Sep 24, 2023 - Science

Supercontinent breakup pushed pink diamonds to Earth's surface

pink diamonds

Pink diamonds found in the Argyle mine. Credit: Murray Rayner

The breakup of a supercontinent 1.3 billion years ago may have moved rare pink diamonds from the depths of Earth to the surface, researchers report.

Why it matters: The key role of continent movements in producing pink diamonds could point to other caches of the valuable gems.

  • More than 90% of the pink diamonds found on Earth came from the Argyle mine in western Australia.
  • But they are still "incredibly rare" — about one in 500 diamonds at the mine is pink, says Hugo Olierook, a geologist at Curtin University in Perth, Australia. The mine closed in 2020.

How it works: Scientists knew that diamonds form from carbon under intense pressure deep in the Earth.

  • They also knew that colliding tectonic plates can twist, bend and rotate the crystal lattices, turning them pink. (If they're twisted even more, they become red; even more and they turn brown.) Argyle's pink diamonds were formed more than 1.8 billion years ago when plates collided in what is now western Australia.
  • A volcano eruption brought them to surface, but scientists didn't know what triggered it and exactly when.
  • Unlike other diamonds typically found in old rock deposits in the middle of continents, the pink diamonds at Argyle are in younger rocks.

What they found: Analyzing minerals from rocks in the mine, Olierook and his colleagues found they arrived at the surface about 1.3 billion years ago — 100 million years before scientists previously thought, they report in the journal Nature Communications.

  • At that time, the supercontinent Nuna was splitting.
  • At Argyle, the land didn't break apart but stretched and thinned where the plates had collided hundreds of millions of years earlier.
  • The researchers propose that thinning created gaps in the crust through which magma could have then carried the diamonds to the surface.

Yes, but: There are open questions about the details of how the diamonds formed, and Olierook says the estimate of Argyle's age could be refined.

  • "Just because it's the exact same age as a supercontinent breakup doesn't necessarily mean it's the breakup that caused the diamond eruption," he cautions.
  • "It's a very good theory. It seems to make sense. But unless you've got a time machine and go back in time to actually witness it happening there, then it's difficult to know."
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