Research progress of the ultrahigh-temperature granulites in the Rauer Group, East Antarctica

Abstract

The Rauer Group (Rauer Islands), located in the eastern margin of the Prydz Tectonic Belt in East Antarctica, represents a composite high-grade metamorphic terrane consisting of Archaean and Mesoproterozoic rocks. The Mesoproterozoic rocks contain Fe-Al-rich garnet-sillimanite-bearing Filla Paragneiss associations, and have experienced two phases of metamorphism involving Grenvillian and Pan-African events. The Archaean orthogneisses contain Mg-Al-rich sapphirine-bearing ultrahigh-temperature (UHT) pelitic granulite associations (Mather Paragneiss associations), and they consist mainly of sapphirine-bearing pelitic granulite, Mg-rich garnet-sillimanite-bearing pelitic paragneiss, orthopyroxene-sillimanite quartzite, garnet-bearing mafic granulite and calcsilicate granulite that experienced ultrahigh-temperature metamorphism. In the sapphirine-bearing pelitic granulite, typical post-peak decompression textures around garnet porphyroblasts and sillimanite aggregations (kyanite pseudomorph) developed as symplectite assemblages consisting of sapphirine-orthopyroxene and sapphirine-cordierite respectively. In the garnet-bearing mafic granulite, typical post-peak 'white-eye socket' decompression texture on garnet porphyroblast also developed as symplectite composed of orthopyroxene-plagioclase. Until recently, different researchers derived distinct-type clockwise P-T paths of various peak UHT conditions and pre-peak and post-peak evolution histories, whereas different opinions also exist regarding the timing of UHT metamorphic event and tectonic setting. For example, a UHT metamorphic event was considered to occur either during the Grenvillian period (~1000 Ma) associated with a collisional orogenesis and arc magmatism or during the Pan-African period (~590 Ma or~530 Ma) related to the Prydz orogenesis and the Gondwana continent assembly. Thus, in order to clarify the metamorphic evolution history and tectonic setting of the UHT granulites in the region, further detailed studies on analyses of the mineral assemblages and metamorphic textures and the reconstruction of P-T path as well as high-precesion zircon and monazite U-Pb chronological dating are needed, and regional geological comparison should also be undertaken.

Keywords

• ultrahigh-temperature granulites
• metamorphic p-t paths
• research progress
• rauer group
• east antarctica