| Summary: | In their recent paper dealing with postspinel transformations in the system Mg2SiO4-Fe2SiO4, Ito and Takahashi [1989] showed that the reaction (Mg,Fe)2SiO4 = (Mg,Fe)SiO3 + (Mg,Fe)O (spinel = perovskite + magnesiowustite) occurs over a very narrow pressure interval, at 1600°C, for values of Fe/(Fe+Mg) of between 0.0 and 0.3. It is the purpose of this comment to point out that the argument for a narrow transition interval can be independently confirmed and strengthened using Ito and Takahashi's data on Fe-Mg partitioning between the phases spinel, perovskite, and magnesiowustite. Ito and Takahashi's contention that the postspinel transition in (Mg,Fe)2SiO4 is sharp enough to produce the major, or sole, contribution to the 670 km discontinuity is reinforced. -from Author
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