An international team of scientists, including Christopher Spencer from Queen’s University, have discovered that the breakup of tectonic plates is the main driving force behind the generation and eruption of diamond-rich magmas from deep inside the Earth. Their findings could shape the future of the diamond exploration industry, informing where diamonds are most likely to be found.
Diamonds, which form under great pressures at depth, are hundreds of millions, or even billions, of years old. They are typically found in kimberlite, which is found in the oldest, thickest, strongest parts of continents. But how and why they got to Earth’s surface has, until now, remained a mystery.
The new research examined the effects of global tectonic forces on these volcanic eruptions spanning the last billion years. The findings were published July 26, 2023, in the journal Nature.
Researchers collaborated from Queen’s University, the University of Birmingham, the University of Potsdam, Portland State University, Macquarie University, the University of Leeds, and the University of Florence.
Dr. Tom Gernon, associate professor of earth science and principal research fellow at the University of Southampton, and lead author of the study, 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 km beneath the Earth’s surface.”
To address this question, the team used statistical analysis, including machine learning, to forensically examine the link between continental breakup and kimberlite volcanism. The results showed the eruptions of most kimberlite volcanoes occurred 20 million to 30 million years after the tectonic breakup of Earth’s continents.
Dr. Christopher Spencer, associate professor at Queen’s University, and study co-author 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.”
Geological processes
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 breakup 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,” said Spencer. “The confluence of numerous lines of evidence from paleogeography, geodynamic simulations, and isotope geochemistry of kimberlites require a dramatic rethinking of the previous paradigm and the newly presented model satisfies all the evidence.”
The team’s research could be used to identify the possible locations and timings of past volcanic eruptions tied to this process, offering valuable insights that could enable the discovery of diamond deposits in the future.
Gernon said the study also sheds light on how processes deep within the Earth control those at the surface. “Breakup not only reorganises the mantle but may also profoundly impact Earth’s surface environment and climate, so diamonds might be just a part of the story.”
Contact Christopher Spencer by email: [email protected].
