The Palaeoproterozoic Isa Superbasin represents an intracontinental extensional basin that began at approximately 1708 Ma during a period of approximately NW-SE directed extension (Mount Isa Rift Event). Crustal extension and tectonic subsidence were focussed along the Mount Isa Rift where 3-5 km of clastic syn-rift sequences were deposited. On the rift flanks, in the northern Mount Isa terrane periods of depositional hiatus or episodic uplift and erosion indicating a more stable uplift/subsidence history are indicated by a thinner syn-rift stratigraphy (750-2000 m).
The Mount Isa Rift was characterised by a relatively high ß1 stretching factor and a low ß2 value, and the western rift flanks and the northern Mount Isa terrane were characterised by a relatively low ß1 value and a high ß2. The distribution of syn- and post-rift sequences throughout the Isa Superbasin, and the location of syn-rift magmatic provinces, suggests that the locus of crustal extension was offset from sub crustal lithospheric thinning and asthenospheric upwelling. Such a lithospheric structure is consistent with asymmetric lithospheric extension. Granite emplacement and bimodal volcanism is confined to the northwest and west of the Mount Isa Rift. These magmatic provinces are interpreted to occur above the position of significant sub-crustal lithospheric thinning and asthenospheric upwelling, or voluminous underplating during the Mount Isa Rift Event.
Dissipation of the thermal anomalies beneath the northern Mount Isa terrane caused a shift in the basin depocentre to the northern Mount Isa terrane. Shallow marine carbonate sequences and then deeper water sediments were deposited into a sag basin. The northern Mount Isa terrane marks the position of maximum sub crustal extension during the Mount Isa Rift Event.
Elevated geothermal gradients caused by sub-crustal lithospheric thinning to the west of the Mount Isa Rift may have provided the driving force for large scale fluid flow in the Isa Superbasin. Increased thermal subsidence may have produced ideal chemical conditions for precipitating metals during hydrothermal activity. Gravity driven fluid flow would be directed to the northern Mount Isa terrane during the sag-phase evolution of the Isa Superbasin. A combination of these conditions may explain the high density of large Pb-Zn-Ag orebodies hosted within the Isa Superbasin to the west of the Mount Isa Rift.