文章基本信息

标题：Shear waves in the diamond-anvil cell reveal pressure-induced instability in (Mg,Fe)O
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作者：Steven D. Jacobsen ; Hartmut Spetzler ; Hans J. Reichmann 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2004
卷号：101
期号：16
页码：5867-5871
DOI：10.1073/pnas.0401564101
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The emerging picture of Earth's deep interior from seismic tomography indicates more complexity than previously thought. The presence of lateral anisotropy and heterogeneity in Earth's mantle highlights the need for fully anisotropic elasticity data from mineral physics. A breakthrough in high-frequency (gigahertz) ultrasound has resulted in transmission of pure-mode elastic shear waves into a high-pressure diamond-anvil cell using a P-to-S elastic-wave conversion. The full elastic tensor (cij) of high-pressure minerals or metals can be measured at extreme conditions without optical constraints. Here we report the effects of pressure and composition on shear-wave velocities in the major lower-mantle oxide, magnesiowustite-(Mg,Fe)O. Magnesiowustite containing more than {approx}50% iron exhibits pressure-induced c44 shear-mode softening, indicating an instability in the rocksalt structure. The oxide closer to expected lower-mantle compositions ({approx}20% iron) shows increasing shear velocities more similar to MgO, indicating that it also should have a wide pressure-stability field. A complete sign reversal in the c44 pressure derivative points to a change in the topology of the (Mg,Fe)O phase diagram at {approx}50-60% iron. The relative stability of Mg-rich (Mg,Fe)O and the strong compositional dependence of shear-wave velocities (and {partial}c44/{partial}P) in (Mg,Fe)O implies that seismic heterogeneity in Earth's lower mantle may result from compositional variations rather than phase changes in (Mg,Fe)O.