While most diamonds form under continents, at depths between 150 and 300 kilometers, a document published in Scientific reports has shown that two rarer types of diamonds – those found in oceanic rocks and those that form more than 300 kilometers below the continental crust – have a common and unexpected origin.
The Curtin University research team found that oceanic and ultra-deep continental diamonds “actually share the same compositions,” according to Dr. Luc Doucet, lead author of the article.
“The composition of carbon is organic, which means that it is the organic matter that formed the diamonds.”
Diamonds are made from carbon placed under high pressure, but this carbon can come from different sources: either organic carbon, from once living matter, or inorganic carbon – like carbonate minerals, which are commonly found in the rocks.
According to Doucet, it’s surprising that diamonds formed so deep below the Earth’s surface are mostly made up of organic matter.
“Particularly in the ocean, organic carbon is very minor [in abundance] compared to inorganic carbon, ”he says.
If ultra-deep diamonds form mostly from organic carbon, Doucet says that means there’s some sort of carbon fixation process going on – or maybe something even more complicated is going on. during their training.
The researchers propose that once formed, these very deep diamonds are brought to the surface via “mantle plumes” – material from the Earth’s mantle rising to the surface.
“Raising rocks from the Earth’s deeper mantle, called mantle plumes, then brings the diamonds back to the Earth’s surface via volcanic eruptions,” says Doucet.
The researchers examined a range of the most common oceanic, deep continental and lithospheric diamonds, each of which were collected and tested in previous studies. They concluded that oceanic and continental diamonds had organic origins by examining their “isotopic signature” – the different concentrations of slightly heavier and lighter carbon atoms in diamonds.
Doucet says this research is useful in understanding how carbon on the surface – and in the atmosphere – can enter the earth. It has particular implications for carbon capture and storage.
“Diamonds are very good targets for understanding what’s going on inside the earth,” he says.
“They’re made of carbon, so they can help us understand carbon cycles. “
Originally posted by Cosmos under the title Deep Diamonds Have a Surprising Organic Composition
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