Asymmetrical magnetic fabrics in the Egersund doleritic dike swarm (SW Norway) reveal sinistral oblique rifting before the opening of the Iapetus |
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| Institution: | 1. Département de Géologie, Université de Liège, Quartier Agora, Allée du Six Août 12, 4000 Liège, Belgium;2. UMR-CNRS 6112, Laboratoire de Planétologie et Géodynamique, Université de Nantes, 2 Rue de la Houssinière, 44322 Nantes Cedex 3, France;3. Faculté de Sciences et Technologie, Université de La Rochelle, Avenue M. Crépeau, 17402 La Rochelle Cedex 1, France;1. Graduate School of Science and Engineering, Kagoshima University, Kagoshima, 890-0065, Japan;2. Department of Safety Systems Construction Engineering, Kagawa University, Takamatsu, 761-0396, Japan;1. Department of Geoscience, Aarhus University, 8000 Aarhus C, Denmark;2. Maersk Oil Copenhagen, Denmark;3. dGB Earth Sciences, Houston, USA;1. Dép. de Géologie, Faculté des Sciences, Université Moulay Ismail, BP. 11201 Zitoune, Meknès, Morocco;2. Dpto. de Física, Escuela Politécnica Superior, Universidad de Burgos, Avd Cantabria S/N, 09006 Burgos, Spain;3. Dpto. de Ciencias de la Tierra, Facultad de Ciencias, Universidad de Zaragoza, 50009 Zaragoza, Spain;4. Dpto.de Geologia y Geoquimica, Facutad de Ciencias, Universidad Autónoma de Madrid, Calle Francisco Tomás y Valiente, 7, Ciudad Universitaria de Cantoblanco, 28049 Madrid, Spain;5. Instituto Geológico y Minero de España, Unidad de Zaragoza, C/ Manuel Lasala 44, 9B, 50006 Zaragoza, Spain |
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| Abstract: | The 616 ± 3 Ma (Ediacaran) Egersund doleritic dike swarm cuts across the Rogaland anorthosite province and its granulitic country rocks, in SW Norway. The structure of eight out of eleven main dikes of the swarm was investigated using the anisotropy of magnetic susceptibility (AMS) technique. Thermomagnetic data and values of the bulk magnetic susceptibility reveal a magnetic mineralogy dominated by Ti-poor titanomagnetite. Magnetic fabric and global petrofabric are coaxial, except in sites strongly affected by hydrothermal alteration, as demonstrated through image analysis. Asymmetrical dispositions of the magnetic foliation and lineation support the existence of a syn-emplacement, sinistral strike-slip shearing resolved on dike walls. Such asymmetrical fabrics are attributed to a transtension tectonic regime, in a context of oblique extension during the continental rifting phase which preceded the opening of the Iapetus Ocean along the SW margin (present-day orientation) of Baltica. |
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| Keywords: | Ediacaran Dolerite Rogaland Anisotropy of magnetic susceptibility Transtension Tornquist zone |
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