The long-standing puzzle of how and why diamonds erupt from Earth’s interior having spent billions of years locked up at the roots of continents has been solved by scientists, led by an Irishman.
The break-up of continents instigates a chain reaction inside the Earth, disturbing the continental roots and triggering eruption of diamonds.
This discovery by an international team led by Dr Tom Gernon, an Irish scientist at the University of Southampton, could shape the future of the industry by informing where diamonds are most likely to be found.
The findings could be used to identify possible locations and timings of past volcanic eruptions tied to this process; offering valuable insights that could enable the discovery of future diamond deposits.
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Break-up of tectonic plates is the main driving force behind generation and eruption of diamond-rich magmas from deep inside the Earth, he explained.
The plates are gigantic pieces of the Earth’s crust and uppermost mantle. They are made up of oceanic crust and continental crust. Earthquakes occur around mid-ocean ridges and the large faulted boundaries which mark the edges of the plates.
“Diamonds, which form under great pressures at depth, are hundreds of millions, or even billions, of years old. They are typically found in a type of volcanic rock known as kimberlite,” Dr Gernon said.
Kimberlites are found in the oldest, thickest, strongest parts of continents – most notably in South Africa, home to the diamond rush of the late 19th century and Botswana. But how and why they got to Earth’s surface has, until now, remained a mystery.
“Nobody knew why they were there in the first place,” said Co Louth man Dr Gernon, an associate professor of earth science at the university.
“The pattern of diamond eruptions is cyclical, mimicking the rhythm of the supercontinents, which assemble and break up in a repeated pattern over time. But previously we didn’t know what process causes diamonds to suddenly erupt, having spent millions – or billions – of years stashed away 150 kilometres beneath the Earth’s surface.”
As a pupil at Coláiste Rís in Dundalk, he won the Young Scientist and Technology Exhibition in 2000 with a project on “The Geography and Mathematics of Europe’s Urban Centres” before going on to study geology in UCD.
His team used statistical analysis, including new approaches to AI and machine learning, “to forensically examine the link between continental break-up and kimberlite volcanism”.
Their results show eruptions of most kimberlite volcanoes occurred 20 to 30 million years after the tectonic break-up of Earth’s continents. Their research was published in Nature on Wednesday.
His colleague Dr Thea Hincks said: “Using geospatial analysis, we found that kimberlite eruptions tend to gradually migrate from the continental edges to the interiors over time at rates that are consistent across the continents.”
This discovery prompted the scientists to explore what geological process could drive this pattern. They found that the Earth’s mantle – the convecting layer between the crust and core – is disrupted by rifting (or stretching) of the crust, even thousands of kilometres away.
“We found that a domino effect can explain how continental break-up leads to formation of kimberlite magma,” said Dr Stephen Jones of the University of Birmingham.
“During rifting, a small patch of the continental root is disrupted and sinks into the mantle below, triggering a chain of similar flow patterns beneath the nearby continent.”
Dr Gernon was recently awarded a major philanthropic grant to study factors contributing to global cooling over time. This work was important “to really understand what’s driving climate change”, he said.
This includes understanding better what drove major climate events, and especially cooling, in the past, he said.
“A lot of the solutions to today’s problems are encrypted in the past,” he said. “This grant will help to supercharge that work.”
