Theoretical and experimental evidence for a post-perovskite phase of MgSiO3 in Earth's D'' layer.

Details Theoretical and experimental evidence for a post-perovskite phase of MgSiO3 in Earth's D'' layer. Theoretical and experimental evidence for a post-perovskite phase of MgSiO3 in Earth's D'' layer.

Mar 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005aps..mara11001o&link_type=abstract

American Physical Society, APS March Meeting, March 21-25, 2005, abstract #A11.001

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The Earth's lower mantle, the largest region within our planet (670-2890 km depths), is believed to contain ˜75 vol.% of (Mg,Fe)SiO3 perovskite, ˜20% (Mg,Fe)O, and ˜5% CaSiO3. This mineralogy was unable to explain many unusual properties of the D'' layer, the lowermost ˜150 km of the mantle. Using ab initio simulations and high-pressure experiments we have demonstrated [1] that at pressures and temperatures of the D'' layer, MgSiO3 transforms from perovskite into a layered CaIrO3--type structure (space group Cmcm); this structure was also independently found in [2]. The elastic properties of the new phase and its stability field explain most of the previously puzzling properties of the D'' layer: its seismic anisotropy [3], strongly undulating shear-wave discontinuity at its top^ [4], and the anticorrelation between shear and bulk sound velocities [5]. This new phase is therefore likely to be a major Earth-forming mineral, and its discovery will change our understanding of the deep Earth's interior. Latest studies of the effects of impurities [6,7] on the stability of this phase, and similar phases of other compounds will be discussed. REFERENCES: 1. Oganov A.R., Ono S. (2004). Nature 430, 445-448. 2. Murakami M., et al. (2004). Science 304, 855-858. 3. Panning M., Romanowicz B. (2004). Science 303, 351-353. 4. Sidorin I., et al. D.V. (1999). Science 286, 1326-1331. 5. Su W.J., Dziewonski A.M. (1997). Phys. Earth Planet. Inter. 100, 135-156. 6. Mao W.L., et al. (2004). Proc. Natl. Acad. Sci. 101, 15867-15869. 7. Ono S., Oganov A.R., Ohishi Y. (2004). Submitted.

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