On January 14th, 2016 we learned about

Determining the seafloor points of departure for superdeep diamonds

Some of the rarest diamonds are the result of an enormous, circuitous journey around, and through, the Earth. While hard to trace directly, superdeep diamonds appear to have been largely formed hundreds of miles below the planet’s surface. Some of that process has been recreated in a laboratory, showing that the carbon that eventually surfaces as a hard, sparkly rock likely started it’s trip in the depths of the ocean.

Crushing the carbon

Carbon is found all around the world, largely circulated in the bodies of living things. Some of that carbon becomes airborne, while some accumulates in the oceans (to be further supplemented by all the living bodies already there.) Some of that carbon finds its way to intersections of the Earth’s tectonic plates, which then crush the carbon down, heating it and sending it deeper into the ground in a process called plate subduction. The carbon can move over 400 miles down as it’s further compressed into crystal structures. Eventually the carbon-as-diamonds are pushed back up to the surface where we can see the results.

This cycle hasn’t been directly witnessed in the ground, but chemical souvenirs the diamonds collect along the way tell the story. Minerals are captured as the diamonds are first formed in the subduction process. By comparing components that would have originated from shallower depths to deeper ones, scientists were able to plot the route a diamond would have to take to run into each element. These chemical passengers are then visible in the final product as 10 to 40 micron impurities in the diamonds called incursions.

Simulating seafloor subduction

To confirm how the carbon starts this journey, researchers recently recreated the effects of plat subduction in a lab at the University of Bristol in England. A chamber was built that could generate the enormous pressures and temperatures expected when carbon enters the Earth’s mantle. With the molten slab from this fabricated fissure, the resulting carbon matched what would be necessary to produce a superdeep diamond. With this confirmation, geologists can use the minerals in diamonds’ incursions to learn more about the makeup and activity deep under the ground as those elements are carried up to us.

Source: 'Superdeep' Diamonds Formed From Seawater by Patrick J. Kiger, Discovery News

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