Cooperation partners: BGR Hannover, GFZ Potsdam, University of Frankfurt, University of Goettingen

Description:

The primary aim of the off- and onshore activities along the passive margin of Namibia is the investigation of the rift-related volcanic-magmatic processes associated with the Early Cretaceous continental breakup and the separation of South Africa and South America. Continental flood basalts like the Paran flood basalts in South America and the Etendeka flood basalts on the African side are indications for plume-related volcanic margins. Supplementary paired hot spot tracks like the Walvis Ridge and the Rio Grande Rise give faith in the assumption that rifting was influenced by igneous processes. Furthermore during earlier investigation seaward dipping reflectors interpreted as volcanics are already mapped on both sides of the South Atlantic. The following work is supposed to give a better understanding of the tectonic evolution of the margin and to prove evidence for a volcanic rifted margin in the south-western part of Africa.

Therefore three profiles across the continental margin were investigated achieving simultaneous off- and onshore wide-angle data as well as offshore multi-channel seismic reflection data (see Figure 1). Additionally magnetic data was carried out as well. Complemented by already existing gravity data, information on reflectivity, seismic velocity, density and magnetic susceptibility should be evolved. The seismic data were acquired during a marine survey in 1995 by the R/V Polar Queen and the R/V Academik Nemcinov.

The two northernmost profiles (BGR 95-R I, BGR 95-R II) are already processed by Klaus Bauer (K. Bauer et al., 2000). The third southernmost profile (BGR 95-R III) has not been processed completely by now. The reflection data has been stacked and partly migrated but the wide-angle data is still incompletlely processed.

This work which is supposed to be done within the next year is the following:

• raytracing by using 6 ocean bottom hydrophones offshore and 20 land-stations onshore Namibia
• further processing of reflection data in order to achieve a better resolution of the upper crust and to determine the geometry of the sediment basin to improve the raytracing model
• generating a 2D gravity model to enhance the reliability of the model and especially the continent-ocean boundary
• compilation of a crustal section

With this work it should be proven if typical features of volcanic margins like seaward dipping reflectors and may be underplating can also be found farther south of the Namibia continental margin. A comparision and interpolation between the two northerly profiles and southern one is to be envisaged as well as figuring out the differences.

Figures: