Representative analyses of garnet, plagioclase, orthopyroxene, ilmenite, hornblende and biotite for pre-tectonic mafic and metapelitic rocks in Gjelsvikfjella

• Main Authors: Bisnath, Avinash, Frimmel, Hartwig E
• Format: Other/Unknown Material
• Language: English
• Published: PANGAEA 2015
• Subjects: Dronning Maud Land; Antarctica; Gjelsvikfjella; Priority Programme 1158 Antarctic Research with Comparable Investigations in Arctic Sea Ice Areas; ROCK; Rock sample; SPP1158; Arctic; Antarctic; East Antarctica; Antarc*; Antarctica Journal; Sea ice
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.846974; https://doi.org/10.1594/PANGAEA.846974

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 (M1) left in strain-protected domains. Petrological and mineral chemical evidence indicates a clockwise P-T-t path for the Pan-African orogeny. Peak metamorphic (M2b) 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 (M2a). 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 (M1; 1090-1030 Ma) and again during the Pan-African orogeny (M2a, M2b) between 565 and 530 Ma. Post-peak metamorphic K-metasomatism under amphibolite-facies conditions (M2c) followed and is ascribed to post-orogenic bimodal magmatism between 500 and 480 Ma.