The pressure (P) and temperature (T) conditions during metamorphism of a metapelitic sillimanite-garnet
gneiss from Clemence Massif, Antarctic Prince Charles Mountains, are estimated using mineral abundance information
and petrogenetic P–T pseudosections computed in the chemical system MnO–N2O–CaO–K2O–FeO–MgO–Al2O3–
SiO2–H2O–TiO2–Fe2O3 (MnNCKFMASHTO). Calculated mineral equilibria for the appropriate bulk composition predict that the observed assemblage, of K-feldspar–garnet–quartz–sillimanite–biotite–ilmenite–rutile, stabilised at
approximately 8–9 kbar and 760–790ºC. Reaction microstructures are rare, but the preservation of relic spinel
inclusions in garnet indicates an earlier low-P, high-T component and possible anticlockwise path.