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

Abstract

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–N 2 O–CaO–K 2 O–FeO–MgO–Al 2 O 3 – SiO 2 –H 2 O–TiO 2 –Fe 2 O 3 (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.