Summary
Outcrops in southern Prydz Bay comprise interleaved paragneiss and orthogneiss with high-temperature mineral assemblages and structures initially regarded as 1000 Ma in age (Grenvillian), but now known to largely reflect metamorphism and deformation at ~500 Ma (Pan African). The paragneiss preserves no conclusive evidence of earlier metamorphism, but the orthogneiss has local relics of high-grade metamorphism at 1000 Ma. The Pan-African event involved crustal thickening and burial of the paragneiss to 7–9 kbar (30–35 km), followed by exhumation to 2–3 kbar (~10 km). Peak temperatures of 800–850°C were attained at ~535 Ma relatively early in the exhumation history (P = 6–7 kbar), and the rocks cooled to ~300°C by ~490 Ma (P = 2–3 kbar). The high temperatures probably reflect significant thinning of the mantle lithosphere beneath the thickened crustal pile. Exhumation was associated with pervasive fabric development and kinematic evidence for both extension and compress ion. However, the net exhumation indicates that extension was dominant and that exhumation was at least in part driven by extensional collapse of the orogen. This record of Pan-African tectonism has important implications for the consolidation of East Gondwana, which is traditionally regarded as complete by 1000 Ma.