X-rays of diamonds used as windows to Earth?s center

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A team of researchers have gained a deeper insight into how the Earth recycles itself in the deep earth tectonic cycle way utilizing synchrotron x-ray beams, according to research published in the July 31 issue of Nature.

The Earth's oceanic crust is constantly renewed in a cycle which has been occurring for billions of years. Seismic imaging suggests that the oceanic crust can be subducted to depths of almost 3000 km below the Earth's surface, during which time the crust material develops its own unique 'flavor' in comparison with the surrounding magmas. The exact nature of how this happens has remained unclear for years.

Researchers at the University of Bristol in England, working alongside colleagues at the STFC Daresbury Laboratory in Warrington, England, said that they have now discovered the answer by looking at diamonds from the Juina area of Brazil.

As the carbonate-rich magma rises through the Earth’s mantle, diamonds crystallize, trapping minute quantities of minerals in the process. They form at great depths and pressures and therefore can provide clues as to what is happening at the Earth's deep interior, the authors said.

At the Synchrotron Radiation Source (SRS) at the STFC lab, the team used a 7.5 GeV electron synchrotron as a source for diffraction x-rays to look at the conditions of formation for the mineral perovskite which occurs in diamonds but does not occur naturally near the Earth's surface.

With a focused beam, less than half the width of a human hair, researchers used x-ray diffraction techniques to establish the conditions at which perovskite is stable. They concluded that mineral inclusions were formed up to 700 km into the Earth’s mantle’s transition zone.

The results, backed up by further experiments carried out at the University of Edinburgh, the University of Bayreuth in Germany, and the Advanced Light Source in the Berkeley, Calif., enabled the research team to show that the diamonds and their perovskite inclusions had indeed crystallized from very small-degree melts in the Earth's mantle, according to the authors.

Upon heating, oceanic crust forms carbonatite melts, super-concentrated in trace elements with the 'flavor' of the Earth's oceanic crust. Such melts may be widespread throughout the mantle and may have been 'flavoring' the mantle rocks for a very long time, the researchers concluded.