Textures and assemblages developed in the quartzo-feldspathic granulites

Granulite-facies gneisses not overprinted by high-strain deformation during the Petermann Orogeny are generally coarse to medium grained, have a granoblastic texture and a dominantly anhydrous mineralogy. Peraluminous quartzo-feldspathic gneiss commonly contains the assemblage quartz + K-feldspar + garnet (Grt1; of composition Alm50-60, Prp33-45, Grs3-6, Sps2-3; abbreviations after Kretz, 1983) + plagioclase (An30) + magnetite ± biotite ± spinel ± sillimanite. Pressure estimates using the garnet-aluminosilicate-quartz-plagioclase geobarometer (GASP; Ghent, 1976) for garnet bearing quartzo-feldspathic gneiss with sillimanite inclusions range from ~7 to 8.5 kbar at 800°C (Camacho, 1997).