Enhancement of cation diffusion rates across the 410-kilometer discontinuity in Earth's mantle
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 degrees to 1400 degreesC 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.
Chakraborty
S
S. Chakraborty, Institut fur Mineralogie und Geochemie, Universit at zu Koln, Zulpicher Strasse 49B, 50674 Koln, Germany. R. Knoche, Institut fur Mineralogie und Petrographie, Universitat Innsbruck, Innrain 52, A-6020, Innsbruck, Austria. H. Sch.
Knoche
R
Schulze
H
Rubie
DC
Dobson
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Ross
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Angel
RJ