PETROLOGY OF CORDIERITE PLUS GEDRITE-BEARING SODIC GRANULITE FROM THEGRENVILLIAN LONG-RANGE INLIER, NEWFOUNDLAND

Sodium-rich, potassium-poor granulite in the Long Range Inlier contain s Ab + Qtz + Crd + Bt + Opx + Ilm and either gedrite or garnet, but ra rely both. The distribution of garnet in the sodic gneiss was influenc ed by bulk compositional controls (e.g., higher Al2O3/SiO2). Textural evidence indicates that gedrite was metastable with respect to Crd + O px during granulite-grade metamorphism. Peak metamorphic conditions ar e estimated to have been similar to 700 degrees C at 600 MPa; the meta morphic fluid was CO2 rich. The preservation of pelitic (Sil + Crd + B t + Grt + Qtz + Mc + And) layers in which K2O > Na2O suggests a sedime ntary precursor for the sodic gneiss, but the granulites are more sodi c and less magnesian than primary sediments recently identified as pos sible precursors to cordierite-orthoamphibole rocks (e.g., ultramafic- derived greywackes; evaporitic mudstones). Leucosomes tend to be more sodic (mean Na2O/K2O = 23.5) than mesosomes (mean Na2O/K2O = 17.8 in g arnet-free gneiss and 1.4 in garnetiferous gneiss), so, unless migmati tic melts were fractionated, the unusual composition of the sodic gnei ss cannot be attributed solely to partial melting processes. The gneis s is interpreted to be derived from a weathered greywacke.