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Enhancement of Cation Diffusion Rates Across the 410-Kilometer Discontinuity in Earth's Mantle

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Science  15 Jan 1999:
Vol. 283, Issue 5400, pp. 362-365
DOI: 10.1126/science.283.5400.362

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Abstract

Rates of cation diffusion (magnesium, iron, and nickel) have been determined in olivine and its high-pressure polymorph, wadsleyite, at 9 to 15 gigapascals and 1100° to 1400°C for compositions that are relevant to Earth's mantle. Diffusion in olivine becomes strongly dependent on composition at high pressure. In wadsleyite, diffusion is one to two orders of magnitude faster than in olivine, depending on temperature. Homogenization of mantle heterogeneities (chemical mixing) and mineral transformations involving a magnesium-iron exchange will therefore occur considerably faster in the transition zone than at depths of less than 410 kilometers.

  • * To whom correspondence should be addressed. E-mail: Sumit.Chakraborty{at}rz.ruhr-uni-bochum.de

  • Present address: Institut für Mineralogie, Ruhr-Universität Bochum, D-44780 Bochum, Germany.

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