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

doi:doi:10.1038/ngeo310

Nature Geoscience 1, 688 - 691 (2008)
Published online: 14 September 2008 | doi:10.1038/ngeo310

Subject Categories: Structural geology, tectonics and geodynamics | Volcanology, mineralogy and petrology

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

Jung-Fu Lin¹, Heather Watson², György Vankó³, Esen E. Alp⁴, Vitali B. Prakapenka⁵, Przemek Dera⁵, Viktor V. Struzhkin⁶, Atsushi Kubo⁵, Jiyong Zhao⁴, Catherine McCammon⁷ & William J. Evans²

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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 interior^1,^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 known^16,^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 mantle^25,²⁸. 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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Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Texas 78712, USA
Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94550, USA
KFKI Research Institute for Particle and Nuclear Physics, PO Box 49, H-1525 Budapest, Hungary
Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, USA
Consortium for Advanced Radiation Sources, The University of Chicago, Chicago, Illinois 60637, USA
Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC 20015, USA
Bayerisches Geoinstitut, Universität Bayreuth, D-95440 Bayreuth, Germany

Correspondence to: Jung-Fu Lin¹ e-mail: afu@jsg.utexas.edu