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地球最下地幔中硅酸镁后钙钛矿相的弹性

The elasticity of the MgSiO3 post-perovskite phase in the Earth's lowermost mantle.

作者信息

Iitaka T, Hirose K, Kawamura K, Murakami M

机构信息

Computational Astrophysics Laboratory, RIKEN (The Institute of Physical and Chemical Research), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.

出版信息

Nature. 2004 Jul 22;430(6998):442-5. doi: 10.1038/nature02702.

Abstract

MgSiO3 perovskite has been assumed to be the dominant component of the Earth's lower mantle, although this phase alone cannot explain the discontinuity in seismic velocities observed 200-300 km above the core-mantle boundary (the D" discontinuity) or the polarization anisotropy observed in the lowermost mantle. Experimental and theoretical studies that have attempted to attribute these phenomena to a phase transition in the perovskite phase have tended to simply confirm the stability of the perovskite phase. However, recent in situ X-ray diffraction measurements have revealed a transition to a 'post-perovskite' phase above 125 GPa and 2,500 K--conditions close to those at the D" discontinuity. Here we show the results of first-principles calculations of the structure, stability and elasticity of both phases at zero temperature. We find that the post-perovskite phase becomes the stable phase above 98 GPa, and may be responsible for the observed seismic discontinuity and anisotropy in the lowermost mantle. Although our ground-state calculations of the unit cell do not include the effects of temperature and minor elements, they do provide a consistent explanation for a number of properties of the D" layer.

摘要

硅酸镁钙钛矿被认为是地球下地幔的主要成分,尽管仅这一相无法解释在核幔边界上方200 - 300公里处观测到的地震波速度不连续性(D"不连续性),也无法解释在最底层地幔中观测到的极化各向异性。试图将这些现象归因于钙钛矿相中的相变的实验和理论研究往往只是证实了钙钛矿相的稳定性。然而,最近的原位X射线衍射测量揭示了在125吉帕和2500 K以上会转变为一种“后钙钛矿”相,这些条件接近D"不连续处的条件。在此我们展示了零温度下这两个相的结构、稳定性和弹性的第一性原理计算结果。我们发现后钙钛矿相在98吉帕以上成为稳定相,并且可能是最底层地幔中观测到的地震不连续性和各向异性的原因。尽管我们对晶胞的基态计算没有考虑温度和微量元素的影响,但它们确实为D"层的一些性质提供了一致的解释。

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