Relict clinopyroxenes from metadolerites of the Early Permian Petroi Metabasalt formation, studied by electron microprobe, show a limited compositional range near the diopside-augite boundary in the pyroxene quadrilateral. Clinopyroxene analyses from three metadolerites, grouped in approximately equal Fs contents, define an overall smooth trend between Fs10 and Fs16. This is typical of clinopyroxenes from mildly alkaline basic magmas. Pyroxene stoichiometry suggests high Fe3+ contents (0.04 to 0.20 a.f.u.), which with high Al (0.10 to 0.31 a.f.u.) and Ti (0.03 to 0.08 a.f.u.) implies that CaTiAl2O6 and CaFe3+AlSiO6 are important ‘other components’. Relative Alz in CaFe3+AlSiO6 decreases and consequently CaTiAl2O6 increases with progressive fractionation. This, with the Fe2+:Fe3+ ratios in the Petroi clinopyroxenes, suggests falling ƒO2 in the magma with fractionation. The ƒO2 controlled entry of Alz, Tiy and Nax into the clinopyroxenes and hence the Petroi clinopyroxene trend.

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-apaite, 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.