Geologists show how NZ and Australia broke apart

Geologists have created a mathematical model that calculates how Australia and New Zealand broke apart 100 million years ago - and say a similar process may be under way in South America.

Australian geoscientists Associate Professor Patrice Rey and Professor Deitmar Muller from Sydney University said that their paper, published this week in the journal Nature Geosciences, was the first to show how the supercontinent Gondwana broke up.

Between 105 million and 90 million years ago, Australia and New Zealand were joined with Antarctica, but the Pacific tectonic plate, which is denser and thinner than continental crust, dived under the supercontinent's east coast at the rate of 7cm to 8cm a year - about the same rate it now sinks beneath South America.

As the plates slowed, contact between the plates (the Pacific and Gondwanan) got smaller and the mountain belt along East Gondwana began to collapse, spreading under its own weight.

At the same time, the mantle - the partly molten rock under the Earth's crust - became more buoyant, pushing on the crust above, causing it to fracture.

These cracks were the first wedges driving Australia and New Zealand apart.

According to Professor Rey, a similar situation is being played out under South America, where the Pacific plate's descent has slowed from 25cm a year to about 7cm over the past 20 million years.

"If the velocity of the Pacific plate and the South American plate continue to decrease, then the [Andes] will start to collapse and parts of South America will move away from the mainland."

- NZPA