Asymmetric continental deformation during South Atlantic rifting along southern Brazil and Namibia |
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| Institution: | 1. Institut für Geowissenschaften, Johannes Gutenberg-Universität Mainz, 55128 Mainz, Germany;2. School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom;1. School of Geography, Geology & Environment, Kingston University, Penrhyn Road, Kingston upon Thames KT1 2EE, UK;2. Camborne School of Mines, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9FE, UK;3. Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK;4. Department of Earth and Planetary Sciences, Birkbeck College, Gower Street, London WC1E 7HX, UK;1. Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611, USA;2. School of Earth Sciences and Resources, China University of Geosciences Beijing, Beijing 100083, PR China;3. Department of Earth Sciences, The University of Adelaide, Adelaide, SA 5005, Australia;4. Department of Earth System Sciences, Yonsei University, Seoul 03722, Republic of Korea;1. Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia;2. ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS)/GEMOC, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia;1. Department of Earth Sciences, University of New Brunswick, Fredericton, NB, Canada;2. Barrick Gold Corporation, Montreal, BC, Canada;3. Department of Geological Sciences and Geological Engineering, Queen''s University, Kingston, ON, Canada |
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| Abstract: | Plate restoration of South America and Africa to their pre-breakup position faces the problem of gaps and overlaps between the continents, an issue commonly solved with implementing intra-plate deformation zones within South America. One of these zones is often positioned at the latitude of SE/S Brazil. However, geological evidence for the existence of a distinct zone in this region is lacking, which is why it remains controversial and is not included in all modeling studies. In order to solve this problem we present a study of multiple geological aspects of both parts of the margin, SE/S Brazil and its conjugate part NW Namibia at the time of continental breakup. Our study highlights pronounced differences between these regions with respect to Paraná-Etendeka lava distribution, magmatic dyke emplacement, basement reactivation, and fault patterns. In Namibia, faults and dykes reactivated the rift-parallel Neoproterozoic basement structure, whereas such reactivation was scarce in SE/S Brazil. Instead, most dykes, accompanied by small-scale grabens, are oriented margin-perpendicular along the margin from northern Uruguay to São Paulo. We propose that these differences are rooted in large-scale plate movement and suggest a clockwise rotation of southern South America away from a stable northern South America and Africa, in a similar way as proposed by others for a Patagonian continental section just prior to South Atlantic rifting. This rotation would produce margin-parallel extension in SE/S Brazil forming margin-perpendicular pathways for lava extrusion and leading to the asymmetric distribution of the Paraná-Etendeka lavas. NW Namibia instead remained relatively stable and was only influenced by extension due to rifting, hot spot activity, and mantle upwelling. Our study argues for significant margin-parallel extension in SE/S Brazil, however not confined to a single distinct deformation zone, but distributed across ~ 1000 km along the margin. |
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