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

Abstract

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 ~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-southeast-directed extension.

Dyke swarms as indicators of major extensional events in the 1.9–1.2Ga Columbia supercontinent

“…Furthermore later cover and poor aeromagnetic data resolution have obfuscated detection of any possible passive margin overprinted by an orogen to the northeast of the swarm. A period of NW-SE directed rifting at ca 1725-1690 Ma in the Mount Isa Inlier termed the Mount Isa Rift event (Plumb et al, 1990;O'Dea et al, 1997;Betts et al, 1998Betts et al, , 1999 is potentially an intracratonic rift event related to the generation of the passive margin proposed above.…”

Overcoming Proterozoic quartzite sand-body miscorrelations: integrated sequence stratigraphy and SHRIMP U–Pb dating of the Surprise Creek Formation, Torpedo Creek and Warrina Park Quartzites, Mt Isa Inlier

“…Long-lived tectonic activity with uplift and erosion along the north-northeast-trending Mt Gordon Fault Zone is indicated. Betts et al (1999) interpreted similar relationships along northeast-trending faults in the Fiery Creek Dome area to the north (FCD on Figure 1) as synrift unconformities on the crests of uplifted tilt blocks. They noted this is consistent with northwest -southeast-directed extension during the period when the Bigie to Gunpowder Creek Formations were deposited.…”

“…We attempted to measure at least one continuous section in what we thought were likely to be the various structural compartments. Based on previous interpretations (O'Dea et al 1997;Betts et al 1999) these appear to be defined by the main northeast-trending and west-to northwest-trending faults shown on Figure 1. Detailed stratigraphic logs for each of the sections measured in the study are given in Jackson et al (2002).…”

“…Prior to the Isan Orogeny these faults probably trended closer to west -east (Betts & Lister 2001). Several integrated regional structural and stratigraphic studies in the Mt Isa Inlier contain observations on the Surprise Creek Formation, especially on its structural setting and evolution (Batson 1991;Richards 1996;O'Dea et al 1997a, b;Betts et al 1998Betts et al , 1999. On a regional scale these studies interpreted asymmetric stratal geometries for the Surprise Creek Formation, the underlying Bigie Formation and overlying Gunpowder Creek Formation, to indicate deposition into evolving east-to southeast-thickening half-grabens, bounded by north-to northeast-trending normal growth faults.…”

“…rocks younger than about 1725 Ma (Jackson et al 2000a). An 'episodic rift -sag' model characterised by repeated and widespread half-graben development (O'Dea et al1997a, b;Betts et al 1998Betts et al , 1999 and a 'strike-slip' model (Southgate et al 2000b), where sedimentation in the Gun Supersequence is related to strike-slip and oblique movements along northwest-and northeast-trending faults with the development of localised sub-basins. Betts and Lister (2001) reviewed the structural and stratigraphic evidence for these contrasting models and concluded that the inferred architecture for the strike-slip model correlates poorly with the observed structural elements and that it does not explain the regional-scale patterns of basin subsidence.…”