Sequence-stratigraphic interpretations of outcrop, drillcore, wireline and seismic datasets are integrated with SHRIMP zircon and palaeomagnetic determinations to provide a detailed chronostratigraphic basin framework for the base-metal-rich Palaeoproterozoic rocks of the southern McArthur, Lawn Hill and Mt Isa regions. The analysis forms a basis for future correlations across northern Australia. Nine second-order unconformity-bounded supersequences are identified. Supersequences have a duration of 10-20 million years; some hitherto-unrecognised unconformity surfaces record up to 25 million years of missing rock record. The second-order supersequences contain a series of nested third-, fourth-and fifth-order sequences many of which can be correlated across the Mt Isa, Lawn Hill and southern McArthur regions. The analysis relates accommodation history to major intraplate tectonic events evident on the apparent polar wander path for northern Australia. Major tectonic events at approximately 1735 Ma, and 1575 Ma impacted on accommodation rates and basin shape in northern Australia. Sub-basin depocentres, the hosts for major sulfide mineralisation, are attributed to reactivated faults that controlled local subsidence. Pb/Pb model ages of 1653 Ma, 1640 Ma and 1575 Ma for the Mt Isa, McArthur River and Century Pb-Zn-Ag deposits, suggest that changes to intraplate stresses at tectonic events of like age resulted in the migration of metal-bearing fluids into the sub-basins. A Pb/Pb model age of 1675 for the Broken Hill deposit suggests that intraplate stresses manifest in northern Australia also affected rocks of similar age further south. Magmatic events close to 1700 Ma (Weberra Granite) and 1675 Ma (Sybella Granite) coincide with times of regional incision and the formation of supersequence-bounding unconformity surfaces.

Fifty-five new SHRIMP U-Pb zircon ages from samples of northern Australian 'basement' and its overlying Proterozoic successions are used to refine and, in places, significantly change previous lithostratigraphic correlations. In conjunction with sequence-stratigraphic studies, the 1800-1580 Ma rock record between Mt Isa and the Roper River is now classified into three superbasin phases-the Leichhardt, Calvert and Isa. These three major depositional episodes are separated by ~20 million years gaps. The Isa Superbasin can be further subdivided into seven supersequences each 10-15 million years in duration. Gaps in the geological record between these supersequences are variable; they approach several million years in basin-margin positions, but are much smaller in the depocentres. Arguments based on field setting, petrography, zircon morphology, and U-Pb systematics are used to interpret these U-Pb zircon ages and in most cases to demonstrate that the ages obtained are depositional. In some instances, zircon crystals are reworked and give maximum depositional ages. These give useful provenance information as they fingerprint the source(s) of basin fill. Six new 'Ma) at the top of the Isa Superbasin is essentially unconstrained. The integration of high-precision SHRIMP dating from continuously analysed stratigraphic sections, within a sequence stratigraphic context, provides an enhanced chronostratigraphic framework leading to more reliable interpretations of basin architecture and evolution.

