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Monash University team investigate “unusual” rocks on Tasmania’s NW coast

Research finds match with rocks from the Grand Canyon in the USA

Confirms both land masses were part of the same supercontinent more than 700 million years ago

A part of the north-west coast of Tasmania is the Grand Canyon’s long-lost cousin.

A paper recently published in the journal Geology by geologists at Monash University followed a hunch about these rocks:

Picture: Peter Farquhar/Business Insider

They’re part of a very famous bit of land, Rocky Cape National Park, where cave middens reveal evidence of Aboriginal occupation from at least 8000 years ago. It’s been officially recognised as “pinmatik” (“peen mah teek”) since 1991.

But hundreds of millions of years ago, it was part of a megacontinent known as Rodinia, and joined to what is now known as the west coast of the USA, 13,000km away.

In particular, it’s got bits of the Grand Canyon in it, and that makes it very, very interesting for earth science researchers.

Rodinia was formed when an even older supercontinent known as Columbia broke apart, but you won’t find any Rodinian fossils at Rocky Cape, because Rodinia existed one billion years ago, well before terrestrial life had formed.

It began breaking up around 700 million years ago.

Picture: Peter Farquhar/Business Insider

The discovery was made by Jack Mulder, a research fellow at Monash University in Melbourne, who thought the rocks looked similar to those in the Grand Canyon, and decided to test his theory.

The hunch turned out to be on the money. Rocks from both regions shared similar stratigraphy, depositional age, and they contain matching hafnium isotopes readings.

Mulder was able to trace where the ancient sand and mud came from by analysing the geochemical fingerprint of tiny grains of the mineral zir-con, which makes up a small proportion of the sedimentary rocks.

“When we compared the Tasmanian rocks to similar-aged rocks nearby in Australia, we found that not only did they look very different, but they also had distinct zircon fingerprints. Instead, the enigmatic Tasmanian rocks look strikingly similar to the one billion year old sedimentary rocks found near the bottom of Grand Canyon in Arizona,” he says.

“In addition to forming at the same time and in similar geological environment, the ancient sedimentary rocks in Tasmania and Grand Canyon share the same zircon fingerprint. Together, this evidence supports the interpretation that these now widely separated rock units once formed part of the same sedimentary basin.”

That dates pinmatik back as much as 1.1 billion years to the late Mesoproterozoic era.

One such professor, Alan Collins, at the University of Adelaide, Australia, told New Scientist the paper shows Tasmania “holds the key” to understanding how the planet was put together.

It could help future geologists build full plate models of ancient Earth, he said.

You can read an excerpt of the report here.

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