Petrology of early Palaeozoic lamprophyres from Schirmacher Oasis, east Antarctica

Lamprophyre dykes are conspicuous within the Proterozoic high-grade metamor phic rocks of Schirmacher Oasis. These dykes have been classified chemicall y into alkaline and calc-alkaline types on the basis of K2O/Na2O ratio and CIPW norm. The close association, age and geochemical similarities of both the lamprophyres and melasyenite in the area indicate their consanguinity a nd derivation from same source region. These lamprophyres have a high conce ntration of incompatible elements like Ba, Rb, Sr and Zr. These rocks also have a high Mg# and depict a negative Ta-Nb-Ti anomaly. The chondrite norma lised REE patterns show fractionated trends with Large Variation in LREE an d small variation in HREE concentration in both the rock groups. The calc-a lkaline lamprophyre is more enriched in LREE than the alkaline lamprophyre. It is proposed that metasomatised phlogopite-bearing enriched mantle source has undergone partial melting to generate lamprophyric magma. This magma i s generated in a continental within-plate tectonic setting. The collision o f East and West Gondwana during Pan-African orogeny, resultant overthickeni ng of continental lithosphere and generation of widespread magmatic activit y in the region due to partial melting has culminated in the intrusion of l amprophyres around 450 Ma ago.