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Evolution of the South Atlantic: Consequences for the Walvis Ridge/Rio Grande Rise (hot spot?) volcanism

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Jokat, W. , Planert, L. , Fromm, T. , Ryberg, T. , Weber, M. and Behrmann, J. (2012): Evolution of the South Atlantic: Consequences for the Walvis Ridge/Rio Grande Rise (hot spot?) volcanism , 46th Brazilian Geological Congress, Santos, Brasilien, 30 September 2012 - 5 October 2012 .
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Abstract:

Abstract The evolution of the South Atlantic in space and time is in general presented as a two plate system, where the separation of the two continent might be caused by the Tristan Hotspot. Evidence for massive subaerial and submarine volcanism is found on both margins and adjacebt basins. Namely, the Parana (Brasil) and Etendeka (Namibia) flood basalts onshore, and the Walvis Ridge and Rio Grande offshore are evidences for a long term volcanism related to the rift/drift of both continents. In science it is currently under debate, if hotspot volcanism is the driving force for the continental breakup or are e.g. the above mentioned features a by-product of the anyhow moving plates. Aeromagnetic investigations along East Antarctica show that from the beginning of the Gondwana breakup the South American and Africa plates moved in different directions and with different speeds. This most likely caused rifting along old zone of weakness between South America and southern Africa. The ridge in combination with the large igneous provinces (Etendeka and Parana) in South America and Namibia is today considered to be a classical model for hotspot driven continental break-up. For understanding the role of mantle plumes during continental breakup a large-scale geophysical experiment in 2011 on/offshore Namibia was conducted to investigate the crustal/upper mantle structure both under the Walvis Ridge and northern Namibia. Several seismic profiles in the strike and across the Walvis Ridge with in total more than 160 oceanbottom seismometers, magnetic telluric station were deployed. Onshore the number of instruments was more than 300 to map in detail the continent-ocean transition zone to enhance our understanding on how the crust was modified by the thermal anomaly. In addition, a larger number of seismological stations are operated both on- and offshore to investigate the structure of the upper mantle. Here, we reported the first results of this experiment and discuss some implications.

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