Characteristics of the early remnant mineral associations in granulite-facies rocks from the Larsemann Hills, East Antarctica and their metamorphic conditions

Granulite facies pelitic gneiss and mafic granulite outcropping in the Larsemann Hills, East Antarctica, underwent a complicated deformational-metamorphic history. Early remnant D 1 structures represent a prograde thickening event which probably formed at 1000Ma (Grenvillian). In response to D 1, M 1 peak metamorphic assemblages were characterized by inclusions of cordierite and sillimanite within coarse-grained garnets or spinels in pelitic gneisses and inclusions of orthopyroxene and plagioclase within coarse-grained garnet in mafic granulites. Sapphirine-magnetite and sapphirine-spmel-sillimanite-magnetite-quartz assemblages included in coarse-grained orthopyroxene in orthopyroxene-biotite-bearing quartzite from Stornes Peninsula have been found, whilst fine-grained spinel occurs as inclusions within this sapphirine. P-T calculations suggest maximum M 1 metamorphic conditions of ��870��C and ��0. 95GPa according to garnet-orthopyroxene thermometer and garnet-orthopyroxene-plagioclase-quartz barometer. These remnant mineral associations indicate that their metamorphism takes on characteristics of anticlockwise near-isobaric cooling (IBC) P-T evolution, also reflect a prograde metamorphic formation process of prograde heating during burial. The M 1(1000Ma) anticlockwise (IBC) P-T path derived here for this area may be related to magmatic underplating beneath existing continental crust and intrusion and crystallization of substantial volumes of igneous material within crust. This type of anticlockwise P-T path is distinct from the late clockwise P-T path evolved during the 500Ma (Pan-African).