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Geologists have claimed that “the oldest collision crater in the world” – the vast Maniitsoq structure located on the west coast of Greenland – is not really like that.
And in 2012, an international team of researchers suggested that the 100 km-wide structure was formed by a giant impact about 3 billion years ago.
There is no nozzle-shaped bowl in Maniitsoq. Researchers say this is eroded because the current surface was buried 14 miles away at the time of the collision.
Instead, the team pointed to a magnetic anomaly, as well as signs of circular fissuring in the deep cortex – which they said was evidence of trauma penetration.
However, this was greeted with skepticism, with some experts claiming that the Maniitsoq structure did not meet enough criteria for its classification as a crater.
Now, researchers led by Canada have shown that the structure is indeed shaped by the same regular geological process as the surrounding area.
In fact, some of the molten rocks in the heart of the alleged crater were similar to those in the vicinity, outside of the proposed zone of influence.
The search for impact craters has continued now since the Archean period, 4-2.5 billion years ago, when continents were newly created and life on Earth was just beginning.
Evidence of intense impact activity during this time can be found in iconic craters on the moon’s surface – but their terrestrial counterparts are still elusive.
Read more
It is possible that no evidence remains and that there is evidence that eroded long ago or was buried under much smaller rocks.
Geologist Chris Yakimchuk of the University of Waterloo in Canada conducted the study which refuted the hypothesis of the effect.
“Our results categorically rule out the suggestion that much of the rock mass in the Maniitsoq region was formed by the impact of the Archeus meteorite,” the team wrote.
This “leaves the 2.23 billion year old Yarrabubba structure in Western Australia as the oldest structure confirmed for ground shocks. The craters source of ancient impact projectiles remain elusive on Earth,” they added. .
In their study, Prof. Yakimchuk and his team combined mapping of geological outcrops in the field with rock dating and chemical analysis, to get to the bottom of the formation of the Maniitsoq structure.
They found that the individual magnetic readings identified in the previous study did not persist in the wider region, as one would expect if this signature was formed by an impact event – and magnetic scans only revealed no circular impact structure.
The researchers analyzed 5,587 grains of a mineral called zircon, looking for evidence of a knockdown effect on their crystal structure.
“Zircons in rock are like little time capsules,” said Prof Yakimchuk.
Additionally, analysis of oxygen isotopes in zircon revealed no evidence that rocks of the Maniitsoq structure were ever exposed to the influx of warm seawater through forged cracks, as suggested. previously.
If the water changed the rocks in the area, they would have become rich in the light isotope of oxygen which is relatively more common in seawater than rocks.
The team’s investigation also found that some of the rocks that would have melted and repaired as a result of the high-energy impact were actually around 40 million years younger than previously thought.
Finally, the team found a piece of rock that intersected the proposed collision site that was at least 100 million years younger than it, but which was also buried, heated, and deformed.
It would not be possible, the researchers explain, for these rocks and evidence of an ancient influence to coexist together in the rock disc – the latter would not survive these changes.
The full results of the study are published in the journal Earth and Planetary Science Letters.
Source: Daily Mail
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