How Do Diamonds Make Their Journey from Earth's Core?


| LAST UPDATE 08/07/2023

By Stanley Wickens
diamond formation earth volcano
lalesh aldarwish via Pexels

"Diamonds are forever," goes the famous saying. But do you know how these shiny gems make their way from deep inside the earth to your jewelry box? Well, it's quite a journey! And the latest research, published in Nature, reveals some exciting new insights about this process.

Diamonds form under extreme heat and pressure, conditions only found deep within our planet. So, how do they get to the surface? The answer is kimberlites: special types of molten rocks that carry diamonds up from the earth's depths. This happens as part of the supercontinent cycle: a pattern where large landmasses form and break apart over time. It's a process that's shaped the earth over billions of years. One theory suggests that when the earth's crust stretches or tectonic plates (large slabs of rock that cover the earth) split up, it creates "wounds". Kimberlite magma uses these wounds to reach the surface. Another theory involves mantle plumes. These are massive movements of molten rock from deep within the earth.

volcano magma diamond rock
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But there's a problem. Many kimberlites don't have the chemical traits we'd expect if they came from mantle plumes. Also, the formation of kimberlites involves very little melting of mantle rock, often less than 1%. So, we needed another explanation. Statistical analysis and machine learning were used to study the link between continental breakup and kimberlite volcanism. It turns out most kimberlite eruptions happened 20 to 30 million years after continents broke apart. Not only that, but these eruptions gradually move from the edges of continents towards the center over time. When continents break up, a small part of the continental root (thick rock areas under continents) sinks into the mantle. This creates a flow of colder material sinking and hot mantle rising, causing edge-driven convection, which then triggers similar flow patterns beneath the nearby continent. This removes a lot of rock from the base of the continental plate.

This process brings together the right ingredients to trigger just enough melting to create gas-rich kimberlites. Once formed, the buoyancy provided by carbon dioxide and water helps the magma rise rapidly to the surface, carrying diamonds with it. This information could help us predict where and when past volcanic eruptions occurred, potentially leading to new diamond deposits. So, while diamonds may or may not be forever, our research shows that new ones have been constantly forming throughout earth's history. Isn't that fascinating?

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