U-PB ZIRCON AGE OF THE METAVOLCANIC ROCKS OF FISHER MASSIF (PRINCE CHARLES MOUNTAINS, EAST ANTARCTICA)

Fisher Massif is believed to represent less metamorphosed portions of an extensive Proterozoic mobile belt, and is composed of metavolcanic rocks of different compositions and numerous intrusive bodies. U-Pb da ting of six zircon fractions recovered from metavolcanic rocks of inte rmediate to acidic compositions defines growth time at c.1300 Ma with prominent Pb losses at 364 Ma and in recent time. Grain morphologies d o not provide unequivocal genetic evidence, but an igneous origin for the grains studied is the most probable. The dates obtained probably r eflect igneous activity be co-eval with mafic dyke emplacement event e lsewhere in ancient East Antarctic cratonic blocks.