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• Sedimentary rocks can record the assembly and breakup of supercontinents. • Ancient North America (Laurentia) assembled by 1.7 billion years ago. • 1.4 billion year old rocks in western N. America were sourced from Australia. • Australia was likely connected to western N. America after 1.7 billion years ago. • Australia likely broke away from western N. America 1.3 billion years ago. Rocks of the Gold Cup Quartzite, Belt Supergroup and Deer Trail Group crop out in the Priest River region of northeastern Washington and northern Idaho (USA). As these sequences represent the westernmost exposures of Paleoproterozoic–Mesoproterozoic strata between New Mexico (USA) and the northern Yukon (Canada), they are key to understanding the assembly of Laurentia and evaluating the duration and configuration of the supercontinent Nuna/Columbia. Here, we present detrital zircon U–Pb and Lu–Hf isotope data from these sequences. The results indicate that the <1.73 Ga Gold Cup Quartzite contains similar detrital zircon components to other widespread late Paleoproterozoic units that record final assembly of the main Archean blocks of western Laurentia; as such, they do not require any non-Laurentian source. Prominent ca. 1.7–1.5 Ga, isotopically juvenile zircon grains form the main component of the overlying ca. 1.47 Ga Lower Belt Supergroup. Some of these detrital zircon components lack a Laurentian source and are instead consistent with derivation from the Gawler Craton in southeastern Australia. The >1.38 Ga upper Belt Supergroup strata are structurally overlain by <1.3 Ga Deer Trail Group rocks that contain detrital zircon components consistent with mixed Laurentian sources. The paucity of any syndepositional volcanic detrital zircon in Deer Trail Group strata along with its fine siliciclastic and carbonate nature suggest deposition within a tectonically-quiescent basin coeval with breakup of Nuna. [ABSTRACT FROM AUTHOR]

• Theoretical cumulative zircon growth models presented. • Comparison of cumulative Ti-in-zircon & models quantifies disequilibrium growth. • Malthusian parameter (R) characterizes cumulative zircon growth curve. • More sigmodal (higher R) growth curves imply greater crystal-liquid segregation. We generate theoretical curves for zircon growth during cooling of tonalitic and A-type granitic magmas and compare these with empirical Ti-in-zircon populations from the Paleoarchean Pilbara Craton, Australia, Mesoarchean Akia Terrane, Greenland, and the Mesoproterozoic Musgrave Province, Australia. Our models predict variable zircon growth rates on magma cooling dependant on magma composition, crystallizing assemblage, and zircon growth process. In most modelled magma compositions, higher-temperature grains growing close to the zircon saturation temperature are more abundant, with yields decreasing continuously thereafter. However, there are important dissimilarities in the cumulative zircon growth curve for different magma compositions and whether zircon growth is by equilibrium or disequilibrium processes. For a given starting melt Zr concentration, A-type granite magmas grow zircon at higher temperatures than tonalitic magmas. This compositional distinction is most pronounced at lower starting melt Zr concentrations, and in low Zr tonalite the rate of zircon growth may even increase on cooling. The dependence of zircon growth on magma composition and crystallization process leads to predictive differences in cumulative Ti-in-zircon distributions. Greater disequilibrium growth yields more sigmoidal cumulative growth curves that are dissimilar to predictions from phase equilibrium models. When applied to Mesoarchean-aged zircon grains from the Akia Terrane, calculated Ti-in-zircon temperatures decrease over the 3100–2900 Ma interval. This magmatic episode also reveals a change in cumulative zircon growth curve topology from steeper to shallower, consistent with a reduction in the relative proportion of disequilibrium growth, greater crystal–liquid communication, and enhanced infracrustal reworking. The temporal variability in cumulative zircon growth and its implication for melt interconnectedness are powerful tools in understanding magmatic processes and indicate an important secular change point at c. 3.0 Ga in the Akia Terrane where zircon growth dynamics changed. [ABSTRACT FROM AUTHOR]

• 1560 Ma TTG suite and migmatised mafic source exposed in NE Australia. • 'High-pressure' TTG generated at a depth of 25–35 km. • Field observations and trace-element modelling point to fluid-fluxed melting. • TTG chemical diversity reflects variable hydration, not depth. Across the Archaean to Proterozoic transition, the composition of newly-formed felsic continental crust changed from tonalite–trondhjemite–granodiorite (TTG) to calc-alkaline granitoid, possibly coinciding with the emergence of plate tectonics. Nevertheless, TTG suites were sporadically produced in Proterozoic and Phanerozoic orogenic belts, and such occurrences may provide petrological and tectonic insights into the formation of ancient continents. Here we demonstrate that the ca 1560 Ma Forest Home TTG plutonic suite in the Georgetown Inlier, NE Australia, was derived from partial melting of spatially-associated mafic rocks in a post-collisional setting. The studied TTG rocks have a 'high-pressure' geochemical signature, with elevated Sr, low heavy rare earth element and low high field strength element contents. Established petrogenetic models suggest they were derived by partial melting either of hydrated basaltic crust at >70 km depth or enriched lithospheric mantle, or by fractionation of lower-pressure mafic magmas. Using phase equilibrium calculations and trace-element modelling, we show that the geochemical signature of the Georgetown TTG likely resulted from fluid-fluxed crustal melting at relatively shallow depths (25–35 km), consistent with field observations and the inferred metamorphic evolution of the inlier. Our results suggest that the chemical variability of TTGs can reflect the variable availability of fluids rather than depth of melting, which has implications for tectonic processes responsible for the formation of early continental crust. [ABSTRACT FROM AUTHOR]