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Dating the final assembly of supercontinent Nuna

1.6 Ga crustal thickening along the final Nuna suture

Precisely defining the nature and timing the collision of proto-Australia and Laurentia (North America) during the final assembly of the supercontinent Nuna has remained elusive. It has previously been speculated that this final suture zone is concealed in northeastern Australia, but definitive evidence for crustal thickening across the suture zone has been critically lacking. In our latest publication we report new garnet petrological and geochronological results of samples from both sides of the inferred suture. The precise dates (from Lu–Hf of garnet) show synchronous prograde metamorphism between 1606- and 1598-million years ago, representing crustal thickening in the Georgetown Inlier and simultaneous basin inversion in the Mount Isa Inlier. Large-scale collision is further supported by interpretation of deep seismic reflection images of the northeastern Australia continental crust.

The precisely dated collision-related processes in northeastern Australia correlate with 1.61–1.59 Ga orogenesis recorded within South Australia and North America, suggesting a large-scale collision of Laurentia with Australia–East Antarctica, and pinpointing the final assembly of the supercontinent Nuna.

Final Nuna assembly
Northeastern Australian Nuna suture. A) Present-day crustal structure adapted from Korsch et al.’s (2012) geophysical imaging and modeling. Interpreted Nuna 1.6 Ga suture separates an upper plate (Australia) with east-dipping thrusts, and a lower plate (Laurentia) with west dipping, crustal-scale faults. Symbols show locations of exposed 1.6 Ga internal orogens. B) Schematic lithospheric cross section across the Nuna suture at ca. 1.6 Ga showing the collision of the Laurentian promontory (Georgetown) to eastern North Australia (N Aus.) and bivergent far-field thrusting in Australia (Mount Isa) and Laurentia (Laur.) (Wernecke). C: Possible Nuna Australia–Antarctica Laurentia configuration at 1.6 Ga marking the final supercontinent assemblage. Presently emerged continents are shown with their possible original extensions (faded colors).

Contact person: Dr. Amaury Pourteau and Prof. Zheng-Xiang Li, Earth Dynamics Research Group, Curtin University.

Relevant publication:

Amaury Pourteau, Matthijs A. Smit, Zheng-Xiang Li, William J. Collins, Adam R. Nordsvan, Silvia Volante, and Jiangyu Li; 1.6 Ga crustal thickening along the final Nuna suture. Geology, Volume 46, Issue 11, pages 959-962 (2018). doi: 10.1130/G45198.1