Isotopic constraints (Pb, Rb-Sr, Sm-Nd) on the sources of early Cambrian Pegmatites with boron and beryllium minerals in the Larsemann hills, Prydz Bay, Antarctica

Abstract

The Brattstrand Paragneiss, a highly deformed Neoproterozoic granulite-facies metasedimentary sequence, is cut by three generations of ∼500 Ma pegmatite. The earliest recognizable pegmatite generation, synchronous with D2-3, forms irregular pods and veins up to a meter thick, which are either roughly concordant or crosscut S2 and S3 fabrics and are locally folded. Pegmatites of the second generation, D4, form planar, discordant veins up to 20-30 cm thick, whereas the youngest generation, post-D4, forms discordant veins and pods. Clear associations of pegmatites with broadly coeval granites are lacking. The D2-3 and D4 pegmatites are abyssal class (boron-beryllium subclass) characterized by g..