by Edgar Soto/Unsplash
“A diamond is forever.” This iconic slogan, coined for a very successful advertising campaign in the 1940s, sold these stones as a symbol of eternal commitment and unity.
But new research, published in Nature, suggests diamonds could also be a sign of separation, i.e. Earth’s tectonic plates. And it might even give you clues on where to look for them.
Diamonds, being the hardest natural stones, require intense pressure and temperature to form. These conditions are only achieved deep within the Earth. So how do they rise to the surface?
Diamonds are transported in molten rocks, or magmas, called kimberlites. Until now, we didn’t know what process causes kimberlites to suddenly emerge through the earth’s crust after millions or even billions of years hidden beneath continents.
supercontinent cycles
Most geologists agree that explosive eruptions that release diamonds occur in sync with the supercontinent cycle: a recurring pattern of landmass formation and break-up that has defined billions of years of Earth history.
However, the exact mechanisms underlying this relationship are debated. Two main theories have emerged.
It is proposed that kimberlite magmas exploring the “wounds” created when the earth’s crust is stretched or when tectonic plates pull apart. The other theory involves mantle plumes, which are colossal rises of molten rock from the boundary between the core and the mantle, located about 2900 km deep.
Both ideas, however, are not without their problems. First, the main part of the tectonic plate, known as the lithosphere, it is incredibly strong and stable. This makes it difficult for fractures to penetrate, allowing magma to flow.
Additionally, many kimberlites lack the chemical “flavors” one would expect to find in rocks derived from mantle plumes.
In contrast, kimberlite formation is thought to involve extremely low degrees of melting of mantle rocks, often less than 1%. So another mechanism is needed. The new study offers a possible solution to this longstanding conundrum.
The authors used statistical analyses, with the help of artificial intelligence (AI), to forensically examine the link between continental separation and kimberlite volcanism. The overall results showed that the eruptions of most Qimberlite volcanoes occurred between 20 and 30 million years later the tectonic separation of the Earth’s continents.
Moreover, the regional study covering the three continents where the most kimberlites are found – Africa, South America and North America – supported this finding and added a major clue: kimberlite eruptions. . tend to migrate gradually from continental edges to interiors over time, at a uniform rate from continent to continent.
This raises the question: what geological process could explain these patterns? To answer this question, scientists used several computer models to capture the complex behavior of the continents.
domino effect
The authors suggest that a domino effect could explain how the separation of continents ultimately leads to the formation of kimberlite magma. Upon separation, a small continental root region—areas of thick rock beneath some continents— is disturbed and sinks in the underlying mantle.
Here the cooler material sinks and the warm mantle rises, causing a process called boundary driven convection. Models show that this convection triggers similar flow patterns that migrate beneath the nearby continent.
Models show that sweeping across the continental root, these disruptive flows remove a substantial amount of rockseveral tens of kilometers thick, from the base of the continental plate.
Several other computer model results show that this process can gather the necessary ingredients in just the right amount to cause just enough melting to generate gas-rich kimberlites. Once formed, and with great buoyancy provided by carbon dioxide and water, magma can quickly rise to the surface.
Find new diamond deposits
This model does not contradict the spatial association between kimberlites and mantle plumes. Rather, the separation of tectonic plates may or may not result from the heating, thinning, and weakening of the plate caused by plumes.
However, the research clearly shows that the spatial, temporal and chemical patterns observed in most kimberlite-rich regions cannot be adequately explained by the presence of plumes alone.
The processes that trigger the eruptions that bring diamonds to the surface appear to be very systematic. They start at the edges of continents and migrate inland at a relatively even rate.
This information can be used to identify possible locations and times of past volcanic eruptions related to this process, providing clues that could allow the discovery of diamond deposits and other rare elements necessary for the transition to green energies.
