Tectonothermal evolution of the ultrahigh temperature metapelites in the Rauer Group, east Antarctica

The Mg-Al-rich Mather Paragneiss in the Rauer Group experienced three distinct stages of tectonothermal evolution: (1) An initial pre-peak stage at 10-11 kbar and similar to 850 degrees C followed by prograde heating that converted kyanite to sillimanite, and partial melting that produced coarse-grained garnet-orthopyroxene-bearing leucosomes, at similar to 12 kbar and 960-970 degrees C. (2) Initial near-isothermal decompression to similar to 10 kbar and similar to 1000 degrees C, resulting in the development of corona textures of orthopyroxene+sapphirine on garnet grains and sapphirine/orthopyroxene-K-feldspar-dominated leucosome pockets or sapphirine-orthopyroxene-cordierite-bearing leucosome stringers. (3) Subsequent decompression-cooling to similar to 7 kbar and similar to 800 degrees C involving the development of symplectic sapphirine+cordierite, orthopyroxene+cordierite and biotite+cordierite. The proposed P-T path suggests that the Mather Paragneiss had a shared P-T history with the Filla Paragneiss, with prograde P-T stage evolving in the kyanite stability field. The recognization of kyanite in stage (1), together with the peak ultrahigh temperature metamorphic event, is probably related to late Mesoproterozoic collision and arc accretion (similar to 1100-1000 Ma) that was overprinted by decompression-cooling and retrograde metamorphism during the early Palaeozoic (similar to 500 Ma) tectonic event. (c) 2006 Elsevier B.V. All rights reserved.