Architecture of a Palaeoproterozoic Rift System: evidence from the Fiery Creek Dome Region, Mt Isa terrane

The Mt Isa Rift Event is a Palaeoproterozoic intracontinental extension event that defines the beginning of sedimentation into the Isa Superbasin in the Western Fold Belt, Mt Isa terrane. In the mildly deformed Fiery Creek Dome region, on the northwest flanks of the Mt Isa Rift, elements of the Mt Isa Rift Event rift architecture are preserved without being intensely overprinted by later deformation. In this region two discrete generations of northwest-dipping normal faults have been identified. Early generation normal faults were active during the deposition of fluvial and immature conglomerate and sandstone of the Bigie Formation. Renewed rifting and the development of late-generation normal faults occurred during deposition of shallow-marine sandstone and siltstone of the lower Gunpowder Creek Formation. Differential uplift between tilt blocks formed an array of spatially and temporally discontinuous synrift unconformities on the crests of uplifted tilt blocks. Applying the domino model yields similar to 28% crustal extension for the entire Mt Isa Rift Event. Northwest-striking transverse faults facilitated differential displacement along normal faults and formed boundaries to normal fault segments, creating smaller depositional compartments along half-graben axes. Three large domes were formed during laccolith emplacement. These domes produced palaeogeographical highs that divided the region into sub-basins and were a source for the coarse fluvial synrift sequences deposited during the early Mt Isa Rift Event. The basin architecture in the Fiery Creek Dome region is consistent with northwest-south east-directed extension.