New SIMS U-Pb age on zircon from the Epembe carbonatite dyke, NW Namibia: Implications for Mesoproterozoic evolution of carbonatites at the southern margin of the Congo Craton

Abstract

The Epembe carbonatite dyke is situated approximately 80 km north of Opuwo, NW Namibia. The 10 km long dyke is dominated by massive and banded sövitic carbonatite intrusions. Two types of sövite have been recognized: (1) coarse-grained light grey Sövite I which occurs in highly brecciated and fractured zones and (2) medium to fine-grained Sövite II which hosts significant concentrations of pyrochlore and apatite. The contact zone between the carbonatite and basement gneisses is marked by K-feldspar fenite. Zircons from Sövite II were dated with Secondary Ion Mass Spectroscopy (SIMS) yielding a concordia intercept age of 1184 ± 10 Ma (MSWD = 0.65, Pof = 0.42) corresponding with the weighted mean 207Pb/206Pb age of 1173 ± 12 Ma (N = 20, MSWD = 1.2) as the crystallization age for the Epembe carbonatite. Our result presents a slightly older age than previously published data for the Swartbooisdrif ferrocarbonatites about 35 km to the east of Epembe. As calcitic carbonatites usually represent the early magmatic phase during the evolution of carbonatite magmas, the calcitic and ferrocarbonatite veins linking the two carbonatite suites at the southern margin of the Kunene Intrusive Complex (KIC), suggests that the spatially associated sövitic and ferrocarbonatite dykes are genetically related and form part of carbonatite melts emplaced about 180 Ma after the KIC magmatic event.