Intermediate-spin ferrous iron in lowermost mantle post-perovskite and perovskite

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Abstract

Iron-bearing silicate post-perovskite and perovskite are believed to be the dominant minerals of the lowermost mantle and the lower mantle, respectively. The electronic spin state of iron—a quantum property of every electron associated with its angular momentum—can strongly influence the properties of these mineral phases and thereby the nature of the Earth’s interior1,2,3,4,5,6,7,8,9,10,11,12,13,14,15. However, the spin state of iron at lowermost-mantle pressure/temperature conditions is poorly known16,17,18,19,20,21,22,23,24,25,26,27. Here we use in situ X-ray emission, X-ray diffraction and synchrotron Mössbauer spectroscopic techniques to measure the spin and valence states of iron in post-perovskite and perovskite at conditions relevant to the lowermost mantle25,28. We find that Fe2+ exists predominantly in the intermediate-spin state with a total spin number of one in both phases. We conclude that changes in the radiative thermal conductivity and iron partitioning in the lowermost mantle would thus be controlled by the structural transition from perovskite to post-perovskite, rather than the electronic transition of Fe2+.

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Figure 1: X-ray emission spectra of iron.
Figure 2: Representative X-ray diffraction patterns.
Figure 3: Average spin number of Fe2+.
Figure 4: Representative synchrotron Mössbauer spectra.

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Acknowledgements

We acknowledge GSECARS and XOR-3, APS, ANL for the use of the synchrotron and laser facilities. We thank J. Nalibof, E. J. Garnero, B. Maddox, W. Sturhahn, J. Lassiter and S. Grand for helpful discussions. Use of the Advanced Photon Source was supported by US Department of Energy, Office of Science, Basic Energy Sciences, under contract No. DE-AC02-06CH11357. GSECARS is supported by NSF Earth Sciences (EAR-0622171) and DOE Geosciences (DE-FG02-94ER14466). This work at Lawrence Livermore National Laboratory was carried out under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. J.F.L. was partially supported by the Lawrence Livermore Fellowship. G.V. acknowledges financial support from the Hungarian Research Fund (OTKA) under contract No. K72597 and from the Bolyai Fellowship. V.V.S. acknowledges financial support from DOE.

Author information

J.F.L., V.B.P., P.D., V.V.S. and A.K. contributed to the X-ray emission experiments, and J.F.L., E.E.A. and J.Z. contributed to the Mössbauer experiments. H.W. synthesized the starting sample. G.V. and E.E.A. contributed to X-ray emission and Mössbauer data analyses, respectively. All authors participated in the writing and revision of the paper.

Correspondence to Jung-Fu Lin.

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Supplementary Information

Supplementary figures S1-S6 and table S1 (PDF 356 kb)

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Lin, J., Watson, H., Vankó, G. et al. Intermediate-spin ferrous iron in lowermost mantle post-perovskite and perovskite. Nature Geosci 1, 688–691 (2008) doi:10.1038/ngeo310

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