METAPELITIC MIGMATITES FROM BRATTSTRAND BLUFFS, EAST ANTARCTICA - METAMORPHISM, MELTING AND EXHUMATION OF THE MID-CRUST

Metapelitic migmatites at Brattstrand Bluffs, East Antarctica, preserv e granulite assemblages and a complex deformational history. Crystalli zed granitic melt accounts for similar to 25% of exposed rocks, and wa s produced by biotite dehydration-melting reactions in the host metape lite. Variable degrees of melt production and extraction resulted in a range of bulk compositions in the residual metapelite, from quartz-ri ch migmatites to restitic quartz-absent pelite. Decompressional reacti on textures indicate similar to 11 km of exhumation after Peak metamor phism al P-T conditions of similar to 6 kbar and similar to 860 degree s C. Decompression occurred during a single cycle of partial melting a nd melt crystallization at similar to 500 Ma, and was synchronous with tectonic unroofing of the Brattstrand Bluffs migmatites along ductile shear zones. Exhumation has been proposed as a cause of dehydration m elting in the Himalaya and elsewhere, but melting at Brattstrand Bluff s was ultimately driven by the tectonic perturbation and subsequent th ermal relaxation responsible for high metamorphic temperatures. Exhuma tion did not drive melting reactions, but it is likely that the presen ce of melt focused deformation in the migmatites and thus Promoted exh umation.