Paleostress evolution of the Outer Kwanza basin (offshore Angola); comparison with the Congo basin and implications for the tectonic history of the Central segment of the West Africa passive margin

IF 2.2 4区 地球科学 Q2 GEOSCIENCES, MULTIDISCIPLINARY Journal of African Earth Sciences Pub Date : 2024-08-13 DOI:10.1016/j.jafrearsci.2024.105382
Boubacar Bah , Olivier Lacombe , Nicolas E. Beaudoin , Pierre-Alexandre Teboul , Jean-Pierre Girard , Claude Gout
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Abstract

This study aims at reconstructing the paleostress history of the Outer (offshore) Kwanza basin (West African passive margin) and at comparing it to stress results acquired further north in the Congo basin. Three oriented borehole cores provided by TotalEnergies and reaching the syn-rift, Barremian-Aptian pre-salt carbonates offshore Angola were investigated. Paleopiezometry based on the Stylolite Roughness Inversion Technique (SRIT) and Calcite Twin Inversion Technique (CSIT) was combined with fracture analysis, U–Pb geochronology of carbonates and burial modelling to unravel the orientations and magnitudes of horizontal and vertical stresses affecting the pre-salt carbonates over time. Calcite twins were measured from a primary sparite matrix, and the inversion process unravelled a polyphase stress history, comprising ∼ E-W and NE-SW extensional trends that we associate to the rifting (130-112 Ma) that led to the opening of the South Atlantic ocean. The ∼ E-W extension is consistent with the early occurrence of N-S striking normal faults which developed in relation to the reactivation of inherited basement structures. This ∼ E-W extension evolved during the Barremian-Aptian (?) into the dominant regional NE-SW extension marked by large-scale NW-SE striking normal faults. The stress history also comprises compressional and strike-slip stress regimes associated with a ∼N-S trending σ1 which can be related to the transfer of orogenic stresses from the distant Africa-Eurasia plate boundary at ∼67-60 Ma. Finally, compressional and strike-slip stress regimes associated with a ENE-WSW to ∼E-W trending σ1 dominated since at least ∼17-15 Ma (possibly ∼34 Ma); they are interpreted as the expression of the mid-Atlantic ridge push. These (paleo)stress results are compared and combined with earlier paleostress reconstructions in the northern offshore Lower Congo basin (also belonging to the Central segment of the margin) and in the onshore Congo basin in order to refine the stress record and the timing of tectonic events since the early Cretaceous, thus providing unprecedented constraints on the tectonic history of the West Africa passive margin. This tectonic history includes both extensional and compressional events, and was driven mainly by far-field stresses, either gravitational or tectonic in origin, which are related to interactions between the African plate and surrounding plates.

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外宽扎盆地(安哥拉近海)的古应力演化;与刚果盆地的比较以及对西非被动边缘中部地段构造史的影响
本研究旨在重建外(近海)宽扎盆地(西非被动边缘)的古应力历史,并将其与刚果盆地更北端获得的应力结果进行比较。由道达尔能源公司(TotalEnergies)提供的三个定向钻孔岩芯被用于研究安哥拉近海同步断裂的巴里米亚-中古前盐碳酸盐岩。基于苯乙烯岩粗糙度反演技术(SRIT)和方解石孪晶反演技术(CSIT)的古压强测量与断裂分析、碳酸盐岩的铀-铅地质年代和埋藏模型相结合,揭示了随着时间的推移影响盐前碳酸盐岩的水平和垂直应力的方向和大小。从原生榍石基质中测量了方解石孪晶,反演过程揭示了多相应力历史,包括东西向和东北-西南向延伸趋势,我们将其与导致南大西洋开辟的断裂(130-112 Ma)联系起来。东-西向延伸与早期出现的北-南走向正断层相一致,这些正断层的形成与继承的基底构造的重新激活有关。这种东西向延伸在巴里米亚-安普顿(?)时期演变为区域性的东北-西南向延伸,以大规模的西北-东南走向的正断层为标志。应力历史还包括与北-南走向σ1相关的压缩和走向滑动应力机制,这可能与67-60Ma∼时来自遥远的非洲-欧亚板块边界的造山应力转移有关。最后,与ENE-WSW至∼E-W走向的σ1有关的压缩和走向滑动应力机制至少从∼17-15 Ma(可能是∼34 Ma)起就占主导地位;它们被解释为大西洋中脊推力的表现形式。这些(古)应力结果与早先在下刚果盆地北部近海地区(也属于边缘中部地段)和刚果盆地陆上地区的古应力重建结果进行了比较和组合,以完善自早白垩世以来的应力记录和构造事件发生的时间,从而为西非被动边缘的构造历史提供了前所未有的制约因素。这一构造历史包括伸展和压缩事件,主要由远场应力驱动,无论是重力应力还是构造应力,都与非洲板块和周围板块之间的相互作用有关。
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来源期刊
Journal of African Earth Sciences
Journal of African Earth Sciences 地学-地球科学综合
CiteScore
4.70
自引率
4.30%
发文量
240
审稿时长
12 months
期刊介绍: The Journal of African Earth Sciences sees itself as the prime geological journal for all aspects of the Earth Sciences about the African plate. Papers dealing with peripheral areas are welcome if they demonstrate a tight link with Africa. The Journal publishes high quality, peer-reviewed scientific papers. It is devoted primarily to research papers but short communications relating to new developments of broad interest, reviews and book reviews will also be considered. Papers must have international appeal and should present work of more regional than local significance and dealing with well identified and justified scientific questions. Specialised technical papers, analytical or exploration reports must be avoided. Papers on applied geology should preferably be linked to such core disciplines and must be addressed to a more general geoscientific audience.
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