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Mystery of highest Aussie mountain solved

According to the University of Sydney (UoS), the majority of the world’s mountain belts resulted from either volcanism or the collision of two continents (as was the case with the Himalayas). However, it was said that Australia’s Eastern Highlands mountain range were the exception, the mechanisms behind their formation a mystery.

The Eastern Highlands extend from northeastern Queensland to western Victoria and include the country’s highest mountain, Mount Kosciuszko in New South Wales, and the Australian Alps in the nation’s southeast.

A research team comprising geologists from UoS and the California Institute of Technology set out to investigate the cause of the uplift that created Mount Kosciuszko and the Australian Alps through the use of high performance computing code.

The team was led by Professor Dietmar Müller from UoS’s School of Geosciences. Müller said the answer lay in the mountains’ unusually strong gravity field.

“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,” he explained.

Two-phase uplift

The team’s research revealed that the mantle under Australia’s east coast has been uplifted twice – once during the Early Cretaceous period, when Australia was part of the ancient “supercontinent” Gondwanaland, and then a second time about 50 million years later.

During the Early Cretaceous period, it was said the Earth’s mantle had been “continuously stirred” through a process called subduction whereby tectonic plate sections would sink into the mantle beneath another plate.

Eastern Australia had been drifting over a “subducted plate graveyard” until subduction came to a halt around 100 million years ago. This caused the entire region to be lifted upwards, creating the Eastern Highlands. Approximately 50 million years later, Australia’s accelerated separation from Antarctica moved the region towards a mantle “upswelling” called the South Pacific Superswell, resulting in the second upwards push.

Müller said geological features from rivers in the Snowy Mountains supported the research team’s two-phase uplift computer model.

“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,” he said.

The research was recently published in Earth and Planetary Sciences.

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