Predominant Intermediate-Spin Ferrous Iron in Lowermost Mantle Post-Perovskite and Perovskite
Abstract
Silicate post-perovskite and perovskite are believed to be the dominant minerals of the lowermost mantle and the lower mantle, respectively, and their properties, which can be strongly influenced by the electronic state of iron in these phases, affect our understanding of the nature of the deep Earth. To date, in these minerals the electronic spin state of iron remains unknown under lowermost-mantle pressure-temperature conditions, although recent studies have showed an electronic spin crossover from high-spin to low-spin in ferropericlase over an extended pressure-temperature range of the lower mantle (i.e., Lin et al., Science, 2007) and from high-spin to intermediate-spin in silicate perovskite near the top of the lower mantle (McCammon et al., Nature Geoscience, 2008). Here we report the spin and valence states of iron in post-perovskite and perovskite at pressure-temperature conditions relevant to the lowermost mantle using in situ X-ray emission, X-ray diffraction, and synchrotron Mossbauer spectroscopies in a laser-heated diamond cell. Perovskite and post-perovskite display extremely high quadrupole splitting (QS) of approximately 4 mm/s and relatively high center shift in the synchrotron Mossbauer spectra at 110 GPa and 134 GPa, respectively. Our results show that Fe2+ exists predominantly in the intermediate-spin state with a total spin number of one in both phases (Lin et al., Nature Geoscience, 2008). Together with recent results on the effects of the spin transition in the lower-mantle ferropericlase (see a recent review by Lin and Tsuchiya, PEPI, 2008), here we will address how the electronic spin states in lower-mantle phases and their associated effects affect our understanding on the composition, geophysics, and dynamics of the lower mantle.. References: 1. Lin, J. F., H. C. Watson, G. Vanko, E. E. Alp, V. B. Prakapenka, P. Dera, V. V. Struzhkin, A. Kubo, J. Zhao, C. McCammon, W. J. Evans, Intermediate-spin ferrous iron in lowermost mantle post-perovskite and perovskite, Nature Geosciences, 2008. 2. Lin, J. F., and T. Tsuchiya, Spin transition of iron in the Earth's lower mantle, Phys. Earth Planet. Inter., doi:10.1016/j.pepi.2008.01.005, 2008. 3. Lin, J. F., G. Vanko, S. D. Jacobsen, V. Iota-Herbei, V. V. Struzhkin, V. B. Prakapenka, A. Kuznetsov, and C.-S.Yoo, Spin transition zone in Earth's lower mantle, Science, 317, 1740-1743, 2007.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMMR31A1821L
- Keywords:
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- 3620 Mineral and crystal chemistry (1042);
- 3630 Experimental mineralogy and petrology;
- 3900 MINERAL PHYSICS;
- 3924 High-pressure behavior;
- 3954 X-ray;
- neutron;
- and electron spectroscopy and diffraction