Intermediate-spin ferrous iron in lower mantle perovskite
Intermediate-spin ferrous iron in lower mantle perovskite
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下地幔钙钛矿中的中间自旋亚铁
DOI：
10.1038/ngeo309
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
L. Dubrovinsky
中科院分区：
文献类型：
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作者：
C. McCammon;I. Kantor;O. Narygina;J. Rouquette;U. Ponkratz;I. Sergeev;M. Mezouar;V. Prakapenka;L. Dubrovinsky
下地幔主要由具有钙钛矿结构的含镁和含铁矿物组成。铁具有采用不同电子组态的能力，其在下地幔中自旋态的转变可以显著影响地幔性质和动力学。然而，以前的研究，旨在了解这些转变提供了相互矛盾的结果，。在这里，我们报告了高压（高达110 GPa）和高温（高达1,000 K）实验的结果，旨在了解下地幔条件下钙钛矿中铁的自旋跃迁。我们的穆斯堡尔和核前向散射数据的两个下地幔钙钛矿组合物表明，从高自旋到中间自旋状态的二价铁的转变发生在大约30 GPa，高温有利于稳定的中间自旋状态。因此，我们推断，亚铁采取的中间自旋状态，整个下地幔的大部分。我们的X射线数据显示，含有中间自旋亚铁的下地幔钙钛矿具有显著的各向异性压缩，这与自旋跃迁密切相关。我们预测自旋状态的不均匀性在下地幔的最上部与下沉板块和地区的上涌。这些可能影响当地的性质，包括导热性和导电性、变形（粘度）和化学行为，从而影响地幔动力学。
The lower mantle is dominated by a magnesium- and iron-bearing mineral with the perovskite structure. Iron has the ability to adopt different electronic configurations, and transitions in its spin state in the lower mantle can significantly influence mantle properties and dynamics. However, previous studies aimed at understanding these transitions have provided conflicting results,,,. Here we report the results of high-pressure (up to 110 GPa) and high-temperature (up to 1,000 K) experiments aimed at understanding spin transitions of iron in perovskite at lower-mantle conditions. Our Mössbauer and nuclear forward scattering data for two lower-mantle perovskite compositions demonstrate that the transition of ferrous iron from the high-spin to the intermediate-spin state occurs at approximately 30 GPa, and that high temperatures favour the stability of the intermediate-spin state. We therefore infer that ferrous iron adopts the intermediate-spin state throughout the bulk of the lower mantle. Our X-ray data show significant anisotropic compression of lower-mantle perovskite containing intermediate-spin ferrous iron, which correlates strongly with the spin transition. We predict spin-state heterogeneities in the uppermost part of the lower mantle associated with sinking slabs and regions of upwelling. These may affect local properties, including thermal and electrical conductivity, deformation (viscosity) and chemical behaviour, and thereby affect mantle dynamics.