Australasian Science: Australia's authority on science since 1938

The Creation of Kosciusko

Geologists have solved the mystery of how Australia’s highest mountain – Mount Kosciusko – and the Alps surrounding it were born.

Most of the world’s mountain belts are the result of two continents colliding or volcanism, but the Eastern Highlands stretching from north-eastern Queensland to western Victoria are an exception. Until now no one knew how they formed.

Prof Dietmar Müller of the University of Sydney used computer models to investigate the cause of the uplift that created the mountain range, and found the answer in the unusually strong gravity field of the mountains.

“The gravity field led us to suspect the region might be pushed up from below, so we started looking at the underlying mantle: the layer of rock between the Earth’s core and its crust,” Müller said.

It turns out that the mantle under Australia’s east coast has been uplifted twice. The first time occurred during the Early Cretaceous, when Australia was part of Gondwana and geological processes were pushing the Earth’s tectonic plates under one another in a process known as subduction.

“Eastern Australia was drifting over a subducted plate graveyard, giving it a sinking feeling,” said co-author Dr Kara Matthew. “But around 100 million years ago subduction came to a halt, resulting in the entire region being uplifted, forming the Eastern Highlands.”

The next 50 million years was a time of relative inactivity. “Then, about 50 million years ago, Australia’s separation from Antarctica accelerated and it started moving north–north-east, gradually taking it closer to a vast mantle upwelling called the South Pacific Superswell,” said co-worker Dr Nicolas Flament. “This provided a second upward push to the Eastern Highlands as they gradually rode over the edge of the superswell.”

Müller said the two-phase uplift suggested by supercomputer models is supported by geological features from rivers in the Snowy Mountains, where river incision occurred in two distinct phases. “The model we built explains why the iconic Australian Alps exist, and is also a new mechanism for figuring out how some other mountainous regions elsewhere in the world were formed.”

The team’s findings have been published in Earth and Planetary Sciences (www.tinyurl.com/heelojx).