ICW .Fitzsimons Department of Geology and Geophysics, University of Edinburgh, The Grant Institute, West Mains Road, Edinburgh EH9 3JW,UK
ABSTRACT Metapelitic migmatites at Brattstrand Bluffs, East Antarctica, preserve granulite assemblages and a complex deformational history. Crystallized granitic melt accounts for ~25% of exposed rocks, and was produced by biotite dehydration-melting reactions in the host metapelite. Variable degrees of melt production and extraction resulted in a range of bulk compositions in the residual metapelite, from quartz-rich migmatites to restitic quartz-absent pelite. Decompressional reaction textures indicate ~11 km of exhumation after peak metamorphism at P-T conditions of ~6 kbar and ~860oC. Decompression occured during a single cycle of partial melting and melt crystallization at ~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 melting in the Himalaya and elsewhere, but melting at Brattstrand Bluffs was ultimately driven by the tectonic perturbation and subsequent thermal relaxation responsible for high metamorphic temperatures. Exhumation did not drive melting reactions, but it is likely that the presence of melt focused deformation in the migmatites and thus promoted exhumation.
KEY WORDS. decompression; exhumation; granulite; melting; migmatite
Pages:
395 -414
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