Diamonds show Earth still capable of 'superhot' surprises

Diamonds can be categorised by their inclusions:

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minerals trapped within the carbon crystal structure that give clues about the conditions and the rocks in which they formed. The studied diamonds contain harzburgitic inclusions, a type of peridotite ‒ the most common rock in Earth's mantle ‒ which have experienced extreme temperatures and undergone very large amounts of melting.

The study led by researchers at the Vrije Universiteit (VU) Amsterdam used radioisotope analysis to date tiny inclusions trapped in diamonds from the Venetia mine in South Africa. Results showed that the diamonds had formed in at least two separate events. Nine of the diamonds had an age of around 3 billion years, and could be linked to volcanism caused by the break-up of an old continent that led to large-scale melting. However, surprisingly, ten diamonds were dated as just over a billion years old, correlating with a giant volcanic event at Umkondo in southern Zimbabwe, 1.1 billion years ago.

"Conventional thinking has been that the level of melting needed to create these diamonds could only happen early in the history of the Earth when it was much hotter. We show that this is not the case and that some harzburgitic diamonds are much younger than assumed. We propose that our younger set of diamonds formed in a special environment where a major plume from the deep mantle was raised towards the surface and underwent extensive melting as the pressure reduced," said Janne Koornneef, who led the study, published today in Nature Communications.

Read more at: https://phys.org/news/2017-09-diamonds-earth-capable-superhot.html#jCp