Björnnutane and Sembberget basalt lavas and the geochemical provinciality of Karoo magmatism in western Dronning Maud Land, Antarctica
Geochemical provinciality of the Karoo continental flood basalt (CFB) province is complicated by the great diversity of magma types. Our geochemical and Nd and Sr isotopic data indicate derivation of Karoo-related low-Ti CFBs of Björnnutane and Sembberget, Dronning Maud Land, Antarctica, from different magma plumbing systems that were typified by generation of magma subtypes largely by variable degrees of fractional crystallization and crustal contamination. We associate these plumbing systems with different mantle sources and propose that the Karoo CFBs of Dronning Maud Land can be grouped into two provinces derived from these sources. The Grunehogna province magmas include high-Ti and some low-Ti magma types, have high (Sm/Yb)N (> 2), are enriched in Sr and Eu, and show wide range of initial εNd (+ 9 to − 16). Grunehogna province magmas dominate at Björnnutane, Vestfjella, and Ahlmannryggen. The Maud province magmas show low-Ti affinity, have low (Sm/Yb)N (< 2), lack Sr and Eu enrichment, and have relatively narrow range of initial εNd (+ 3 to − 4). Maud province magmas are restricted to Sembberget, Kirwanveggen and the Utpostane gabbros in Vestfjella. The enrichment of Sr and Eu and the depletion of heavy rare earth elements in Grunehogna province magmas, and, specifically, geochemical indications of recycled oceanic crust in the least-contaminated high-Ti and low-Ti basalts and picrites lend support to a recycled source component. Grunehogna magmas are ascribed to partial melting of eclogite-bearing asthenospheric mantle source at depth below the Grunehogna craton and contamination of the magmas with lithospheric mantle (high-Ti types) and crust (low-Ti types). The Maud province magmas can be ascribed to relatively low-pressure partial melting probably of a lithospheric mantle source within the zone of rifted lithosphere associated with the Weddell triple junction and lateral flow of magmas to present outcrops overlying thick Maud Belt lithosphere. Geochemical comparison with Karoo CFBs in southern Africa implies a broadly similar division between the high-Ti and low-Ti magma types associated with the Limpopo structure and the low-Ti magma types of the Central Area and Botswana.
Authors: Luttinen, Arto V., Leat, Philip T., Furnes, Harald