A METAMORPHIC PERSPECTIVE ON THE PAN-AFRICAN OVERPRINT IN THE AMERY AREA OF MAC-ROBERTSON-LAND, EAST ANTARCTICA

The Amery area of Mac. Robertson Land lies between the early Palaeozoi c granulite terrain of Prydz Bay and Meso-Neoproterozoic granulites in northern Prince Charles Mountains(nPCM). In contrast to the nPCM whic h shows an apparently simple near-isobaric history, granulites exposed in the Amery area contain reaction textures suggesting a more complex evolution. Peak-M-1 Mesoproterozoic assemblages formed at c. 700 MPa and 800 degrees C and initially underwent a near-isobaric cooling. A s ubsequent increase in temperature (M-2) resulted in the formation of c ordierite-spinel assemblages at similar to 450 MPa and 700 degrees C i n metapelite. The timing of M-2 is not firmly established, however exi sting data strongly suggest it is an early Palaeozoic event coeval wit h tectonism in Prydz Bay to the north-east. Thus the metamorphic evolu tion of granulites in the Amery area reflects a terrain-scale thermal interference pattern between two unrelated orogenic events. In rocks n ot recording post-M-1, isobaric cooling, the superposition of M-2 on M -1 assemblages resulted in the formation of M-2 cordierite-spinel symp lectites at the expense of peak M-1 garnet and sillimanite. This textu re, commonly interpreted to reflect near-isothermal decompression, has no relevance in terms of a single tectonothermal event in the Amery a rea.