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Science 21 September 2007:
Vol. 317. no. 5845, pp. 1740 - 1743
DOI: 10.1126/science.1144997
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Reports

Spin Transition Zone in Earth's Lower Mantle

Jung-Fu Lin,1 György Vankó,2,3 Steven D. Jacobsen,4 Valentin Iota,1 Viktor V. Struzhkin,5 Vitali B. Prakapenka,6 Alexei Kuznetsov,6 Choong-Shik Yoo1*

Mineral properties in Earth's lower mantle are affected by iron electronic states, but representative pressures and temperatures have not yet been probed. Spin states of iron in lower-mantle ferropericlase have been measured up to 95 gigapascals and 2000 kelvin with x-ray emission in a laser-heated diamond cell. A gradual spin transition of iron occurs over a pressure-temperature range extending from about 1000 kilometers in depth and 1900 kelvin to 2200 kilometers and 2300 kelvin in the lower mantle. Because low-spin ferropericlase exhibits higher density and faster sound velocities relative to the high-spin ferropericlase, the observed increase in low-spin (Mg,Fe)O at mid-lower mantle conditions would manifest seismically as a lower-mantle spin transition zone characterized by a steeper-than-normal density gradient.

1 Lawrence Livermore National Laboratory (LLNL), 7000 East Avenue, Livermore, CA 94550, USA.
2 KFKI Research Institute for Particle and Nuclear Physics, Post Office Box 49, H-1525 Budapest, Hungary.
3 European Synchrotron Radiation Facility, Boîte Postal 220 F-38043, Grenoble Cedex 9, France.
4 Department of Earth and Planetary Sciences, Northwestern University, Evanston, IL 60208, USA.
5 Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, DC 20015, USA.
6 Consortium for Advanced Radiation Sources, University of Chicago, Chicago, IL 60637, USA.

* Present address: Department of Chemistry and Institute for Shock Physics, Washington State University, Pullman, WA 99164, USA.

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
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Elastic Shear Anisotropy of Ferropericlase in Earth's Lower Mantle.
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Synchrotron Mossbauer spectroscopic study of ferropericlase at high pressures and temperatures.
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S. D. Jacobsen, C. M. Holl, K. A. Adams, R. A. Fischer, E. S. Martin, C. R. Bina, J.-F. Lin, V. B. Prakapenka, A. Kubo, and P. Dera (2008)
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Elasticity of (Mg,Fe)O Through the Spin Transition of Iron in the Lower Mantle.
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