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A diamond slice of a South African diamond showing various inclusion-rich zones and laser ablation pits from microanalytical sampling. Yaakov Weiss<\/p>\n
Diamonds preserving chemical reactions <\/p>\n
The Earth\u2019s mantle<\/a> is a massive layer that drives volcanoes, recycles the planet\u2019s crust, and regulates its long-term development. But even at this scale, there are some reactions we can\u2019t see.<\/p>\n Geologists have tried for a long time to understand it, using models and experiments.\u00a0<\/p>\n These models predicted something specific: that at depths of roughly 250 to 300 kilometers, a very special kind of metal should exist.<\/p>\n They believed that nickel-rich metallic alloys would form there. But these predictions were hard to prove due to a lack of natural samples.<\/p>\n The breakthrough finally came from examining nano- and micro-inclusions\u2014tiny imperfections trapped within South Africa\u2019s mine diamonds.\u00a0<\/p>\n These diamonds<\/a> acted as \u201ctiny time capsules,\u201d preserving a rare snapshot of deep Earth processes.<\/p>\n \u201cThis is a rare snapshot of mantle chemistry in action,\u201d said Yaakov Weiss, the study\u2019s lead author.\u00a0<\/p>\n \u201cThe diamonds act as tiny time capsules, preserving a reaction that would otherwise vanish as minerals re-equilibrate with their surroundings,\u201d Weiss added.\u00a0<\/p>\n The inclusions also contained other minerals that confirm the diamonds\u2019 origin in the deep upper mantle and shallow transition zone.<\/p>\n<\/p>\n Diamond formation <\/p>\n The study found the presence of both nickel-iron alloy and nickel-rich carbonate. Normally, these two types of substances would react immediately and not coexist.\u00a0<\/p>\n This surprising coexistence is a critical piece of the puzzle, pointing to a metasomatic redox-freezing reaction.\u00a0The process occurs when an oxidized, carbon-rich melt infiltrates a reduced, metal-bearing mantle rock.\u00a0<\/p>\n The team explained that this interaction created nickel-rich carbonates and oxidized the surrounding mantle rock.<\/p>\n Interestingly, this also shows that diamonds can form from the reaction between carbonate minerals and reduced metals in the mantle.<\/p>\n \u201cIt joins earlier evidence from shallower depths that this is the main mode of formation of natural diamonds,\u201d the researchers noted.<\/p>\n The study supports the theory that diamonds can form when carbonate fluids<\/a> are carried deep into the mantle by subducting tectonic plates and react with metal alloys.\u00a0<\/p>\n Plus, it offers a possible explanation for why some diamonds contain nickel atoms in their crystal structure, a long-standing mystery.<\/p>\n Moreover, the findings provide insights into how volcanoes<\/a> form.<\/p>\n The enrichment of the mantle<\/a> with elements like carbon and potassium during these reactions could be a key step in forming specific volcanic magmas. These magmas, such as kimberlites<\/a>, are responsible for bringing diamonds to the surface.<\/p>\n The research was a collaborative effort with colleagues from the University of Nevada and the University of Cambridge.<\/p>\n