The fast-moving Indo-Australian plate.

Credit: University of Melbourne School of Earth Sciences

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SYDNEY: The giant continental plate that carries Australia is travelling faster than the underlying hot rocks of the Earth's mantle, creating pressures that may eventually split the continent, an Australian conference has heard.

Australia sits on a large crustal 'plate' that extends from Indonesia, New Zealand and part way to Antarctica, all the way to India and the Himalayan ranges. It's moving relatively fast for a tectonic plate, skipping along at the geologically rapid rate of about 7.3 cm per year in a north-easterly direction.

Beneath the plate, the moving, partly melted rock layer known as the asthenosphere, part of the Earth's upper mantle, is thought to partly drive this plate motion. The Indo-Australian plate is also pulled by gravity as it sinks or subducts along the Pacific 'rim of fire'.

Rising Nullarbor suggests plate deformation

But geological features around Australia hint at a more complex story, geologist Mike Sandiford, from the University of Melbourne told the Australian Earth Sciences Convention last week.

These features include the tilting of parts of the South Australian coast, the lack of large carbonate deposits in the north of Australia and the shape of volcanic provinces in southern Victoria, Sandiford says.

“South Australian shorelines show west Nullarbor has risen up by up to 300 metres. This can’t be explained alone by changes in sea level and hints that some deformation is happening that is uplifting the south-western part of Australia,” he says.

Volcanic regions and tilted lakes

Ancient lake beds in South Australia also show evidence of this titling, he says. “Lake Eyre is a recent (less than 10 million year old) geological feature and is not a flat-bottomed lake, being deeper in the south - in fact all South Australian lakes are tilted to the south,” he says. “It may signal something is happening to pull that lake southwards.”

Other evidence comes from geologically young volcanic rocks in Victoria, some of which may have erupted as recently as 4000 years ago.