轭火山被动边缘——建筑与开发

摘要 对南大西洋长偏移距地震线的彻底解释为研究南大西洋南部段的岩浆和地壳结构以及共轭火山被动边缘（VPM）的演化提供了新的视角。在这项研究中，我们对先前发表的和未发表的地震剖面进行了合成，这些剖面经过一致重新解释，并首次以共轭视图显示。向海倾斜的反射层序列 (SDR) 在这里揭示了三种主要的结构类型（内部、外部和中间），可以根据反射层的曲率和在其下倾终端处显示的地形进行区分。我们观察到地壳变薄剖面与 SDR 的几何属性之间存在特定的相关性。这种相关性表明在岩浆辅助岩石圈破裂期间地壳流变演化方面讨论的成因关系。南大西洋边缘结构也具有中等但显着的不对称性，边缘宽度、SDR 总体积及其空间分布的相对差异估计约为 60%。然而，当接近共轭沃尔维斯岭和里奥格兰德隆起的高岩浆区时，观察到一种更对称的结构变化。前裂谷继承、裂谷模式和同时期地幔动力学的影响被平衡来解释这种全球架构。在不对称域中，喷出序列显示了向西裂谷跳跃的证据，这些跳跃参与在非洲一侧形成了更广泛的边缘。我们提出，由岩石圈软流圈边界剖面控制的不对称热结构可能促进了更广泛的非洲边缘的形成。最后一个裂谷轴的聚焦与地壳最终颈缩区上方最厚的 SDR 楔形的发展有关。与裂谷的早期阶段相反，裂谷的早期阶段看起来是分段的和历时的，构造岩浆活动的最终定位似乎大致同步，至少在南半球段的北半部。比其他地方更高的热梯度与更厚和更弱的先前存在的大陆地壳和更强烈的岩浆输入有关，被推断促进了沃尔维斯海岭和里奥格兰德海隆附近对称和非常宽的共轭边缘的发展。