Giant ‘Pillars of Heat’ Transporting Diamonds from Deep Inside Earth Discovered by Supercomputers

Most diamonds are formed deep within the earth and come close to the surface in small but powerful volcanic eruptions of a type of rock called kimberlite.

Supercomputer Modeling, published in Natural Earth Sciencesshows that these eruptions are fueled by giant “heat plumes” that extend 2,900 kilometers underground, just above our planet’s core.

Understanding the Earth’s inner history can be used to target reserves of minerals – not just diamonds, but also important minerals such as nickel and rare earth elements.

Kimberlite and hot spots

Kimberlite eruptions leave behind a distinctive deep, carrot-shaped “tube” of kimberlite rock, which often contains diamonds. Hundreds of such explosions that occurred within the past 200 million years have been discovered all over the world. Most of them were found in Canada (178 eruptions), South Africa (158), Angola (71) and Brazil (70).

Between Earth’s solid crust and molten core is the mantle, a thick layer of hot, slightly viscous rock. For decades, geophysicists have used computers to study how the mantle flows slowly over long periods of time.

in the eighties, One study showed that kimberlite eruptions may be related to small thermoplastic plumes in the mantle—upward, feather-like jets of hot mantle rising due to their higher buoyancy—under the slowly moving continents.

was her previously arguedin the 1970s, that these plumes may originate from the boundary between the mantle and the core, at a depth of 2,900 km.

Then, in 2010, geologists suggested The kimberlite eruptions can be explained by thermal plumes arising from the edges of two deep, hot points anchoring under Africa and the Pacific Ocean.

And last year, we reported that these fixed points are more mobile than we thought.

However, we still don’t know exactly how activity deep in the mantle was driving the kimberlite eruptions.

heat poles

Geologists have hypothesized that mantle plumes could be responsible for igniting kimberlite eruptions. However, one big question still remains: How was heat transferred from deep within the Earth to the kimberlites?

To address this question, we used supercomputers in Canberra, Australia to create 3D geodynamic models of the Earth’s mantle. Our models represent the movement of the continents at the surface and in the mantle over the past billion years.

We calculated upward motions of heat from the core and discovered that broad mantle layers, or “heat plumes,” connect very deep Earth to the surface. Our modeling shows that these plumes provide the heat beneath the kimberlite, and explain most of the kimberlite eruptions over the past 200 million years.

The model successfully captures kimberlite eruptions in Africa, Brazil, Russia, and partly in the United States and Canada. Our models also predict previously undetected kimberlite volcanic eruptions in East Antarctica and Yilgarn Craton in Western Australia.

Earth’s “heat poles” can be used in a global convection model to predict kimberlite eruptions. Credit: Ömer F. Bodur

Towards the center of the plumes, mantle plumes rise faster and carry dense material through the mantle, which may explain chemical differences between kimberlites in different continents.

Our models do not account for some of the kimberlites in Canada, which may be related to a different geological process called ‘plate subduction’. We have so far projected kimberlites back to 1 billion years ago, which is the current limit of Reconstruction of tectonic plate motions.

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