THE TIMING OF RIFT INITIATION BETWEEN THE NORTH AUSTRALIA AND GAWLER/ SOUTH AUSTRALIA CRATONS
This retrospective study searched for dated markers that might be aligned across the rift between the G/SAC and the NAC. The “Hoatson, D.M., Claoue-Long, J.C., Jaireth, S, Australian Proterozoic Mafic-Ultramafic Magmatic Events: Sheet 1, GA, Canberra” map, demarcates a deep westward embayment of the Tasman Line that delineates the rift, separating Cambrian basement from Precambrian basement, with the labeled magmatic events on either side of the rift. This is the core of the study. When the research pointed towards a PC/C boundary date, the Acraman Impact ~585ma, an integral part of the G/SAC was researched for evidence of movement.
It was found that seven Mafic-Ultramafic events realign when G/SAC is rotated counterclockwise to a position adjacent to the NAC. The Skipworth Event ~575ma was the youngest separated event. The age of the Moorilyanna Graben dropping at the narrow angle of the rift is ~550ma, coeval to the Petermann Orogeny ~550-535ma. The age of the rift floor as defined by the Tasman Line is Cambrian age or younger and confirmed by drill cores. Evidence was found that the Acraman Impact ~585ma moved with the Gawler Craton equal to the distance of the rift movement. A best fit angle finds the pivot point of the G/SA Craton movement centered in the Amadeus Basin near both the Musgrave Province, the focus of the Petermann Orogeny and a proposed large impact MAPCIS ~545ma.
Conclusions: The timing constraint for the initiation of the rift between the NAC and the G/SAC is consistent with the Neoproterozoic to Cambrian transition. The stimulus for rift initiation may be related to the coeval Neoproterozoic Petermann Orogeny (~550-535ma) or MAPCIS~545ma which are located west of the rift near to the pivot point. Field research is needed to validate these findings.