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Geodynamic model for the Weddell Sea using aeromagnetic and palaeomagnetic data

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König, M. (2003): Geodynamic model for the Weddell Sea using aeromagnetic and palaeomagnetic data , Workshop, East-West Antarctic Tectonics and Gondwana Breakup 60W-60E,13 Sept., Potsdam, Bremen. .
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Abstract:

The results of a new aeromagnetic compilation for the Weddell , Lazarev and Riiser-Larsen Sea, joining the EMAGE (East-Antarctic Margin Aeromagnetic and Gravity Experiment, Jokat et al. 2003), USAC (U.S. Argentina Chile, LaBrecque et al. 1989) and shipborne magnetic data from the NGDC (National Geophysical Data Center, Boulder, Colorado), give refined constraints on the early development of the Weddell Sea and adjacent areas during the initial stages of Gondwana break-up.Clear coast parallel sea floor spreading anomalies off the west coast of Dronning Maud Land and another pattern of clearly discernible spreading anomalies in the Riiser-Larsen Sea could be used for magnetic modelling. This led to a well constrained age model from the beginning of seafloor spreading in the Riiser-Larsen Sea at ca. 155 Ma and the eastern Weddell Sea at about 144 Ma to the final separation of South America from Africa about 130 Ma ago. The linear trend of the magnetic anomalies together with their detailed age determination allowed the calculation of new rotation poles for the times when Antarctica and Africa began to drift away from their Early Jurassic position within Gondwana and South America and Antarctica separated through the opening of the Weddell Sea.For the Early Jurassic no constraints on the position of East- and West-Gondwana (Antarctica, Madagascar, India, Australia and South America, Africa) and the West Antarctic microplates (Antarctic Peninsula - AP, Ellsworth-Withmore Mountains block,Thurston Island block, Mary Byrd Land) can be derived from magnetic seafloor spreading anomalies since no ocean floor exists from this period. For these times palaeomagnetic pole positions give the best information about palaeogeography.Palaeomagnetic poles from Grunow (1993, 1999) show relative movements of the Antarctic Peninsula and the other West-Antarctic microplates just prior and during the early opening of the Weddell Sea. In these models the AP forms the southern continuation of the Permo-Triassic subduction zone of South America. With partly large movements of the different blocks between 200 Ma and 130 Ma. The model presented by Jokat et al. 2003 based on mainly aermagnetic data suggests a far southerly position of South America for this period with the AP beeing fixed to the East Antarctic craton.An advanced model will be presented combining the results based on dating of magnetic seafloor spreading anomalies and palaeomagnetics and trying to adjust the different views of the early history of Gondwana break-up and the development of the Weddell Sea.References:Grunow, A.M., 1993: Creation and destruction of Weddell Sea floor in the Jurassic. Geology, v. 21, p 647-650.Grunow, A.M., 1999: Gondwana events and palaeogeography: a palaeomagnetic review. Journal of African Earth Siences, Vol. 28, No. 1, pp 53-69.Jokat, W., Boebel, T., König, M., Meyer U., 2003: Timing and Geometry of Early Gondwana Break-Up, Journal Geophysical Research, (in press).LaBrecque, J.L., Bronzena J., Parra, J.C., Keller, M.A., Haxby, W., Raymond, C.A., Kovaks, L., Bell, R., Yanez, G., Peters, M., Cande, S., Valladares, J., 1989: USAC Aerosurvey Results for the Weddell Basin: Part I. 28th International Geological Congress, Washington, DC, USA.

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