Study sheds new light on the origins of East Australian volcanoes

Volcanoes follow a complex geologic pattern that is defined by the geologic foundations on which they are built.

The origin of the Trans-Tasman volcanoes remain a mystery however new research by Australian and New Zealand geologists has now found a link between these volcanoes and the deep burial mechanism of Earth’s tectonic plates.

The research, led by Monash University Bachelor of Science alumnus Dr Ben Mather (now at the University of Sydney), and involving PhD candidate Saskia Ruttor and Associate Professor Oliver Nebel from the Monash School of Earth, Atmosphere and Environment is published today in Science Advances.

Eastern Australia and the seafloor of the Tasman Sea between Australia and New Zealand are covered by a large number of small volcanoes.

On-shore volcanoes in Queensland, New South Wales and offshore submarine edifices on the ancient Zealandia microcontinent represent a massive volcanic field with eruption centres of seemingly random distribution.

“Volcanoes, however, do not occur randomly and follow a complex geologic pattern that is defined by the geologic foundations on which they are built,” said Associate Professor Nebel.

The three main groups of volcanoes are massive Ocean Islands like Hawaii or Samoa, explosive Ring-of-Fire volcanoes such as those in greater Indonesia, and deep-sea, oceanic mountain-chain volcanoes along tectonic plate suture zones.

The Trans-Tasman volcanoes do not belong to these categories, and their origin remains a mystery.

“The new study has found a common source for all volcanoes using computational reconstructions of past plate movements and the chemical fingerprint of the volcanic roots,” Associate Professor Nebel said.

Earth’s plates delve back into the mantle at so-called subduction zones, the regions where plates converge and collide.

When one plate sinks underneath the other, on its way towards the Earth’s interior, oceanic crust breaks and deforms under extreme pressure and temperature, and leaves a trail of crustal crumbs.

These crustal remnants accumulate in an area known as the Mantle Transition Zone, 400-600 km below the surface – and if returned towards the surface can melt to create new volcanoes.

“Our research shows that when the Zealandia plate was wedged into this crustally infused transition zone, parts of ancient crust was pushed upwards over the last tens of millions of years,” said Associate Professor Nebel.

“This deep-Earth domino effect is the reason for our volcanoes,” he said.

“We now know that these volcanoes form by a burst of material from deep in the Earth that rises underneath the ocean floor.

“This is very exciting, and shows that we only just start to begin to understand the complex process that are at play underneath our feet.”

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