Blueschist and eclogite in tectonic melange, Port Macquarie, New South Wales, Australia

摘要

The Rocky Beach Metamorphic Melange contains metre-scale phacoids of high-P low-T metamorphic rocks embedded in chlorite-actinolite schist. The phacoids include eclogite, glaucophane schist and omphacitite and provide evidence for four episodes of metamorphism with mineral assemblages: M₁ = actinolite-glaucophane-titanite-apatite, M₂ = almandine-omphacite-lawsonite ± quartz, M₃ = phengite-glaucophane-K-feldspar-quartz, and M₄ = chlorite-actinolite-calcite-quartz-titanite-white mica ± albite ± talc. M₁–M₃ occurred at a Neoproterozoic–Early Palaeozoic convergent plate boundary close to the eastern margin of Gondwana. Peak metamorphic conditions were attained during the static phase M₂, with temperatures of ~560°C and pressures in excess of 1.8 GPa, equivalent to a depth of burial of at least 54 km.