The landscape of eastern Australia is full of hundreds of extinct volcanoes. They created an environment in which Native Americans have been bound for tens of thousands of years, and the rich soils on which modern-day Australia has grown in the last few hundred years.
But until recently, these volcanoes were a geological mystery. There are two common volcanoes: at the edges of tectonic plates, or on top of blobs of hot material called “mantle plugs,” that rise from the depths of the planet. For most eastern Australian volcanoes, however, none of these definitions fit the bill.
We have now solved the puzzle. By studying the history of the eruptions and the chemical shape of the rocks that spat them out, we discovered a previously unknown geological device that connects volcanoes from Far North Queensland to southern Tasmania.
Australia’s volcanic eruption
You might be surprised that hundreds of volcanoes have erupted all over eastern Australia over the last 100 million years. This volcanism also spread offshore to New Zealand and the underground continent of New Zealand.
Most of the world’s volcanoes form when a process known as “extraction” pushes parts of the seabed down into the Earth’s crust, where it melts and melts. volcanism formed at the surface. The best known example of this type of volcanism is the Ring of Fire around the Minch.
Alternatively, chains of volcanic islands can be built up of hot material rising from the Earth’s deep interior – known as “mantle plumes” – in a process created by the likes of Hawaii, Iceland and Galapagos Islands. These so-called “hotspot chains” monitor the movement of tectonic plates as new islands overlap a paper reed plug.
However, most volcanoes in our backyard are not associated with mantle plugs and are not near plate boundaries. So why are they here?
Exploring the volcanic artery of Australia
Our study, published today in Science Advances, shows how often volcanic eruptions in eastern Australia and Zealand are dependent on seabed activity about 3,000 kilometers beyond. the east.
Why is this happening? It is related to the amount of water and carbon dioxide trapped in the seabed, which is recycled down into the mantle.
Over many millions of years, a reservoir of these volatile ingredients has built up in the mantle, more than 410 kilometers below the surface. This reservoir remains dormant under the Australian plate, until tectonic forces create movement forces.
As slabs of seabed are dumped at the Tonga-Kermadec Trench, which runs from New Zealand all the way to Samoa, the vibrations reach all the way to the reservoir beneath eastern Australia and Zealand. As a result, water and carbon dioxide erupt from the reservoir and rise up to volcanic eruptions at the surface.
We found our first piece of evidence for this driving process in the deep history of volcanic eruptions in the region. There were two gradual increases in volcanism, one between 60 million years ago and 21 million years ago, and the other from 10 million years ago to 2 million years ago. These times were separated by short-term (in geological terms) in explosion frequency.
Both programs were accomplished by a major reorganization of the Earth’s tectonic plates, in which the plates rapidly change speed and direction. These changes resulted in the removal of a large chunk of the Pacific floor, which led to volcanic activity when water and carbon dioxide were shaken from their healthy reservoir.
Fingerprints of Australia’s secret volcanoes
The removal process is not unique to the east coast of Australia. What sets the eastern Australia-Zealand region apart is that the seabed that is pushed beneath the continent from the western Pacific Ocean is full of substances containing water and carbon dioxide.
Not only that, but these substances appear to accumulate at shallow depths in the mantle over a long period of time, rather than sinking deeper into the Earth’s interior. This creates a deep zone in the mantle just below the east coast of Australia that is full of volatile substances.
We studied the chemical composition of the rocks that caused these ancient explosions throughout the region and found most common chemical fingerprints. These fingerprints told us that the explosions across eastern Australia and New Zealand came from a common reservoir, which may have been formed from the removal of the old seabed. This was the last piece of the puzzle that helped us connect random volcanoes over 100 million years of history.
New ‘eyes’ for study abroad and at home
Combining scenes of volcanic history, tectonic plate movements and geochemistry could help us unravel other explosive mysteries of our natural world. We hope to further test our model in other enigmatic regions where volcanoes appear in the middle of tectonic plates, such as the western United States, eastern China, and around Bermuda.
In the meantime, we hope your findings give you a new way to explore the beautiful volcanic hills and other features of eastern Australia. If you’re driving around the country in the summer, here are our top five volcanic events for your travel enjoyment:
The mystery of Australian volcanoes revealed in new study
Presented by The Conversation
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Citation: There are hundreds of enigmatic volcanoes in Eastern Australia. New research shows how they created (2020, Dec 17) on 17 Dec 2020 retrieved from https://phys.org/news/2020-12-eastern-australia-hundreds-enigmatic-volcanoes.html
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