Assembly of proto-Australia prior to the formation of the Nuna supercontinent in the Paleoproterozoic

Kirscher, Uwe1,2, Mitchell, Ross N3,1, Liu, Yebo1, Nordsvan, Adam R4,1, Wu, Lei5,1, Pisarevsky, Sergei1, Li, Zheng-Xiang1

1Earth Dynamics Research Group, School of Earth and Planetary Sciences, The Institute for Geoscience Research (TIGeR), Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), Curtin University, Perth, Australia, 2Department of Geosciences, Eberhard Karls University of Tuebingen, Tuebingen, Germany, 3State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China, 4Department of Earth Sciences, University of Hong Kong, Pokfulam, Hong Kong, 5Department of Earth & Planetary Sciences, McGill University, 3450 Rue University, Montréal, Canada

The paleogeography, chronology and importance of the Paleoproterozoic assembly of the supercontinent Nuna are still debated. To further test the paleogeographic evolution of the Australian cratons in the leadup to Nuna formation, we present new paleomagnetic results from two Paleoproterozoic rock formations in North Australia. First, we obtained paleomagnetic directions from the 1825±4 Ma, bimodal Plum Tree Creek Volcanics sequence of the North Australian Craton (NAC). Second, we studied the 1855±2 Ma layered mafic-ultramafic ‘Toby’ intrusion from the Kimberley Craton (KC). Samples from both study areas reveal high quality, stable, magnetite related characteristic remanent magnetization directions. Combining within-site clustered mean directions, we obtained two paleopoles, which plot proximal to each other in the present day central Pacific Ocean, off the east coast of Australia. These results agree with previous interpretation that the Kimberly Craton was amalgamated with the rest of the NAC prior to ca. 1.85 Ga. Comparing these new results with slightly younger poles from the NAC and slightly older, rotated poles form the West Australian Craton (WAC) reveal a high degree of similarity suggesting minimal absolute plate motion between ca. 1.9 and 1.65 Ga. All available paleomagnetic poles agree with an assembly, or close juxtaposition, of the two major Australian cratons (NAC and WAC) before 1.8 Ga. Furthermore, the individual virtual geomagnetic poles from the potentially slow cooled Toby intrusion show a non-fisherian distribution along a great circle. This spread might be related to previously interpreted major true polar wander events based on data from Laurentian cratons, which would be global if such an interpretation is correct. The assembly of proto-Australia prior to ca. 1.85 Ga roughly 250 to 300 Myr before the final stage of supercontinent Nuna’s amalgamation ca. 1.6 Ga suggests that assembling of major building blocks, such as Australia and Laurentia for the supercontinent Nuna and Gondwana for the supercontinent Pangea, is an important step in the formation of supercontinents.


Biography

UK did his undergraduate and PhD at Ludwig-Maximilians University in Munich, Germany. He then moved to Perth for a three-years postdoc at Curtin University, before he moved back to Germany for another postdoc at Tuebingen University.

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