Geology of the Larsemann Hills, Princess Elizabeth Land, Antarctica

The Larsemann Hills region is dominated by two major lithological associations, a Mesoproterozoic to Neoproterozoic felsic dominated orthogneiss complex (Søstrene Orthogneiss) which occurs as basement to a sequence of pelitic, psammitic and felsic paragneisses (Brattstrand Paragneiss) and felsic intrusives. Recent unpublished data suggest a late Neoproterozoic depositional age for the Brattstrand Paragneiss. Current geochronology indicates that the region experienced medium to low pressure granulite-facies metamorphism during the Early Palaeozoic (~515-530 Ma). Although the paragneiss sequences record no evidence of earlier metamorphism, relics of a previous metamorphic event at ~1000-950 Ma are preserved in the Søstrene Orthogneiss. Within the Larsemann Hills region, the Early Palaeozoic event is characterised by peak metamorphism of ~7 kbar at ~800-850°C, with the post-peak evolution characterised by decompression, with some cooling, to 4 kbars at 750°C, then to 2-3 kbar at 600-650°C during final stages of orogenesis, with exhumation largely driven by crustal extension. Tectonic models generally argue for a continental-continental collisional scenario, with thermal input derived from a thinned mantle lithosphere.