Washington, DC, 15 September 2011- New research provides direct evidence that the carbon from the Earth's surface can cycle deep into the mantle and then brought back.

The study shows that subducted oceanic crust can enters the lower mantle, that crustal material is exhumed and carried from its origin to the shallow upper mantle.This is likely accomplished via a mantle plume. Until now primary petrologic evidence has been missing to establish recycling of deep carbon.

The research team, includes Carnegie scientists, Andrew Steele, Steven Shirey, Eloise Gaillou, J Wang, was led by Michael Walter, a former postdoctoral fellow at the Geophysical Laboratory and his team at the University of Bristol.  The group analyzed super-deep diamonds from Juina-5 kimberlite, Brazil and found that 4 had a unique carbon isotope never before seen in diamonds from the lower mantle. These isotopic compositions are consistent with an origin of the carbon in oceanic crust. These results mean that recycling of crustal materials, including carbon, are not limited to the upper mantle but extends into the lower mantle.
This research provides the first direct evidence that slabs of ocean crust are subducted into the lower mantle and that material, including carbon, is cycled between Earth’s surface and its depths.

This study can be found at:  M. J. Walter et al., Science, 10.1126, 1209300 (2011)

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