Geometry of the margins of the North Australian Craton and correlations with upper crustal structures

The margins of the North Australian Craton (NAC) are major lithospheric boundaries that correspond to zones of intense faulting in the upper crust. The sutures defining the edges of the eastern and southern margin of the NAC have different geometries. The eastern margin (Mount Isa Inlier) is characterised by a west-dipping geometry that dips toward the interior of the craton (inward), whereas the southern margin (Arunta Inlier) dips to the south away from the craton interior (outward). The causes of these different geometries are not well-understood, nor is their influence on later phases of deformation. We have used gravity, magnetic and seismic reflection data to investigate the influence of the NAC margin geometry on the distribution and connectivity of structures in the upper crust. These geophysical data were used to interpret major crustal boundaries, including major sutures and shallow structures. Three major structures occur on the eastern margin of Mount Isa Inlier: the Gidyea Suture Zone, the Pilgrim Fault Zone, and the Western Edge Fault. Each of these major structures dips towards the interior of the craton. Our interpretation reveals the presence of shallow listric structures that sole out into regional decollements, which are antithetic to the major crust-penetrating faults. We observe two major sutures along the southern margin of the Arunta Inlier: the Willowra Suture and the Warrumpi Suture. The Willowra Suture represents the southernmost edge of the NAC. Seismic reflection data reveals that the structural style is very different to that of Mount Isa. Faults in the footwall of Willowra Suture are more widely spaced and penetrate through the crust to the Moho. There is no obvious link between the geometry of this margin and upper crustal structures. By comparing these findings from the Mount Isa and Arunta Inliers we can establish relationships between the structural architecture and the geometry of the craton margin.