Abstract
Rb–Sr whole-rock and mineral isotope data from nepheline syenite, tinguaite, and carbonatite samples of the Kalkfeld Complex within the Damaraland Alkaline Province, NW Namibia, indicate a date of 242 ± 6.5 Ma. This is interpreted as the age of final magmatic crystallization in the complex. The geological position of the complex and the spatially close relationship to the Lower Cretaceous Etaneno Alkaline Complex document a repeated channeling of small-scale alkaline to carbonatite melt fractions along crustal fractures that served as pathways for the mantle-derived melts. This is in line with Triassic extensional tectonic activity described for the nearby Omaruru Lineament–Waterberg Fault system. The emplacement of the Kalkfeld Complex more than 100 Ma prior to the Paraná-Etendeka event and the emplacement of the Early Cretaceous Damaraland intrusive complexes excludes a genetic relationship to the Tristan Plume. The initial εSr–εNd pairs of the Kalkfeld rocks are typical of younger African carbonatites and suggest a melt source, in which EM I and HIMU represent dominant components.
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Acknowledgements
We are very grateful to A. Stracke, Münster, and K. Mezger, now Bern, for the chance to perform the isotope measurements at the lab of the Institute of Mineralogy, University of Münster. R. B. Trumbull, Potsdam, kindly provided the two critical samples KF 201 und KF 203 of Bühn and Trumbull (2003). The careful chemical work of J. Jakobi, and help during preparation of figures by M.A. Voß, both RWTH Aachen University, as well as stylistic corrections by N. Jordan, Leicester, are greatly appreciated. Constructive criticism of the reviewers B. Trumbull, Potsdam, and R.E. Harmer, Grahamstown, which significantly improved the manuscript, is gratefully acknowledged.
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Kramm, U., Körner, T., Kittel, M. et al. Triassic emplacement age of the Kalkfeld complex, NW Namibia: implications for carbonatite magmatism and its relationship to the Tristan Plume. Int J Earth Sci (Geol Rundsch) 106, 2797–2813 (2017). https://doi.org/10.1007/s00531-017-1460-2
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DOI: https://doi.org/10.1007/s00531-017-1460-2