Southern Australia and the northwestern United States used to be neighbours.

That's what a study of Tasmania's oldest rocks has revealed.

Minerals present in rocks in the island state's north, and dating from an ocean more than 1.3 billion years ago, contain traces of minerals monazite and zircon.

University of Tasmania researchers dated the minerals and found a pattern common to sedimentary rocks from the US states of Montana and Idaho and parts of Canadian province British Columbia.


The result was "a strong genetic fingerprint and evidence" that Tasmania's Rocky Cape was geographically close about 1.4 billion years ago to a basin that stretches through parts of Canada and the US, lead researcher Jacqueline Halpin said.

She said Tasmania and North America were at the time both part of a supercontinent, Nuna, which was broken up by tectonic plate movement creating a large sedimentary basin.