Washington, Sept 16 (ANI): Scientists have found that the carbon cycle, upon which most living things depend, reaches much deeper into the Earth than generally supposed, all the way to the lower mantle, after analysing the chemistry of an unusual set of Brazilian diamonds.
Michael Walter of the University of Bristol and colleagues in Brazil and the United States analysed a set of "superdeep" diamonds from the Juina kimberlite field in Brazil.
Most diamonds excavated at Earth's surface originated at depths of less than 200 kilometres.
The Juina-5 diamonds studied by Walter and colleagues contain inclusions whose bulk compositions span the range of minerals expected to form when basalt melts and crystallizes under the extreme high pressures and temperatures of the lower mantle.
Thus, these inclusions probably originated when diamond-forming fluids incorporated basaltic components from oceanic lithosphere that had descended into the lower mantle, the researchers have concluded.
If this hypothesis is correct, then the carbon from which the diamonds formed may have been deposited originally within ocean crust at the seafloor.
A relative abundance of light carbon isotopes in the Juina-5 diamonds supports this idea, since this lighter form of carbon is found at the surface but not generally in the mantle, the researchers said.
The diamond inclusions also include separate phases that appear to have "unmixed" from the homogenous pool of material. This unmixing likely happened as the diamonds travelled upward hundreds of kilometres into the upper mantle, they added.
After the diamonds formed in the lower mantle, they may have been launched back near the surface by a rising mantle plume, Walter and colleagues proposed.
The findings will be published online by the journal Science, at the Science Express Web site, on 15 September. (ANI)
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