New Research Quantifies Reaction behind Sub-Lithospheric Diamonds

Loose Diamonds
Interesting Diamond Facts

A new research suggests that quick reactions between the Earth’s mantle and subducted tectonic plates at specific depths are responsible for forming the most valuable diamonds. The most-often mined diamonds are formed at depths of about 93 to 155 miles in the mantle of the Earth. They are formed by way of extreme pressure as well as a high temperature of 1050 degrees Celsius, at the least. Only a small quantity of them make it to regions where they can be mined though, because a majority of the rocks get destroyed in the journey to the crust of the Earth through deep source eruptions.

They recent study said that a small portion of excavated diamonds, called superdeep or sub-lithospheric diamonds, are actually formed at deeper depths, mostly in diamond-rich zones at depths of 155 to 279 miles and 372 to 497 miles. They stand out from other diamonds owing to their composition, which occasionally comprise materials from the Earth such as majorite garnet, bridgmanite, and ferropericlase.

According to Feng Zhu, who is the lead author of the study, “Although only composing 1 percent of the total mined diamonds, it seems lots of large and high-purity diamonds are superdeep diamonds, so they have good value as gems.” The study is published in the journal, “Geophysical Research Letters”. Feng Zhu was University of Michigan’s post-doctoral researcher when he conducted this research.

No earlier theory has fully explained why very few stones have been found adjacent to the surface area at depths of 372 to 497 miles – the area amid the zones is where sub-lithospheric diamonds are formed the most.

The new study is seeking to explain the reason behind this phenomenon. Feng Zhu, who is now University of Hawai’I’s post-doctoral researcher, and his colleagues, feel the super deep areas are rich in diamonds owing to the high production rates. It explains what drives the diamonds-forming reaction in a few areas and what slows the process down in other areas.

The researchers said that diamonds can form anywhere in the Earth’s mantle, extending from around 21 to 1,800 miles below the surface of the Earth. However, miners seldom see most of them in loose diamonds form. Very few diamonds actually survive the volcanic voyage to the crust of the Earth where the miners can sample them.

That means the odds of finding diamonds from very deep areas in the mantle, forming relatively few diamonds, is very small. Just one percent of excavated diamonds actually come from those regions.

 

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