Metamorphic conditions during formation of a metapelitic sillimanite-garnet gneiss from Clemence Massif, Prince Charles Mountains, East Antarctica

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.