Source: abc.net

Geologists say they have discovered a large meteorite crater in outback Western Australia, which could be up to five times bigger than the famous Wolfe Creek Crater in the state’s remote north.

The impact crater was located near the historic Goldfields mining town of Ora Banda, north-west of Kalgoorlie-Boulder, while drilling for gold.

It is not visible from the surface but electromagnetic surveys, which map the rocks below, suggest the crater has a diameter of around 5 kilometres.

Perth-based geologist and geophysicist, Jayson Meyers, said the asteroid that made the crater would have been at least 100 metres wide.

“Based on its position and levels of erosion and some of the soil that is filling the sides, we estimate it could be around 100 million years old,” Dr Meyers told the ABC.

“That’s a guess — and some colleagues at Curtin University are going to now use age dating to give us some more precise dates.”

‘Shatter cones’ a tell-tale sign

The crater is located about 10 kilometres south-east of Ora Banda, on land owned by Australia’s third-biggest gold miner, Evolution Mining.

Dr Meyers, who has more than 30 years’ experience in the field and is an adjunct Associate Professor in exploration geophysics at the WA School of Mines, was brought in as a geological consultant.

The California native said close inspection of drilling samples from the site have convinced him.

He said the rock samples had “tell-tale signs” of a meteorite strike, including what is known as “shatter cones”, which under a microscope look like shattered glass and form in a certain direction.

“In geology, you tell someone you found a meteorite crater and they immediately roll their eyes and are very sceptical because they’re so rare,” he said.

“But when you see shatter cones you know because they only form in nuclear blasts or meteorite impacts.

“We were convinced and pretty excited from a technical standpoint — it doesn’t have a lot to do with the gold, it’s actually smashed the gold around a bit – but we can say hand over heart that an asteroid hit this spot.”

He said the Ora Banda crater looks to be much larger than the Wolfe Creek Crater in the WA Kimberley, made famous by a 2005 horror film.

Expert concurs with ‘exciting’ find

Aaron Cavosie, from Curtin University’s Space Science and Technology Centre, was part of the team which, earlier this year, discovered the Earth’s oldest asteroid strike near Meekatharra in WA’s mid west.

The research used isotopic analysis to calculate the precise age of the Yarrabubba crater for the first time, putting it at 2.229 billion years old — making it 200 million years older than the next oldest impact.

Dr Cavosie said the process to verify and date a new crater is strict, but he concurred with Dr Meyers’ initial assessment that the Ora Banda site is likely a meteorite crater.

“From my point of view, it’s pretty exciting … there’s a lot of indicators there that look pretty good,” he said.

“We have to use specialised microscopes that peer down at things smaller than a human hair and look for that tell-tale sign of unique damage that’s only caused by high-pressure shock waves.

“When we see it, there’s a little bit of an ‘aha’ moment because the only the thing that can do that in nature is an asteroid strike.”

Dr Cavosie said the advent of Google Earth meant there is now an “army of experts” that search the globe for circular features that may be meteorite impact craters.

“And boy, nature makes a lot of round things,” he said.

“So, if you get on Google Earth you’re going to have a party with all the circular things you find.”

Coolgardie crater on geologist’s radar

While still buzzing about the Ora Banda find, Dr Meyers is also trying to prove the 2017 discovery of a meteorite crater near the goldrush town of Coolgardie.

He named that find the “Meyers crater” and estimated it had a diameter of 800 metres, stretching up to 200 metres below the surface at its deepest point.

“That’s a flat area which has been filled in and when you drill into it you have 15 metres of mud and below that, it’s nothing but wood fragments for the next 150 metres,” Dr Meyers said.

“Those wood fragments will be looked at by palaeontologists who can tell by the plant types to give it an age.

“I suspect that one could be 800,000 years old at its youngest, which geologically is just a drop in the bucket.”

Dr Meyers said modern technology was making the discovery of hidden meteorite craters more common and he has several other suspected sites in WA.

He said they can only be confirmed by drilling, or the “wand of truth” as he called it.

“I can say ‘watch this space’ as we have found a few others, but we just haven’t drilled them yet,” Dr Meyers said.

Source: abc.net