HIGH-GRADE REWORKING OF CENTRAL AUSTRALIAN GRANULITES - METAMORPHIC EVOLUTION OF THE ARUNTA COMPLEX

The poly-metamorphic evolution of the Strangways Range granulites of central Australia has been constrained by the phase stability relationships of silica-saturated aluminous gneisses in KFMASH, in conjunction with geothermobarometry and equilibrium thermodynamics. Two contrasting, but overlapping, P-T paths are proposed. The first(M1, at 1800 Ma) had an 'anticlockwise' P-T path (i.e., increasing P/T with time) and was terminated by isobaric cooling from 850-950-degrees-C, at 8-9 kb, to a stable crustal geotherm (< 700-degrees-C). In contrast, the second granulite metamorphism (M2-M5, suggested to be at 1400-1500 Ma; Goscombe, 1992a) followed a 'clockwise' P-T path (i.e., decreasing P/T with time) terminated by decompression and cooling to approximately 6-7 kb on a stable crustal geotherm. M2-M5 occurred during reworking of M1 granulites by compressional orogenesis (Goscombe, 1992a). Initially, loading and prograde metamorphism accompanied non-coaxial ductile shear and fold repetition (D2-D3). Prograde metamorphism was followed by uplift and retrogression accompanying oblique transpression and shear zone development while still under compression (D4-D5) (Goscombe, 1992a). The poly-metamorphic evolution indicates that ductile deformation reworked the M1 granulites in an orogenic episode unrelated, both temporally and tectonically, to M1 metamorphism (Goscombe, 1992b).