Thermal evolution of mafic granulites of Princess Elizabeth Land, East Antarctica

Abstract

Outcrops of East Antarctic Shield exposed along the coast of Princess Elizabeth Land (PEL) provide a peek into its Neoproterozoic evolution. The terrain comprises of interleaved pelitic, felsic and mafic granulites. Examination of mafic granulites from Sostrene Islands - Larsemann Hills - Brattstrand Bluffs terrain indicate multiple sources for their protolith. The ensemble of mafic rocks intimately associated with sedimentary protoliths are sourced from older mafic crust as well as syn-sedimentary intrusives, prior to multiple stages of deformation and high-grade metamorphism, often including felsic melt generation. High-grade metamorphism (peak conditions of ~900 °C and 11 kbar) followed by two stages of decompression, which are indicated by the presence of symplectitic growth of orthopyroxene over garnet and in cracks in garnetiferous mafic granulite. Pseudosection modelling confirms that the mafic granulites underwent a near isothermal decompression of ~2–3 kbar, indicating a clockwise PT path. Chemical dating of monazites from associated paragneisses show three growth zones viz. a Grenvillian aged core (884–940 Ma) followed by a thin Upper Tonian- Cryogenian aged middle rim (689–754 Ma) and a typical Pan African aged outer rim (523 Ma). We suggest that the thermo-tectonic evolution of PEL outcrops should be reassessed taking into account the newly emerging evidence of Tonian metamorphism.