Sequence‐stratigraphic correlations provide a better understanding of sediment architecture in the Mt Isa and lower McNamara Groups of northern Australia. Sediments record deposition in a marine environment on a broad southeast‐facing ramp that extended from the Murphy Inlier in the northwest to the Gorge Creek, Saint Paul and Rufous Fault Zones in the southeast. Depositional systems prograded in a southeasterly direction. Shoreline siliciclastic facies belts initially formed on the western and northern parts of the ramp, deeper water basinal facies occurred to the east and south. The general absence of shoreline facies throughout the Mt Isa Group suggests that depositional systems originally extended further to the east and probably crossed the Kalkadoon–Leichhardt Block. Fourteen, regionally correlatable fourth‐order sequences, each with a duration of approximately one million years, are identified in the 1670–1655 Ma Gun Supersequence. Stratal correlations of fourth‐order sequences and attendant facies belts resolve a stratigraphic architecture dominated by times of paired subsidence and uplift. This architecture is most consistent with sinistral strike‐slip tectonism along north‐northeast‐oriented structures with dilational jogs along northwest structures as the primary driver for accommodation. Although reactivated during deformation, the ancestral northwest‐ trending May Downs, Twenty Nine Mile, Painted Rocks, Transmitter, Redie Creek and Termite Range Fault Zones are interpreted as the principal synsedimentary growth structures. Sinistral strike‐slip resulted in a zone of long‐lived dilation to the north of the May Downs/Twenty Nine Mile and Gorge Creek Fault Zones and a major basin depocentre in the broad southeast‐facing ramp. Subordinate depocentres also developed on the northern side of the ancestral Redie Creek and Termite Range fault zones. Transfer of strike‐slip movement to the east produced restraining or compressive regions, localising areas of uplift and the generation of local unconformities. Northwest‐ and north‐northeast‐oriented magnetic anomalies to the south and west of Mt Isa, identify basement heterogeneities. Basement to the south and west of these anomalies is interpreted to mark intrabasin siliciclastic provenance areas in the Gun depositional system. Pb–Zn–Ag deposits of the Mt Isa valley are interpreted as occurring in a major basin depocentre in response to a renewed phase of paired uplift and subsidence in late Gun time (approximately 1656 Ma). This event is interpreted to have synchronously created accommodation for sediments that host the Mt Isa deposit, while focusing topographically and thermobarically driven basinal fluids into the zone of dilation.

A largely convergent setting is proposed for crustal, tectonic and basin evolution of the intracratonic regions of north-central Australia between 1800 and 1575 Ma. The new geodynamic model contrasts with previous proposals of widespread extension during the Leichhardt, Calvert and Isa intervals. Local transtensional to extensional structures exist, but these are best explained by a combination of flexural, thermal and dynamic processes related to an active southern margin. The development of thick accumulations of sediments (superbasins) is linked geodynamically to interpreted active margin processes (subduction and magmatic arcs) in central Australia. A synthesis of geochemical data from the 1870-1575 Ma igneous units from the Arnhem, McArthur and Mt Isa regions of north-central Australia confirms the intracratonic setting of these units and suggests that a long-lived thermal anomaly was responsible for the generation of both mafic and felsic magmas. The geochemical characteristics suggest the igneous units are derived from the lithospheric mantle and are not typical rift-or plume-related melts. A review of the U-Pb SHRIMP ages for the entire region demonstrates the minimum distribution of correlative igneous rocks was widespread. Exotic populations in the 207 Pb/ 206 Pb isotopic data provide insights into the nature and evolution of the crust throughout northcentral Australia. Archaean inheritance is found to be nearly ubiquitous. The data support the temporal subdivision of north-central Australia into the Leichhardt (1800-1750 Ma), Calvert (1750-1690 Ma) and Isa (1690-1575 Ma) intervals which are marked by superbasins and concomitant episodes of igneous activity. A highly heterogeneous pre-superbasin crust is interpreted from regional, newly processed geophysical data. The cratonic portion of north-central Australia is interpreted to consist of three broad northwest-trending belts or elements that are further distinguished into western, central and eastern geophysically distinct provinces. A map of the superbasin distribution is derived and integrated with structural and stratigraphic data to assess the evolution of the basins and the crust through time. The superbasin successions of north-central Australia are synchronous and widespread, although not necessarily interconnected. The tectonic model incorporates dynamic tilting of the craton during episodes of subduction and transmission of compressive intraplate stresses through the craton during intervening episodes of orogeny. These processes resulted in flexure, strikeslip deformation and a complex thermal structure. These mechanisms account for the subsidence and basin evolution that results in widespread ramp and strike-slip basins. The model also accounts for the thermal history recorded by magmatic events. The proposed geodynamical model provides a unifying crustal evolution scenario for central and northern Australia for approximately 225 million years of the Proterozoic.

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