Diamond 'eruption' discovery can help find underground deposits of gems

Understanding volcanic activity offers insight into locating diamonds

The discovery, published in the journal Nature, offers new insight into locating potential diamond deposits. Reuters

One of the mysteries behind the formation of diamonds has been solved, scientists said on Tuesday, opening up the possibility that the finding can help to locate deposits deep underground.

Scientists, led by an associate professor from the University of Southampton, said they now know why diamonds “erupt” – geologically speaking – on the Earth’s surface.

They discovered that the break-up of tectonic plates is the driving force for the generation and eruption of diamond-rich magmas from deep inside the Earth.

The discovery, published in the journal Nature, offers insight into locating diamond deposits.

Until now, scientists have not understood how diamonds reached the Earth’s surface.

Lead author Dr Tom Gernon, associate professor of Earth science at the University of Southampton, said: “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.”

The research examined the effects of global tectonic forces on these volcanic eruptions spanning the last billion years.

The team, which included researchers from the universities of Birmingham, Leeds, Potsdam, Portland State, Macquarie, Florence, and Queen’s in Ontario, examined the link between continental break-up and kimberlites, the rock formations that host diamonds.

The results showed that eruptions of most kimberlite volcanoes occurred 20 to 30 million years after the tectonic break-up of Earth’s super continents.

“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,” said Dr Thea Hincks, senior research fellow at Southampton.

They then found that the Earth’s mantle: the convecting layer between the crust and core – was disrupted by rifting (or stretching) of the crust, even thousands of kilometres away.

Dr Stephen Jones, associate professor in Earth systems at Birmingham, and study co-author said: “We found that a domino effect can explain how continental break-up leads to formation of kimberlite magma.

“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 said that this process led to the conditions needed for the creation of diamond-producing kimberlites.

“Remarkably, this process brings together the necessary ingredients in the right amounts to trigger just enough melting to generate kimberlites,” he said.

The scientists said that this understanding of this kimberlite migration helps them understand the locations and timings of past volcanic eruptions and therefore the insight into locating potential diamond deposits.