Deep depleted and shallow enriched mantle sources of Karoo CFBs: geochemical evidence from Antarctica

The Karoo continental flood basalts and associated intrusive rocks are typified by a great diversity of geochemical types that are most readily identified based on incompatible element and isotopic characteristics. The principal mantle source in the Karoo province has been frequently ascribed to lithospheric mantle, possibly affected by previous subduction-related fluids and/or melts; only a few rock types show unambiguous affinity to significant asthenospheric source components. Most recently, uncontaminated dyke rocks with depleted mantle geochemical characteristics (e.g. initial epsilon Nd values of up to +8) and strong garnet signatures have been discovered in Vestfjella, in the Antarctic extension of the Karoo CFB province. Our geochemical modeling implicates that a rich variety of low-Ti and high-Ti daughter magma types, notably similar to Karoo CFB types in Vestfjella, can be generated by contamination of a single depleted mantle-derived parental magma type with lithospheric material: We generalize that the deep depleted mantle source of the Vestfjella dykes may also have been the principal source of the numerous low-Ti and high-Ti magma types that are found within or adjacent to the Kaapvaal-Grunehogna craton in the Karoo province. In contrast, the low-Ti magma types that lack a garnet signature and are found outside the craton were derived from shallow, possibly subduction-contaminated mantle sources.