Conjugate volcanic passive margins in the austral segment of the South Atlantic - Architecture and development
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...
| Published in: | Earth-Science Reviews |
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| Main Authors: | , , , , |
| Format: | Text |
| Language: | English |
| Published: |
Elsevier
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| Subjects: | |
| Online Access: | https://doi.org/10.1016/j.earscirev.2020.103461 https://archimer.ifremer.fr/doc/00744/85631/90785.pdf https://archimer.ifremer.fr/doc/00744/85631/ |
| Summary: | 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 In this study, we make the synthesis of previously published and unpublished seismic profiles that are reinterpreted consistently, and, for the first time, displayed in a conjugate view.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 ... |
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