Geologists Discover Key Substance Behind Diamonds Rising to Earth's Surface

A groundbreaking study, recently published in Geology, has uncovered the vital role of carbon dioxide in the journey of diamonds from deep within the Earth’s mantle to the surface. The research, led by Ana Anzulović from the University of Oslo, explores the complex behavior of kimberlite magma, the rare volcanic rock that carries diamonds.
The Crucial Role of Carbon Dioxide in Kimberlite Magma Ascent
One of the most significant discoveries from this study revolves around the amount of carbon dioxide needed to allow kimberlite to rise from the depths of the Earth. Ana Anzulović and her team found that a minimum of 8.2% carbon dioxide is required for kimberlite magma to remain buoyant enough to travel upwards. Without sufficient carbon dioxide, the magma would become denser than the surrounding rock, causing it to stall before reaching the surface. As Anzulović explains,
“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.”
In their simulations, the team modeled various mixtures of water and carbon dioxide to determine how they impacted the buoyancy of the magma. The results revealed that the presence of these volatile compounds is essential in preventing the magma from sinking back into the Earth. This finding not only enhances our understanding of diamond transport but also helps geologists better predict which kimberlite pipes are more likely to contain diamonds, thus improving exploration strategies.
How Kimberlite Magma Carries Diamonds: The Science Behind the Ascent
Kimberlite magma’s ability to transport diamonds is a result of its unique properties and the conditions under which it forms. Unlike most volcanic rocks, kimberlite originates from the Earth’s mantle, a vast and extremely hot layer of the planet beneath the crust. This magma is rich in volatiles, including water and carbon dioxide, which play a critical role in its behavior as it rises through the crust. The process begins when kimberlite magma starts to melt from the mantle, carrying with it a variety of materials from deep within the Earth, including diamonds.
In their analysis, Anzulović and her team focused on how the presence of dissolved gases like water and carbon dioxide affected the magma’s movement. Water helps to lower the viscosity of the magma, allowing it to flow more easily, while carbon dioxide helps strengthen the magma at greater depths. Together, these gases enable the magma to ascend rapidly, preventing diamonds from turning into graphite, which is a more stable form of carbon at shallow depths. As the magma rises and cools quickly upon reaching the surface, it traps the diamonds inside, preserving their structure and allowing them to be collected in kimberlite pipes.
The Jericho Kimberlite Pipe: A Case Study in Diamond Transport
The Jericho kimberlite pipe in northern Canada provided the perfect case study for this research. Located in the Slave craton, one of the oldest and most stable parts of Earth’s crust, the Jericho pipe has long been known as a source of diamonds. The study’s focus on this specific kimberlite allowed the researchers to conduct detailed simulations of how the magma ascended through the Earth’s crust and carried diamonds along the way. According to 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.”