Giant Heat Plumes Deep in Earth Revealed: The Fires That Ignite Diamond Eruptions

The majority of diamonds are created deep inside the Earth and are transported to the surface by little but mighty volcanic eruptions of a kind of rock known as "kimberlite."

Our supercomputer simulation, which was published in the journal Nature Geoscience, demonstrates that these eruptions are driven by enormous "pillars of heat" that are buried 2,900 kilometers (1,802 miles) below the surface, right above our planet's core.

Targeting mineral deposits, including those for important minerals like nickel and rare earth elements as well as diamonds, may be done by understanding Earth's interior history.

Warm blobs and kimberlite

An iconic deep, carrot-shaped "pipe" of kimberlite rock, which frequently has diamonds, is left behind by kimberlite eruptions. Around the planet, hundreds of these eruptions from the last 200 million years have been found. The majority of them were discovered in Brazil (70), South Africa (158), Angola (71) and Canada (178 eruptions).

The mantle, a substantial layer of heated, somewhat gooey rock, sits between the solid crust of Earth and its molten core. Geophysicists have studied the sluggish, long-term movement of the mantle using computers for many years.

One research from the 1980s suggested that tiny thermal plumes in the mantle, which rise upward beneath slowly moving continents and resemble feathers, may be related to kimberlite eruptions.

At a depth of 2,900 kilometers, the mantle-core barrier had previously been suggested as the possible source of these plumes in the 1970s.

Then, in 2010, geologists suggested that kimberlite eruptions may be explained by thermal plumes that were produced by the margins of two hot, deep blobs that were anchored beneath Africa and the Pacific Ocean.

Additionally, we noted that these anchored blobs are more mobile than we initially believed last year.

However, we were still unsure of the precise mechanism guiding kimberlite eruptions, which was caused by deep mantle activity.

Heat pillars

Geologists believed that mantle plumes could be what sparks kimberlite eruptions. A significant puzzler remained, though: how was heat getting from the deep Earth to the kimberlites?

We developed three-dimensional geodynamic models of the Earth's mantle using supercomputers in Canberra, Australia, in order to answer this question. Our models take into consideration how continents have moved over the last billion years, both on the surface and beneath the mantle.

We computed the heat flow from the core and found that the extremely deep Earth is connected to the surface via wide mantle upwellings, or "pillars of heat". Our simulation demonstrates that these pillars provide heat beneath kimberlites and that they account for the majority of kimberlite eruptions during the previous 200 million years.

The kimberlite eruptions in Africa, Brazil, Russia, and to a lesser extent in the United States and Canada were successfully represented by the model. Our simulations also indicate that kimberlite eruptions in East Antarctica and the Yilgarn Craton of Western Australia, which were previously unknown, may have taken place.

Mantle plumes rise more quickly and transport dense material over the mantle into the heart of the pillars, which might account for the varying chemical composition of kimberlites on various continents.

Some of the Canadian kimberlites, which may be connected to a separate geological phenomenon known as "plate subduction," are not explained by our models. The oldest kimberlites can be dated to one billion years ago, which is the limit of our ability to recreate tectonic plate motions at this time.

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