Diamonds unearthed from South Africa's Voorspoed mine are providing scientists with the first direct natural evidence of nickel-rich metallic alloys deep within Earth's mantle. These remarkable findings, published in Nature Geoscience, stem from research led by Yael Kempe and Yaakov Weiss of the Hebrew University's Institute of Earth Sciences. The study analyzed diamonds formed between 280 and 470 kilometers beneath the planet's surface, revealing nickel-iron metallic nanoinclusions and nickel-rich carbonate microinclusions.
This discovery validates decades of theoretical predictions and high-pressure experiments that suggested the existence of such alloys at these depths, previously lacking natural confirmation. The presence of both nickel-iron alloys and nickel-rich carbonates within the diamonds points to a significant geological process known as a metasomatic redox-freezing reaction. This occurs when an oxidized carbonatitic-silicic melt infiltrates reduced, metal-bearing peridotite.
The interaction captures a crucial moment in Earth's geological history, transforming reduced mantle rock into a more oxidized, volatile-rich domain and simultaneously facilitating diamond formation. These findings have profound implications for our understanding of mantle dynamics and the genesis of various magma types. The localized oxidation of mantle portions, as evidenced by these inclusions, may explain why some superdeep diamonds exhibit unexpectedly high oxidized conditions.
Furthermore, this research sheds light on the origins of volatile-rich magmas, suggesting that the enrichment of mantle peridotite with elements like carbonate and potassium during these redox events can prime the mantle for the subsequent formation of magmas such as kimberlites and certain ocean island basalts. Diamonds, often admired for their beauty, are proving to be invaluable scientific tools. Their internal inclusions, even at the nanometer scale, serve as a natural archive of conditions hundreds of kilometers below the Earth's surface. The ongoing study of these mineral time capsules promises to unveil more about the intricate chemistry of the mantle and the dynamic processes that continue to shape our planet. This research also highlights the interconnectedness of deep Earth processes. The very reactions that create these unique diamond inclusions are linked to the broader geological forces that drive volcanism and shape continents. By studying these ancient records, scientists gain a deeper appreciation for the continuous transformation occurring within our planet's interior.