When supercontinents break up, diamonds seem to arrive at the surface of the Earth in intense volcanic eruptions. These events take place when continents come together.
Erupting Diamonds
Roughly 86 million years ago, in the Cretaceous period's twilight, a volcanic fissure in present-day South Africa ended up rumbling to life. Under the surface, magma that was hundreds of miles deep upward shot rapidly and chewed up the minerals and rocks, bringing them to the surface in a reverse avalanche.
How this appeared on the surface remains a historical mystery. However, this eruption could have been as dramatic as that of Mount Vesuvius. The remnants were a series of igneous-rock-filled and carrot-shaped tubes beneath weathered and low white hills.
An 1869 discovery of a sparkly and massive rock close to a riverbank would catapult the unseeming landscape into that of infamy. The rock was actually a massive diamond that would eventually be called the Star of Africa. The white hills also hid what ended up becoming the Kimberley Mine, the diamond rush epicenter of South Africa and potentially the largest hole across the planet that was dug by hand.
It is due to the Kimberley Mine, typically called "The Big Hole," that formations where diamonds are spotted are now called kimberlites. These formations can be found all over the world. However, they are quite rare and small. What makes them distinct is that their magmas are from extreme depths.
Questions regarding this depth still remain. Nevertheless, they are known to arise from under continent bases at the border of the mantle. Some may come from even deeper areas, at the transition between the lower and upper mantle.
For a long time, researchers have known that tectonic plates grind beneath each other. They drag down surface carbon to deep areas where it can turn into diamond.
Now, researchers are beginning to see that what goes down at times must go up. The carbon reappearance that is now pressed over gems with glitters is also linked to tectonic plate movements. More specifically, diamonds appear to erupt when supercontinents end up breaking apart.
Supercontinent Breaking
No one has been able to witness an eruption of a kimberlite. Very few have taken place in the last 50 million years. The most recent possible eruption took place more than 10,000 years ago. Not to mention, the main kimberline material quickly weathers away over the surface.
Because of this, kimberlites are difficult to study. Scientists are baffled by the chemistry of the origins of the mantle's melted rocks as well as how kimberlites are able to punch through the core stables of cratons, which are thick interiors of continents that typically resist disruption.
According to Hugo Olierook, a research fellow from Curtin University, continent breakup is fundamental for diamonds to reach the surface from such extreme deaths. Olierook adds that it is extensional forces that enable the little deep-seated magma pockets from reaching the top.
The question lies in how this takes place. There are two primary ingredients for a kimberlite, namely, melted, deep, and fluid-rich rock as well as a continental disruption. No one knows what leads to kimberlite melt formation. However, kimberlite chemistry is very different from that of the mantle rock where it melts from.
In a 2023 study, researchers made use of computer modeling to determine how kimberlites are capable of bursting through thick continent hearts. The scientists discovered that crucial to the rifting process was the pulling apart of the continental crust. This stretching creates valleys and peaks at the continent's base and surface.
At the base, the jagged edges enable mantle materials that are warm to rise, cool, and then fall. This leads to the creation of eddies. The eddies combine materials from the continent's base, leading the buoyant and frothy kimberlites that can shoot towards the surface and bring diamonds up.
The process started right where the rifting of the continent was. However, modeling revealed that the jagged eddy formation regions destabilized areas that neighbored the craton. This created the same dynamics closer to the interior of the continent.
As a result, a kimberlite eruption pattern started near the rift zone but gradually marched into stable crustal areas. According to geologist Thomas Gernon from the University of Southampton, who led the study, the slow march sheds light on why the pulses of kimberlite do not peak until shortly after the massive breakup starts.
Maya Kopylova, a diamond exploration professor from the University of British Columbia, explains that it is only in kimberlites that they can observe samples from 400 to 2,000 kilometers deep. There are no other Earth magmas that are able to do that.
Though diamond eruptions can be traced to a supercontinent breakup story, their formation could also offer hints regarding the coming together of continents.
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