Australasian Science: Australia's authority on science since 1938

The Big Twist

By Zheng-Xiang Li

Fossil magnetic needles in ancient Australian rocks have revealed that the continent underwent a 40° twist that split apart its most famous mineral provinces.

Zheng-Xiang Li is professor in geology and geophysics at the Institute for Geoscience Research, Curtin University.

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Everyone knows that the Australian continent is old and flat. Being such a vast and flat continent means there has been little tectonic activity within the continent for a very long time. In fact, the last major mountain-building event in Australia occurred more than 100 million years ago (Ma) along the continent’s younger east coast.

However, geological records reveal that this vast and peaceful continent, made of pits and pieces of continental blocks or fragments of various ages, had a rather violent past in deep geological times, and used to have gigantic mountain ranges, similar to those in central Asia today, running across it.

It has long been recognised that the western two-thirds of the Australian continent formed much earlier than the eastern one-third, which is younger than 540 Ma. This older part of the continent, commonly with basement rocks older than 1800 Ma, hosts the vast majority of Australia’s mineral wealth. It has been assumed to have been in its present-day shape since at least 1000 Ma, with relatively modest mountain ranges popping out here and there due to minor internal jiggling.

However, a recent reanalysis of geological and palaeomagnetic data from Australia has revealed a major mountain-building event within the older part of Australia during the period 650–550 Ma, leading to the formation of a major east–west divide cutting...

The full text of this article can be purchased from Informit.