Assembly of Proterozoic Australia: implications of a revised pole for the ∼1070 Ma Alcurra Dyke Swarm, central Australia

The pole position for the late Mesoproterozoic Alcurra (formerly Kulgera) Dyke Swarm (ADS), Musgrave Block, central Australia, has been revised by adding new data from two more dykes. A palaeomagnetic fold test is positive at the 99 percent confidence level and the pole position is latitude =2.8° S, longitude =80.4°E (dp =7.2°, dm =10.7°). New ⁴⁰Ar/³⁹Ar determinations on single biotite grains from country-rock gneiss 20 cm from the contact with an Alcurra dyke yield ages from 1068 ± 2 Ma to 1085 ± 2 Ma (2σ). In addition, ⁴⁰Ar/³⁹Ar determinations on two samples of aggregates of very fine-grained biotite from the mesostasis of a Stuart Dyke (SD), Arunta Inlier, Northern Territory, yield ages of 1059 ± 2 and 1066 ± 3 Ma (2σ). These new ages are in agreement with those of the ∼1070 Ma Warakurna large igneous province, west-central Australia, indicating that both the ADS and SD belong to that suite. Palaeomagnetic poles determined by others for the ADS and SD are indistinguishable from each other but cannot be presently combined as a single pole because the published information on the SD is incomplete. An analysis of the palaeogeography implied by the dispersed palaeomagnetic poles from members of the extended Warakurna suite shows that the present relationships between the major Precambrian cratons (West, North and South Australian), which constitute Australia west of the Tasman Line, are inconsistent with the inferred relationship at ∼1070 Ma. Nor is it apparent that internal deformations within the separate cratons are the cause of the dispersion. Our findings imply that these major Australian Cratons must have finally assembled sometime after ∼1070 Ma.