GEOCHEMISTRY AND ORIGIN OF MESOPROTEROZOIC METAVOLCANIC ROCKS FROM FISHER MASSIF, PRINCE-CHARLES-MOUNTAINS, EAST ANTARCTICA

Fisher Massif consists of Mesoproterozoic (c.1300 Ma) lower amphibolit e-facies metavolcanic rocks and associated metasediments, intruded by a variety of subvolcanic and plutonic bodies (gabbro to granite). It d iffers in both composition and metamorphic grade from the rest of the northern Prince Charles Mountains, which were metamorphosed to granuli te facies about 1000 m.y. ago. The metavolcanic rocks consist mainly o f basalt, but basaltic andesite, andesite, and more felsic rocks (daci te, rhyodacite, and rhyolite) are also common. Most of the basaltic ro cks have compositions similar to low-K island are tholeiites, but some are relatively Nb-rich and more akin to P-MORB. Intermediate to felsi c medium to high-K volcanic rocks, which appear to postdate the basalt ic succession, have calc-alkaline affinities and probably include a si gnificant crustal component. On the present data, an active continenta l margin with associated island are was the most likely tectonic setti ng for generation of the Fisher Massif volcanic rocks.