Iron-rich perovskite in the Earth's lower mantle

Details Iron-rich perovskite in the Earth's lower mantle Iron-rich perovskite in the Earth's lower mantle

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011e%26psl.309..179m&link_type=abstract

Earth and Planetary Science Letters, Volume 309, Issue 3, p. 179-184.

Computer Science

Sound

Fe-Bearing Perovskite, Equation Of State, Lower Mantle, Bulk Sound Velocity, Density

Scientific paper

The equations of state of perovskite with (Mg0.75,Fe0.25)SiO3 and MgSiO3 compositions have been investigated by synchrotron X-ray diffraction up to 130 GPa at 300 K in diamond anvil cells. Here we show that the addition of 25% Fe in MgSiO3 perovskite increases its density and bulk sound velocity (VФ) by 4-6% and 6-7%, respectively, at lower-mantle pressures. Based on concurrent synchrotron X-ray emission and Mössbauer spectroscopic studies of the samples, the increase in VФ and density can be explained by the occurrence of the low-spin Fe3+ and the extremely high-quadrupole component of Fe2+. Combining these experimental results with thermodynamic modeling, our results indicate that iron-rich perovskite can produce an increase in density and a value of VФ that is compatible with seismic observations of reduced shear-wave velocity in regions interpreted as dense, stiff piles in the lower mantle. Therefore, the existence of the Fe-rich perovskite in the lower mantle may help elucidate the cause of the lower-mantle large low-shear-velocity provinces (LLSVPs) where enhanced density and VФ are seismically observed to anti-correlate with the reduced shear wave velocity.

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