HIGH-GRADE REWORKING OF CENTRAL AUSTRALIAN GRANULITES .1. STRUCTURAL EVOLUTION

Four distinct deformational events (D2-D5) accompanying a granulite facies metamorphic cycle (M2-M5), are shown to structurally overprint (rework) pre-existing granulites (M1) of the northeast Strangways Range in the central Arunta Block. The first metamorphic cycle (M1) at 1800 Ma, involved an anticlockwise P-T path peaking at 850-950-degrees-C at 8-9 kbar. M1 metamorphism involved widespread partial melting that produced stromitic migmatites and map-scale concordant granitic gneisses. Isobaric cooling after the peak, and accompanying hydration, gave rise to a wide variety of coronitic and symplectitic reaction textures that enclose and replace M1 mineral parageneses. No kinematic structuring is associated with M1, and the period encompassing the thermal peak and immediately subsequent are thought to have been absent of deviatoric stress. The second metamorphic cycle (M2-M5), possibly at 1400-1500 Ma, involved a clockwise P-T path with a maximum P of > 9-10 kbar and a thermal peak of approximately 800-degrees-C. This metamorphic cycle accompanied the major ductile deformations recognized (D2-D5), and has been labelled the "Proterozoic Reworking". The Proterozoic Reworking has been divided into two thermo-barometric and structurally distinct periods. D2-D3 involved regionally inclined, ENE-WSW non-coaxial shear of high bulk shear strains, giving rise to an intense (often mylonitic) perfasive fabric (S2-L2) and isoclinal and sheath folds on all scales (F2, F3). S2-L2 is the first recognized kinematic fabric and does enclose and partially recrystallize M1 mineral parageneses, including late-M1 metamorphic reaction textures. D2-D3 deformation was due to crustal shortening and gave rise to crustal over-thickening (loading) accompanying prograde metamorphism (M2). D4-D5 involved upright, open and asymmetrical folding (F4) and E-W-trending shear zone development (S5) within a regionally extensive system of inclined, oblique, sinistral transpression. Both D2-D3 and D4-D5 episodes occurred under the same approximately E-W-directed compressive stress, and are considered sequential episodes in the one tectonothermal cycle. F4 folding accompanied significant melt formation and the peak of metamorphism of the M2-M5 metamorphic cycle. S5 shear zones accompanied 3-4 kbar of decompression with cooling, presumably during uplift in isostatic response to crustal over-thickening in D2-D3. Progression from inclined non-coaxial shear to transpression occurred in response to an