We propose a model that places development of IOCG (and porphyry-epithermal) mineralisation at ca. 1.60-1.57 Ga in eastern Proterozoic Australia into the context of a modern-day subduction zone. The model is comparable to modern analogues of the Late Cretaceous to Early Eocene Laramide Orogeny in the western United States, present-day slab geometries in the Andes of South America, and by the formation of Cretaceous IOCG and Cu-porphyry deposits in the Chilean Coastal Cordillera. The model depicts a change from rollback subduction geometry and development of extensional basins in the overriding plate (~1.67 - 1.604 Ga) to flat-slab subduction at 1.604 Ga. The change in subduction architecture was triggered by the arrival of a buoyant oceanic plateau at the subduction site. Slab-melting and metasomatism of the subcontinental lithospheric mantle (SCLM) resulted in eclogitasation and densification of the frontal oceanic slab, slab steepening, sudden upwelling of hot asthenosphere, and production of anhydrous, F-rich, S-poor melts that interacted with the metasomatised SCLM. Resultant mafic melts underwent fractionation and eventually formed the dominantly A-type Hiltaba Suite granites and Gawler Range Volcanics and were associated with IOCG mineralisation. The downgoing slab steepened and retreated, which can be tracked by the progressive westerly to southwesterly younging direction of the Hiltaba Suite. Slab retreat resulted in further asthenospheric upwelling and progressive development of an asthenospheric wedge in a normal subduction geometry. Heat introduced from the asthenospheric wedge resulted in dehydration of buoyant oceanic lithosphere and production of S-rich fluids that interacted with the asthenosphere to produce oxidised, S-rich partial melts. Within this architecture, the spatial and temporal distribution of IOCG and porphyry-epithermal mineral systems in the Gawler Craton is dictated by the evolution of the subducting slab and the chemistry of the fluids/melts derived from the subducting slab.

Open-Access Online Publication: May 22, 2023