Metamorphic and tectonic evolution of granulites, Arunta Block, central Australia

Abstract

Petrographical and chemical evidence presented here indicate a prolonged metamorphic evolution of the granulite terrain in the northern Strangways Range, Arunta Block, central Australia (NSR in Fig. 1), beginning with migmatization, followed by dry granulite metamorphism at high temperatures (T) and moderate pressures (P) (estimated at 850–920 °C, 8±1 kbar¹). This occurred at ∼1,800 Myr (refs 2, 3), very shortly after deposition of the protolith⁴, a bimodal volcanic suite⁵ and associated sediments. Granulite metamorphism was followed by isobaric cooling, during which there was an episode of pervasive but partial hydration. Later retrogression and hydration, localized along shear zones, occurred at the normal geothermal gradient in the kyanite stability field. A tensional, rift-like regime best describes the geological environment in which the protolith formed, was deeply buried, metamorphosed with high heat flow, and then remained in isostatic equilibrium. Metamorphic parageneses recording uplift may be matched with mid-Palaeozoic tectonic events in central Australia. If this correlation is correct, the rocks of the northern Strangways Range may have remained deeply buried for 1,400 Myr, during which the shear zones were reactivated several times (Fig. 2).