Using a standard laptop and a rock fragment sourced from a diamond mine's waste heap, two Queensland University of Technology (QUT) researchers were able to resolve a longstanding geological enigma regarding diamond development within the deep foundations of the Earth's ancient continents.
The results of the study, titled "Deep, Ultra-Hot-Melting Residues as Cradles of Mantle Diamond," were published in the esteemed journal Nature.
Using Computer Model To Solve How Diamonds Are Formed
Lead author Ph.D. student Carl Walsh and QUT Professor Balz Kamber and Emma Tomlinson from Trinity College, Ireland, utilized a standard laptop and a piece of rock, garnet harzburgite, from a waste pile of the Kimberley diamond mine to resolve a geological mystery surrounding diamond formation in the deep roots of the Earth's ancient continents, SciTech Daily reported.
Walsh used computer modeling to predict which minerals and melts would be present in the mantle at different temperatures and compared it with the actual minerals and rocks to determine how the roots were formed.
The garnet harzburgite rock was mined between 1871 and 1914 and contained minerals that were entrained in a supersonic volcanic eruption when it was brought to the surface in a kimberlite pipe. The rock was smashed and damaged during its journey. At that time, it's already 3.3 billion years old.
Walsh's research found that the rocks containing diamonds, which must have experienced high temperatures, did not turn into graphite, as was previously believed.
Professor Kamber specializes in petrology and studies rocks and the conditions under which they form. He carefully broke down the rock using a sledgehammer to make it small enough to transport. Their research challenges the existing two-step shallow "melting and stacking" explanation for diamond formation.
Rarity of Diamonds
The second major implication of the research concerns the rarity of diamonds. As per the report of Phys.org, researchers offer an alternative view on what most scientists believe diamonds were not originally rare but were rather destroyed over time as the mantle root was eroded. The new research, on the other hand, suggests that diamonds have always been rare.
The study sought to determine whether the cradles of diamond, which are highly depleted mantle bits in continental roots, were once common and became scarce over time, or whether they have always been scarce.
To evaluate this, the researchers analyzed komatiites, which are preserved fluid lavas that erupted at the continental surface during intense melting events on the early Earth. The model predicted which compositions of komatiite could have formed alongside chromium-rich pyrope garnet.
The researchers found that the particular composition associated with pyrope garnet is rare, occurring in only 8%-28% of komatiites. This suggests that both pyrope garnets and the highly depleted mantle domains from which they originate have always been rare, even on early Earth. Diamonds have an affinity for these rocks, meaning that they too must have always been rare.
As a result, the researchers suggest that the rarity of diamonds is not solely due to their destruction over time, but rather that they have always been scarce. This makes diamonds even more remarkable in their rarity.
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