Paleomagnetism of the Hart Dolerite (Kimberley, Western Australia) – A two-stage assembly of the supercontinent Nuna?

Abstract

We present new paleo- and rock magnetic results from the ca. 1792 Ma Hart Dolerite sills that intrude the strata of the Kimberley craton, Western Australia. From 24 sites sampled, 23 are directionally clustered and the site mean directions were used to calculate a grand mean direction. Ten of the 23 sites have 95% confidence intervals (a95) less than 16°. A positive reversal test, dissimilarity of the corresponding paleopole from known younger Australian poles, and a previously reported positive baked contact test, indicate that our paleomagnetic results are of primary origin, and the results are consistent with the geologic interpretation that the Hart Dolerite sills represent a multiphase magmatic emplacement over the duration of several million years. The new ca. 1792 Ma paleopole for the Kimberley craton is applicable to the entire North Australian Craton. A comparison of Paleoproterozoic poles from the North and West Australian cratons supports the occurrence of a previously proposed 40° intracontinental rotation between the two cratons during latest Neoproterozoic time. Furthermore, comparing these Australian poles with similar aged Laurentian poles shows that the apparent polar wander paths of the two continents have a similar history between ca. 1800 and 1730 Ma and between ca. 1650 and 1400 Ma. To achieve a fit within uncertainty limits, an additional relative latitudinal motion is necessary during the transition interval (1730–1650 Ma). We suggest that a two-stage evolution occurred between Laurentia and Australia during the assembly of the supercontinent Nuna. Australia and Laurentia traveled together between ca. 1800 Ma until ca. 1730 Ma in a semi-stable configuration. During 1730–1650 Ma, they underwent a net relative latitudinal motion, leading to the final assembly of Nuna after ca. 1650 Ma.