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Petrogenesis of gabbroic and doleritic Etendeka rocks East of Cape Fria, NW Namibia

Principal Investigators: Dr. Gregor Markl, Dr. Thomas Wenzel

In the recent years, basaltic to rhyolithic rocks belonging to the Cretaceous Etendeka bimodal continental flood volcanic province have been intensively studied by means of major and trace element as well as radiogenic isotope geochemistry (e. g., Ewart et al. 2004a, b). All of these rocks are composed of a Tristan plume component and variable amounts of crustal contaminants. In the Northern Etendeka area, NW Namibia, where the Walvis ridge meets the continental crust, the gabbroic Cape Fria complex and a multitude of basic dykes underly or intersect the flood volcanics and are most probably temporally and chemically related to the Etendeka rocks. We plan a thorough study of these subvolcanic rocks using a combination of phase petrology, major, trace element, and stable (O, S, C) isotope geochemistry combined with the determination of F, Cl and Br. The questions to be addressed are a) the temporal and petrological connection of the Walvis Ridge, Cape Fria complex, Agate Mountains carbonatite and effusive magmatism in this area; b) the conditions of crystallization based on QUILF analyses; c) the effect of crustal contamination on rock diversity and intensive crystallization parameters; d) the resolution of spatial trends from offshore to on-shore and from North to South in the phase assemblages and intensive parameters of crystallization; e) the reconstruction of the melting regime with specific focus on the volatile content (F, Cl, Br, on whole rocks and apatite) and the stable isotope geochemistry (S on sulfides and apatite, O on Cpx and Plag, C on apatite); and f) the resolution of the mechanism of contamination (by fluids or melts, in the lower or upper crust) by comparing the volatile record with isotope and trace element geochemistry.