Fountains of diamonds, emerging from the Earth’s core, are uncovering the forgotten narrative of supercontinents. The ascent of diamonds to the Earth’s surface occurs during colossal volcanic eruptions accompanying the breakup of supercontinents, and their formation is linked to the amalgamation of continents. Approximately 86 million years ago, during the twilight of the Cretaceous period, a volcanic vent in present-day South Africa became active. Below the surface, magma surged upward, devouring rocks and minerals from hundreds of miles below, creating a reverse avalanche.
While the spectacle of this event remains lost in history, the aftermath manifested as carrot-shaped tubes beneath weathered white hills, filled with igneous rocks. In 1869, a shepherd’s discovery of a massive, glittering rock near a riverbank marked the beginning of the Star of Africa, an enormous diamond. This discovery led to the establishment of the Kimberley Mine, nicknamed “The Big Hole,” which became the epicenter of South Africa’s diamond rush.
The formations where diamonds are discovered, now termed kimberlites, owe their name to the Kimberley Mine. Although kimberlites are scattered globally, from Ukraine to Siberia to Western Australia, they are relatively small and rare. Their uniqueness lies in the fact that their magmas originate from profound depths, beneath the continental bases in the hot, convecting mantle, and possibly even deeper, at the upper and lower mantle transition.
These magmas, tapping into ancient rock layers, undergo processes specific to the deep Earth, including diamond formation. Diamonds crystallize from carbon under intense pressure, forming at least 93 miles (150 kilometers) below the Earth’s surface. Some, known as sub-lithospheric diamonds, form even deeper, around 435 miles (700 km). Kimberlites, on their journey to the surface, trap diamonds, bringing them relatively intact, and sometimes even containing mantle fluid pockets.
Scientific understanding has traditionally acknowledged the downward movement of carbon during tectonic plate interactions, but recent insights suggest that carbon, now transformed into dazzling gems, also resurfaces, particularly during supercontinent breakup events. Kimberlite eruptions, associated with these events, provide a unique perspective on the supercontinent life cycle.
The challenge lies in studying kimberlites due to their scarcity and the rapid weathering of their main component, olivine, on the surface. Recent studies suggest a connection between kimberlite pulses and the timing of supercontinent breakups. Kimberlite eruptions were notably prevalent during the breakup of Nuna, Rodinia, and Pangaea, indicating a correlation between supercontinent cycles and kimberlite activity.
Although no one has directly witnessed a kimberlite eruption, computer modeling has shed light on the process. Rifting, where continental crust pulls apart, is crucial for creating the conditions necessary for kimberlite eruption. This process generates eddies at the surface and base of the continent, allowing the buoyant and high-velocity kimberlites to ascend, carrying diamonds encountered on their way up.
The chemistry of kimberlites differs significantly from the mantle rock they originate from, containing volatiles like water and carbon dioxide, making them eruptive. Kimberlites move through the crust at remarkable speeds, reaching up to 83 mph (134 km/h), in contrast to other magmas from volcanoes like Hawaii.
Recent studies, including one from August 2023, propose that kimberlites can breach the thick hearts of continents through the process of rifting. This involves continental crust stretching apart, creating peaks and valleys that allow mantle materials to rise, forming kimberlite magma. The march of kimberlites into stable crust areas explains why kimberlite pulses follow significant supercontinent breakups.
Diamonds carried within kimberlites, unlike the quickly weathering kimberlites themselves, provide valuable insights. Microscopic fluid pockets within diamonds offer glimpses into the mantle’s history, dating back hundreds of millions to billions of years. These diamonds, formed deep within the Earth, can carry materials from as far down as the mantle-core boundary.
Research on deep diamonds from Brazil and Guinea suggests a connection between diamond formation and the growth of supercontinents. Diamonds formed around 650 million years ago, during the formation of the supercontinent Gondwana, stayed at the continent’s base for millennia, and resurfaced during the Cretaceous period when Gondwana broke apart.
Superdeep diamonds can elucidate subduction processes, mantle convection, and other phenomena occurring beneath the crust during supercontinent cycles. They may also reveal information about Earth’s ancient history, including the incorporation of carbon during its formation and the emergence of life in the oceans.
While many questions remain unanswered, ongoing research aims to unravel the mysteries hidden within ancient diamonds, providing a unique perspective on Earth’s dynamic past.
