The breakup of tectonic plates is the main driving force behind the generation and eruption of diamond-rich magmas from deep inside the Earth, a new study has found.
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. 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. But how and why they got to Earth’s surface has, until now, remained a mystery.
The new research, led by the University of Southampton alongside experts from the University of Birmingham examined the effects of global tectonic forces on these volcanic eruptions spanning the last billion years. The findings are published today (26 July 2023) in the journal Nature.
Dr Stephen Jones, Associate Professor in Earth Systems at the University of Birmingham, and study co-author said:
“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.”
30 million year wait
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 to 30 million years after the tectonic breakup of Earth’s 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
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 kilometres beneath the Earth’s surface.”
The new 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.