The effect of bulk composition and temperature on mantle seismic structure
The effect of bulk composition and temperature on mantle seismic structure
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DOI：
10.1016/j.epsl.2008.08.012
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发表时间：
2008-10
影响因子：
5.3
通讯作者：
Wenbo Xu;C. Lithgow‐Bertelloni;L. Stixrude;J. Ritsema
中科院分区：
文献类型：
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作者：
Wenbo Xu;C. Lithgow‐Bertelloni;L. Stixrude;J. Ritsema
本文采用自洽的热力学方法计算了模型地幔组分的相平衡和物理性质，结果表明：（1）由热解组分组成的平衡组合（EA）和（2）由玄武岩和方辉橄榄岩组成的机械混合物（MM）组成的地幔，其地震学性质有很大差异。计算了玄武岩含量从0%到100%，沿着岩带，位温从1000 K到2000 K的EA和MM的密度、纵波速度（VP）和横波速度（VS）。对于MM，VSin的过渡区更大，随着深度的增加而增加得更快，并且对玄武岩分数不敏感，而对于EA，对于<70%的分数，VS随着玄武岩分数的增加而降低2.5%。520公里的不连续的幅度和锐度强烈依赖于温度在EA和MM，这可能解释其地震检测的横向变化。MM和EA都具有复杂的结构，在深度范围640-750公里，由于转变的akimotoite，ringwoodite和石榴石的密集组合。在上地幔，MM比大多数地震学模型快，在下地幔慢，这表明随着深度的增加，地幔中的玄武岩分数。
We use a self-consistent thermodynamic formalism to compute the phase equilibria and physical properties of model mantle compositions, demonstrating that the seismological properties of a mantle comprised of (1) an equilibrium assemblage (EA) of pyrolitic composition and (2) a mechanical mixture (MM) of basalt and harzburgite with identical bulk composition differ significantly. We calculate the density, compressional wave velocity (VP), and shear wave velocity (VS) of EA and MM with basalt fraction varying from 0% to 100% and along adiabats with potential temperatures ranging from 1000 K to 2000 K. For MM, VSin the transition zone is greater, increases more rapidly with depth, and is insensitive to basalt fraction, while for EA VSdecreases by 2.5% with increasing basalt fraction for fractions <70%. The magnitude and sharpness of the 520-km discontinuity depends strongly on temperature in both EA and MM, which may explain lateral variations in its seismic detection. Both MM and EA feature complex structure in the depth range 640–750 km due to the transformations of akimotoite, ringwoodite, and garnet to denser assemblages. MM is faster than most seismological models in the upper mantle, and slower in the lower mantle, suggesting an increase of basalt fraction with depth in the mantle.