Deformation and fluid flow in the Huab Basin and Etendeka Plateau,NW Namibia |
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| Institution: | 1. Institut für Geowissenschaften, Johannes Gutenberg-Universität Mainz, Johann-Joachim-Becher Weg 21, 55128 Mainz, Germany;2. School of Geographical and Earth Sciences, University of Glasgow, Glasgow, G12 8QQ, United Kingdom;1. Faculty of Science and Technology, Bournemouth University, Talbot Campus, Fern Barrow BH12 5BB, UK;2. Institute of Aging and Chronic Disease, University of Liverpool, Sherrington Building, Ashton Street, Liverpool L69 3GE, UK;3. Appalachian State University, 033 Rankin Science West, 572 Rivers Street, Boone, NC 28608, United States;4. Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, PO WITS, Johannesburg 2050, South Africa;1. Department of Earth Sciences, Institute of Architecture and Earth Sciences, Ferhat Abbas University, Setif 1, Campus El Bez, Setif 19137, Algeria;2. Emerging Materials Research Unit, Ferhat Abbas University, Setif 1, Campus El Bez, Setif, 19137, Algeria;3. UMR Géoazur, Université Côte d''Azur, Observatoire de la Côte d’Azur, 250 rue Albert Einstein, Sophia Antipolis, France;1. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1-3, 24148 Kiel, Germany;2. Institute of Geosciences, Kiel University, Ludewig-Meyn-Str. 10, 24118 Kiel, Germany;3. Institute of Mineralogy and Petrography, Universität Hamburg, Grindelallee 48, 20146 Hamburg, Germany;1. Department of Earth & Planetary Sciences, McGill University, QC H3A 0E8, Canada;2. School of Earth & Ocean Sciences, University of Victoria, Victoria, BC V8P 5C2, Canada;3. Department of Earth & Planetary Sciences, Harvard University, Cambridge, MA 01238, USA |
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| Abstract: | The Lower Cretaceous Twyfelfontein sandstone formation in the Huab Basin in NW Namibia shows the effects of volcanic activity on a potential reservoir rock. The formation was covered by the Paraná-Etendeka Large Igneous Province shortly before or during the onset of South-Atlantic rifting. Deformation bands found in the sandstone trend mostly parallel to the continental passive margin and must have formed during the extrusion of the overlying volcanic rocks, indicating that their formation is related to South-Atlantic rifting. 2D-image porosity analysis of deformation bands reveals significant porosity reduction from host rock to band of up to 70%. Cementation of the sandstone, linked to advective hydrothermal flow during volcanic activity, contributes an equal amount to porosity reduction from host rock to band when compared to initial grain crushing. Veins within the basaltic cover provide evidence for hot fluid percolation, indicated by spallation of wall rock and colloform quartz growth, and for a later low-temperature fluid circulation at low pressures indicated by stilbite growth sealing cavities. Sandstone samples and veins in the overlying volcanic rocks show that diagenesis of the Twyfelfontein sandstone is linked to Atlantic rifting and was affected by both hydrothermal and low-thermal fluid circulation. |
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| Keywords: | Deformation bands Cataclastic bands syn-volcanic faulting Quartz veins Porosity analysis South Atlantic rifting |
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