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Friday, 20 July 2018

Massive diamond cache detected deep in Earth’s interior

There may be more than a quadrillion tons of diamond hidden in the Earth’s interior, according to a new study from MIT and other universities. But the new results are unlikely to set off a diamond rush. The scientists estimate the precious minerals are buried more than 100 miles below the surface, far deeper than any drilling expedition has ever reached.
The ultradeep cache may be scattered within cratonic roots — the oldest and most immovable sections of rock that lie beneath the centre of most continental tectonic plates. Shaped like inverted mountains, cratons can stretch as deep as 200 miles through the Earth’s crust and into its mantle; geologists refer to their deepest sections as “roots.”
In the new study, scientists estimate that cratonic roots may contain 1 to 2 percent diamond. Considering the total volume of cratonic roots in the Earth, the team figures that about a quadrillion (1016) tons of diamond are scattered within these ancient rocks, 90 to 150 miles below the surface.   
“This shows that diamond is not perhaps this exotic mineral, but on the [geological] scale of things, it’s relatively common. We can’t get at them, but still, there is much more diamond there than we have ever thought before,” said Ulrich Faul, a research scientist in MIT’s Department of Earth, Atmospheric, and Planetary Sciences.
Using seismic data to map the Earth’s interior, scientists have been unable to explain a curious anomaly: Sound waves tend to speed up significantly when passing through the roots of ancient cratons. Cratons are known to be colder and less dense than the surrounding mantle, which would in turn yield slightly faster sound waves, but not quite as fast as what has been measured.
The team aimed to identify the composition of cratonic roots that might explain the spikes in seismic speeds. To do this, seismologists on the team first used seismic data from the USGS and other sources to generate a three-dimensional model of the velocities of seismic waves travelling through the Earth’s major cratons.

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