Consequences of variable degrees of crustal contamination on the phase petrology an halogen budget of plume-related Northern Etendeka effusives and dikes, NW Namibia

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In the recent years, mafic to silicic rocks belonging to the Cretaceous Etendeka bimodal continental flood basalt 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, a series of different mafic and silicic flood volcanics is exposed (Miller, 2008). A multitude of dolerite dikes 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 volcanic and associated dike 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 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 halogen budget (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 halogen record with isotope and trace element geochemistry.