MagNetZ w. Uwe Kirscher (2021/11/17) - Formation of the Nuna supercontinent in the Paleoproterozoic
Channel: MagNetZ
Date: 2021-11-19

Assembly of proto-Australia during the formation of the Nuna supercontinent in the Paleoproterozoic

The video is also available for download at: https://earthref.org/ERDA/2504/
and can be referenced with the doi: 10.7288/V4/ERDA/2504

Title: Assembly of proto-Australia during the formation of the Nuna supercontinent in the Paleoproterozoic
Author: Uwe Kirscher from Department of Geosciences, University of Tübingen, Germany

It is still unclear how the supercontinent cycles initiated on Earth. Obtaining a deeper insight into the paleogeographic aspects of this mechanism will yield important boundary conditions for fundamental evolutionary transitions on Earth. Some of them are the onset of plate tectonics or the evolution of life. More evidence is emerging that the Paleoproterozoic supercontinent Nuna actually represents the first of its kind with a similar tenure and size compared to its successors Rodinia and Pangea. To add further understanding how the supercontinent cycles are related and if they are related to similar mantle processes, more data is needed on the potentially first supercontinent cycle. To address this debate, I will 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 assembly of Earth’s first supercontinent was a prolonged process and seems different compared to assembly events of later supercontinents. This together with a rather long tenure period of Nuna might indicate the initiation period of supercontinent cycles necessary for the modern plate tectonic world in the Phanerozoic.