Abstract Mount Isa is a Palaeo-Mesoproterozoic terrane in Northern Australia characterized by >300 Ma of episodic tectonic activity prior to effective cratonization. This tectonic activity has resulted in dramatic changes in the heat production distribution in the crust and must have been accompanied by long-term changes in thermal regimes. Primary differentiation of crust initially enriched in heat producing elements has been achieved by felsic magmatism over much of the 300 Ma history, often associated with extensional deformation. The flux of heat producing elements from lower to mid-upper crustal levels associated with this magmatism was sufficient to cause long-term lower crustal cooling of at least 200°C. The accumulation of the radiogenic intrusives (which comprise c . 23 % of surface outcrop and have heat production rates averaging 5.2 μ Wm −3 ) in the mid-upper crust resulted in a highly stratified heat production distribution. One consequence of this distribution is that small changes in the depth to this heat production, through processes such as deformation, erosion and the deposition of sediments, lead to significant changes in deep crustal temperatures (up to 100°C) and consequently lithospheric strength. These considerations suggest that the long-term evolution of the Mount Isa region partly reflects the progressive concentration of heat-producing elements in the upper crust leading to a long-term increase in lithospheric strength, and eventually to effective cratonization. The long-term cooling and strengthening trend was locally countered by the role of subsidence during basin formation which, through burial of heat producing elements in the existing crust and the accumulation of more heat production in insulating sediments, helped to localize subsequent contractional deformation.

Abstract The Australian continent records c. 1860–1800 Ma orogenesis associated with rapid accretion of several ribbon micro-continents along the southern and eastern margins of the proto-North Australian Craton during Nuna assembly. The boundaries of these accreted micro-continents are imaged in crustal-scale seismic reflection data, and regional gravity and aeromagnetic datasets. Continental growth (c. 1860–1850 Ma) along the southern margin of the proto-North Australian Craton is recorded by the accretion of a micro-continent that included the Aileron Terrane (northern Arunta Inlier) and the Gawler Craton. Eastward growth of the North Australian Craton occurred during the accretion of the Numil Terrane and the Abingdon Seismic Province, which forms part of a broader zone of collision between the northwestern margins of Laurentia and the proto-North Australian Craton. The Tickalara Arc initially accreted with the Kimberley Craton at c. 1850 Ma and together these collided with the proto-North Australian Craton at c. 1820 Ma. Collision between the West Australian Craton and the proto-North Australian Craton at c. 1790–1760 Ma terminated the rapid growth of the Australian continent.

Abstract Recent plate tectonic models advocate assembly of Proterozoic Australia by tectonic processes that involved large-scale horizontal motions, whereas previous models suggested that the continent evolved as an essentially intact block of lithosphere. Geological and geochemical observations alone are insufficient to test whether the major cratonic blocks of Australia were together or widely separated during the Proterozoic; only palaeomagnetism can provide quantitative constraints on relative plate motions during the Precambrian. Despite deficiencies in the palaeomagnetic record for Proterozoic Australia, groups of overlapping palaeopoles for 1.7–1.8 and 1.5–1.6 Ga permit the North and West Australian cratonic assemblages to have occupied their present relative positions since at least c. 1.7Ga, and to have been joined to the South Australian cratonic assemblage since at least c. 1.5Ga. Nonetheless, additional geological, geochronological and palaeomagnetic data are required to test whether large oceans closed between any of the continental blocks.