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In marked contrast to Palaeoproterozoic Laurentia, the location of sutures and boundaries of discrete crustal fragments amalgamated during Palaeoproterozoic formation of the North Australian Craton remain highly speculative. Interpretations of suture locations have relied heavily on the analysis of regional geophysical datasets because of sparse exposure of rocks of the appropriate age. The Mount Isa Fault Zone has been interpreted as one such Palaeoproterozoic terrane-bounding suture. Furthermore, the coincidence of this fault zone with major shale-hosted massive sulphide Pb–Zn–Ag orebodies has led to speculations that trans-lithospheric faults may be an important ingredient for the development of this deposit type. This study has integrated geophysical and geochemical data to test the statute of the Mount Isa Fault as a terrane-bounding suture. Forward modelling of gravity data shows that basement rocks on either side of the Mount Isa Fault have similar densities. These interpretations are consistent with geochemical observations and Sm–Nd data that suggest that basement lithologies on either side of the Mount Isa Fault are geochemically and isotopically indistinguishable from each other, and that the Mount Isa Fault is unlikely to represent a suture zone that separates different Palaeoproterozoic terranes. Our data indicate that the crustal blocks on both sides of the Mount Isa Fault Zone must have been in within close proximity of each other since the Palaeoproterozoic, and that the Western Fold Belt was part of the (ancestral) North Australian Craton well before the ∼1.89–1.87 Ga Barramundi Orogeny. It appears that deep crustal variations in density may be related to the boundary between a shallowly west-dipping high-density mafic to ultramafic plate and low-density basement rocks. This interpretation in turn impacts on crustal-scale models for the development of shale-hosted massive sulphide Pb–Zn mineralisation, which do not require trans-lithospheric faults to tap deep-seated metal reservoirs and/or mantle plumbing systems. The approach applied herein demonstrates the value of multi-disciplinary investigations to the critical assessment of long-lived Proterozoic fault systems which, in the absence of methodical analysis, are commonly assumed to represent terrane-bounding sutures. [Copyright &y& Elsevier]

The basement rocks in central Queensland are largely obscured by the Phanerozoic sedimentary succession and direct information comes only from sparse geological data. 2.5D forward modelling of regional aeromagnetic and Bouguer gravity data has been undertaken to unveil the crustal architecture at the junction of the Proterozoic Mount Isa terrane and the Phanerozoic Thomson Orogen in Queensland. The most prominent geophysical character is represented by the abrupt termination of positive NNW-trending geophysical anomalies of the Mount Isa terrane against NE-trending, low amplitude gravity and magnetic anomalies of the Diamantina River Domain of the Thomson Orogen. Potential field forward modelling indicates that the lower basement crust of the Thomson Orogen is petrophysically indistinguishable from the crust of the Proterozoic Mount Isa terrane. We interpret that the prominent gradients associated with the Cork Fault represent the displacement and burial of the Mount Isa terrane crust under the Thomson Orogen. In this context, the Cork Fault is inferred to represent a fundamental crustal discontinuity but does not represent the eastern margin of Rodinia because the Thomson Orogen is floored by Precambrian continental crust. Initiation of the Cork Fault might have occurred as early as the Mesoproterozoic. At that time, the Cork Fault was a major structure that developed during the separation of the Mount Isa terrane and the Curnamona Province. It is inferred that this break-up occurred during initial N-S to NNW-SSE extension. The Cork Fault formed part of a network of major north- and south-dipping normal faults active at that time. The Cork Fault was repeatedly reactivated during the Neoproterozoic Rodinia break-up and during the Phanerozoic evolution of the Tasmanides. We suggest that the segment of the inferred ‘Tasman Line’ along the southern termination of the Mount Isa terrane should be regarded as a set of structures offsetting the Proterozoic crust rather than a simple lineament dividing the Proterozoic and the Phanerozoic Australian continent. [ABSTRACT FROM AUTHOR]