Scientists discover the substance that brings diamonds 93 miles up to Earth's surface

Diamonds hitch a ride to the surface inside a rare magma called kimberlite, but only if that magma stays buoyant. New modeling shows that a minimum of 8.2 percent carbon dioxide helps make that possible.

The analysis centers on the Jericho kimberlite in northern Canada and explains how diamonds can ascend from more than 93 miles deep.

A team of scientists tested how water and carbon dioxide change the magma’s lift on its sprint to daylight.

Why diamonds need speed

Diamonds survive the trip only if ascent is fast enough to keep them from turning into graphite, the soft carbon form stable at shallow conditions. Quick travel preserves their structure until eruption suddenly cools them.

The work was led by Ana Anzulović, a doctoral research fellow at the University of Oslo’s Centre for Planetary Habitability. Her research focuses on atomistic models that explain how volatile rich magmas move and evolve.

Kimberlite, magma, and diamonds

In the simulations, dissolved volatile, an easily vaporized chemical such as water or carbon dioxide, controls whether the melt stays lighter than surrounding rock.

Modeling results show that at least 8.2 percent carbon dioxide is needed to cross the crust mantle boundary.

The boundary is where buoyant melts can stall without enough gas pressure to push upward. With the right mix, the melt keeps rising into the crust without losing cargo.

“The most important takeaway from this study is that we managed to constrain the amount of CO2 that you need in the Jericho kimberlite to successfully ascend through the Slave craton,” said Anzulović.

Our most volatile-rich composition can carry up to 44% of mantle peridotite, for example, to the surface, which is really an impressive number for such a low viscosity melt.”

The team noted that it was surprising to see how a model built on such a small system could still show that, without carbon, the melt would become denser than the surrounding craton and fail to erupt.

The case of the Jericho pipe

Jericho is located in the northern Slave craton, an ancient, stable continental core that preserves deep mantle history. Its kimberlite erupted into an old crust that acts like a gatekeeper for rising melts.

As kimberlite moves, it rips up fragments called xenolith, a foreign rock piece carried by magma, and individual crystals called xenocrysts. Those pieces record chemistry from depth and help map the magma’s path.

The team explained that the goal was to build a chemical model of a kimberlite and adjust the amounts of carbon dioxide and water to see how the melt would behave.

They described the approach as a way to sample the magma at different depths by tracking how it would change with shifting pressure and temperature.

The team used atom by atom calculations to track density changes as pressure fell. That approach revealed which mixtures stayed buoyant and which compositions stalled.

Water and carbon share the job

A paper showed that gas coming out of solution can power rapid kimberlite ascent. The new modeling adds that water and carbon dioxide help in different ways along the route.

Water raises diffusivity, the rate atoms move through a melt, which tends to lower viscosity and keep flow lively. Carbon dioxide strengthens the melt structure at depth, then bubbles out near the surface to drive the final push.

All the modeled melts were lighter than the mantle beneath the lower crust. The 8.2 percent threshold matters most at the crustal gate where buoyancy margins get thin.

The crust mantle boundary is the Moho, a seismic line marking a sharp change in rock properties. Crossing it cleanly is essential for preserving diamonds and their mineral companions.

What rises for the ride

Kimberlite can hoist large loads of mantle peridotite, a dense, olivine rich rock from Earth’s upper mantle, to the surface. That cargo samples conditions where diamonds grow and where carbon cycles between solid and fluid forms.

Jericho’s modeled melt shows how a volatile rich mix keeps that cargo afloat without grinding it to mush. The same physics explains why some pipes are packed with mantle fragments while others are sparse.

Because the chemistry changes during ascent, the rocks found at the surface can mislead. Models that rewind those changes help recover the melt’s original make up.

Those reconstructions matter for understanding carbon storage at depth and the timing of diamond growth. They also guide which pipes are worth a closer look.

Lessons from kimberlite

Kimberlites are the primary source of mined diamonds worldwide and their behavior shapes exploration strategy. If a pipe lacked enough carbon dioxide early on, it might never have erupted.

Knowing the gas threshold helps explain why some targets fail despite promising clues. It also suggests where to hunt within old continents that still hide deep rooted pipes.

This study links tiny atomic motions to continent scale eruptions. The next steps will test whether other pipes share Jericho’s recipe or follow their own.

The study is published in Geology.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–