The presence of pink diamonds on Earth may be attributed to the fragmentation of the planet’s initial supercontinent. The primary source of 90% of the world’s pink diamonds, the Argyle formation located in Western Australia, stands out as an unusual site for diamond mining. Unlike most diamond mines that are typically found in the heart of continents, the Argyle’s unique geological setting has intrigued researchers.
Recent studies now suggest that both the distinctive color and geological characteristics of the Argyle pink diamonds may share a common origin, dating back approximately 1.3 billion years ago during the era of plate tectonics. Other researchers have previously indicated that large-scale continental movements play a pivotal role in bringing diamonds of various colors to the Earth’s surface.
Hugo Olierook, a research fellow at Curtin University in Australia and the lead author of a new study on the origin of pink diamonds published in the journal Nature on September 19th, explains, “The breakup of these continents is fundamental for bringing these diamonds up from these deep depths.”
Pink diamonds differ from their blue or yellow counterparts, which obtain their color from impurities such as nitrogen and boron. In contrast, pink diamonds owe their color exclusively to structural deformations in their crystalline structure. The Argyle formation also hosts a significant number of brown diamonds, which exhibit even greater structural deformations.
Olierook describes the difference, stating, “Pinks are, say, a small push, if you like. You push a little bit too hard and they turn brown.”
The Argyle diamond mine ceased operations in 2020. Previous research from the 1980s had estimated the age of the rocks in the area at about 1.2 billion years, although even the scientists who conducted this earlier work were unsure about this figure due to technological limitations. Olierook and his colleagues revisited this estimation using modern laser ablation technology, allowing them to precisely date the individual crystals in the rock.
Their new findings revealed that the Argyle, which contains pink diamonds, is actually 100 million years older than previously thought, dating back to 1.3 billion years ago. This timing coincides with the initial stages of the breakup of the supercontinent Nuna.
According to Olierook, this discovery paints a new picture of how Argyle’s pink diamonds came into existence. Around 1.8 billion years ago, two pieces of continental crust collided during the formation of Nuna. The Argyle formation was situated at the point of this collision. It is likely that this crustal collision is what caused the diamonds to deform and turn pink.
The subsequent breakup of Nuna, 500 million years later, brought these diamonds closer to the Earth’s surface. Although the continent did not separate directly beneath the Argyle, the stretching during this period likely weakened the “old wound” from the earlier continental collision where the formation was located. This weakening facilitated the eruption of deep rock, carrying with it the rare pink diamonds, occurring over a span of days to weeks.
Olierook suggests, “I think we’re seeing how in general, the mantle is destabilized when supercontinents break up. That rifting process seems to not just work the edges but also seems to work in the middle of continents, and that’s perhaps what is allowing diamonds to come up in the middle of them” in most cases.
Understanding the journey of diamonds from the Earth’s depths to the surface provides valuable insights into how carbon cycles in and out of the planet’s interior, given that diamonds consist primarily of carbon. While the Argyle stands as a unique location, Olierook believes there is a possibility of finding other pink diamond deposits elsewhere on Earth. However, the challenge lies in the fact that if pink diamonds form on the edges of continents, they are likely buried under layers of eroded rock and sediment.
“I do think we will find another Argyle, another pink diamond treasure trove,” Olierook concludes, “but it’s going to take a lot of luck.”