Learn the History of Supercontinents Through the Formation of Diamonds

According to an article by LiveScience, around 86 million years ago, in the Cretaceous period, a volcanic fissure opened, forming what is today South Africa. Below the surface, the magma traveled hundreds of kilometres shooting rocks and minerals, transporting them to the surface in the form of an avalanche. It is thought that on the surface its appearance was as dramatic as the eruption of Mount Vesuvius.

The result of this explosion, in 1869, was the discovery by a shepherd of a huge shiny rock on the bank of a river. This rock was a huge diamond that would eventually become known as the Star of Africa, and the white hills hid what would become the Kimberley Mine, the epicentre of South Africa's diamond rush.

It is in the Kimberley mine, also known as "The Big Hole", that diamonds known as kimberlites are hidden. These formations, diamonds, are spread across the world, from Ukraine to Siberia and Western Australia, but they are relatively small and rare. What makes them special is the fact that their magmas come from the depths.

The formation of the diamond

Scientists still have doubts about the exact depth, but it is known that they arise beneath the bases of the continents, at the boundary of the hot, convecting mantle. Some may have an even deeper origin, in the transition between the upper and lower mantle. Thus, magmas penetrate very deep and very old rocks, and interact with other processes that only occur deep within the Earth, namely the formation of diamonds.

To crystallise ancient carbon into hard, shiny diamonds requires great pressure, which is why these gems form at least 150 kilometres deep, in the deepest layers of the lithosphere, the scientific term for the relatively rigid crust and upper mantle.

Some, known as sub-lithospheric diamonds, form even deeper, down to around 700 km.

The eruption of diamonds traces the history of supercontinents breaking up

The formation of a diamond could provide a clue about how continents come together. In a study published in October 2023 in the journal Nature, scientists studied diamonds from Brazil and Guinea that formed between 300 and 700 km deep. By dating fluid inclusions within diamonds, it is estimated that diamonds formed about 650 million years ago, when the supercontinent Gondwana was forming.

The diamonds were probably trapped at the base of the continent and remained there for millennia, until Gondwana broke up during the Cretaceous period and kimberlites brought them to the surface. According to Suzzete Timmerman, the importance of these super-deep diamonds was that they helped explain how continents grow. Supercontinents are built when oceanic crust pushes against continental crust.

This process, called subduction, brings two continents together on opposite sides of an ocean. This same subduction takes carbon to the depths, where it can be compressed and turned into diamond. However, according to her, there are still many questions to which they have not yet found answers, such as, for example, scientists still do not know how plates change the bases of supercontinents and whether this affects the time that a supercontinent lasts before come undone.

To get to those answers, researchers will have to improve their ability to determine the age of diamonds by finding more diamonds that are both ancient and from the depths.

Article reference:
Timmerman, S. et al. (2023) Sublithospheric diamond ages and the supercontinent cycle