Two researchers from Queensland University of Technology (QUT) used a simple laptop and a piece of rock from the “waste pile” of a diamond mine to uncover a longstanding geological mystery surrounding diamond formation at the deep roots of Earth’s ancient resources. continents. Lead author, QUT Ph.D. student Carl Walsh, along with QUT Professor Baltz Cumber and Emma Tomlinson of Trinity College, Ireland, recently published their findings in the prestigious journal. Nature.

Mr Walsh said his research for his Masters included computer simulations of rocks from the African continent that were extracted from the bottom of the lithosphere, the outer part of the Earth, about 30 to 250 km from the surface. Mr Walsh said the dominant part of the continent is the part you never see.

“If you think of an iceberg – the visible part – if the iceberg were floating on the surface of the ocean, it would capsize like a boat. It’s like the tip of the iceberg,” said Mr. Walsh.

“In fact, we had a known composition of source rock that represented the Earth’s mantle during the early stages of Earth’s history before all continents formed,” Walsh said. “We took the initial composition and modeled what would happen to it and what would be left if it melted gradually. And it is this material that forms the main part of the roots of ancient continents that still exist today.”

Professor Camber, from QUT’s School of Earth and Atmospheric Sciences’ School of Life Sciences, said the aim of the study is to use a computer model to see how these deep roots form.

“The model essentially predicts what minerals and melts will be found when you change the temperature of the mantle. So it’s a predictive tool that can be compared to the composition of real minerals and rocks,” he said.

The boulder used for advanced computer modeling was mined between 1871 and 1914 and ended up in the “waste pile” of the legendary Kimberley diamond mine, a combination of open pit and underground mine best known as the Big Hole. – North Cape in South Africa, in Kimberley.

The boulder they modeled, garnet harzburgite, was brought to the surface in a kimberlite tube. The stone was obtained by Professor Cumber, who specializes in petrology, the branch of geology that studies rocks and the conditions in which they were formed.

He carefully hewed the stone to a size that he could successfully deliver home.

“It contains a group of minerals that were trapped as they ascended as they cut through the bottom of the entire continent in a supersonic volcanic eruption, the like of which we have never seen,” Professor Cumber said. “The minerals in this rock sample were so badly damaged that they still scream today, they were completely broken.”

“It’s very exciting to see it preserved, it’s incredibly old at 3.3 billion years. Probably the oldest stone most people have ever held,” Professor Cumber said.

Mr Walsh said the research has solved the diamond problem and the temperatures at which they form, given that diamonds turn into graphite when heated too much.

“But looking at rocks containing diamonds, they must have been heated to very high temperatures,” Walsh said. “And why are the rocks exposed to the highest temperatures that resulted in the discovery of diamond?”

Their research challenges the current explanation for the two-stage shallow “melting and stacking.”

“It was previously thought that many of the ancient deep roots of the continents contained diamonds, and that these diamonds were destroyed over time as the continent’s floor was continually occupied and eroded by volatile-rich melts and liquids,” Walsh said. “Our work shows that diamonds may not actually be rare today, and they have always been rare. And that’s because for the first time we’ve been able to find what’s missing in a diamond’s cradle and look for it on the surface.”

Professor Cumber said the distribution of heat and temperature in the mantle on the modern Earth is uneven.

“We have regions with a relatively uniform mantle temperature and regions where the mantle is much warmer. These are known as mantle plumes. And this has an expression in Hawaii and Iceland,” said Professor Cumber. “What we’re studying is the effect of ancient plumes — much hotter plumes than we have now, that would hit the floor of a growing continent.”

After conducting the research, Mr. Walsh traveled to Canberra to reproduce similar stones in a laboratory at the Australian National University’s School of Earth Sciences.