Metamorphic evolution of the Maud Belt: P– T– t path for high-grade gneisses in Gjelsvikfjella, Dronning Maud Land, East Antarctica

Abstract

A metamorphic petrological study, in conjunction with recent precise geochronometric data, revealed a complex P– T– t path for high-grade gneisses in a hitherto poorly understood sector of the Mesoproterozoic Maud Belt in East Antarctica. The Maud Belt is an extensive high-grade, polydeformed, metamorphic belt, which records two significant tectono-thermal episodes, once towards the end of the Mesoproterozoic and again towards the late Neoproterozoic/Cambrian. In contrast to previous models, most of the metamorphic mineral assemblages are related to a Pan-African tectono-thermal overprint, with only very few relics of late Mesoproterozoic granulite-facies mineral assemblages (M 1) left in strain-protected domains. Petrological and mineral chemical evidence indicates a clockwise P– T– t path for the Pan-African orogeny. Peak metamorphic (M 2b) conditions recorded by most rocks in the area ( T = 709–785 °C and P = 7.0–9.5 kbar) during the Pan-African orogeny were attained subsequent to decompression from probably eclogite-facies metamorphic conditions (M 2a). The new data acquired in this study, together with recent geochronological and geochemical data, permit the development of a geodynamic model for the Maud Belt that involves volcanic arc formation during the late Mesoproterozoic followed by extension at 1100 Ma and subsequent high-grade tectono-thermal reworking once during continent–continent collision at the end of the Mesoproterozoic (M 1; 1090–1030 Ma) and again during the Pan-African orogeny (M 2a, M 2b) between 565 and 530 Ma. Post-peak metamorphic K-metasomatism under amphibolite-facies conditions (M 2c) followed and is ascribed to post-orogenic bimodal magmatism between 500 and 480 Ma.