The geology and geochemistry of the Straumsnutane Formation, Straumsnutane, western Dronning Maud Land, Antarctica and its tectonic setting on the western margin of the Kalahari Craton: Additional evidence linking it to the Umkondo Large Igneous Province

The study focuses on whole-rock major and trace element chemistry, as well as radiogenic isotope data from the Straumsnutane Formation lavas in western Dronning Maud Land, Antarctica. The data are compared with those from the Espungabera Formation lavas of central Mozambique, published data from the Borgmassivet intrusions in Dronning Maud Land, Antarctica and other intrusions in southern Africa which are correlated with the approximately 1100 Ma Umkondo Igneous Province. Petrographical studies indicate that the Straumsnutane lavas are dominated by plagioclase, clinopyroxene, amphibole and Fe-Ti oxides. Secondary mineral assemblages include chlorite, pumpellyite, white mica and epidote, indicating that the Straumsnutane lavas have been metamorphosed under low-grade greenschist-facies conditions followed by retrograde prehnite-pumpellyite- facies conditions. The chemical data for the Straumsnutane Formation lavas are dominantly tholeiitic and basaltic andesitic in composition, and indicate that they are of continental origin. Trace element ratio values for the Straumsnutane lavas suggest that fractional crystallization and/or crustal contamination have been significant processes in the magma evolution. Low to high ⁸⁷Sr/⁸⁶Sr isotopic ratios (0.682-0.720) are evident from the Straumsnutane lavas suggesting varying degrees of hydrothermal alteration/low-grade metamorphism. The calculated ⁸⁷Sr/⁸⁶Sr values and the negative 1Nd values at 1100 Ma suggest contamination by older continental crust during the genesis of the Straumsnutane Formation lavas. Isotopic modelling shows that the Straumsnutane lavas may have been formed from the mixing of a mid-ocean ridge basalt (MORB)-like source with approximately 4% of older crust similar to the Messica Granite Gneiss of central Mozambique. Comparison of the geochemical data and petrography of the Straumsnutane lavas with those of the Espungabera Formation lavas of central Mozambique shows that they are similar. Additional comparisons show that the Straumsnutane lavas are geochemically similar to rock units of the Umkondo Igneous Province in southern Africa. It is therefore concluded that the Straumsnutane Formation lavas also formed part of the Umkondo Igneous Province.