Mesoproterozoic intraplate magmatism in the Kalahari Craton: a review

The Kalahari Craton was initially stabilized following cessation of Palaeoproterozoic orogenesis in southern Africa at ca. 1.8 Ga. Subsequent Mesoproterozoic intraplate magmatism at ca. 1.4–1.35 Ga formed a series of alkaline and carbonatitic complexes in the southern part of the craton. Original volcanic structures are partly preserved in some of the complexes, and a variety of intrusive rocks (e.g., quartz syenite, nepheline syenite, pyroxenite, ijolite, carbonatite) are present. The Premier kimberlite cluster was emplaced in the same region at ca. 1.2 Ga, but available geochronology indicates that the main alkaline magmatism preceded 1.2–1.0 Ga orogenesis in the Namaqua–Natal–Maud Belt along the southern craton margin. Another, more extensive intraplate magmatic event at ca. 1.1 Ga formed the Umkondo Igneous Province, which is recognized over an area of ∼2.0 × 10⁶ km² on the Kalahari Craton, including a detached fragment now located in Antarctica. Much of the province comprises high-level mafic intrusions, but erosional remnants of basalt lava piles and bimodal basalt/rhyolite assemblages are also present. Most of the mafic rocks are continental tholeiites, but trace-element geochemistry reveals distinct subgroups that cannot be related by crustal-level assimilation/fractional crystallization processes or by partial melting of a uniform mantle source. Geochronological and palaeomagnetic data indicate that enormous volumes of tholeiitic magma were emplaced within the province in a narrow time frame at ca. 1112–1106 Ma, which is inferred to record uprise of a mantle plume behind the Namaqua–Natal–Maud Belt.