Pressure Dependence of Elastic Wave Velocity for β-Mg <sub>2</sub> SiO <sub>4</sub> and the Composition of the Earth's Mantle

DOI Web Site 被引用文献5件
  • Gabriel D. Gwanmesia
    Mineral Physics Institute and Department of Earth and Space Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794
  • Sally Rigden
    Research School of Earth Sciences, Australian National University, Canberra, A.C.T., 2601, Australia
  • Ian Jackson
    Research School of Earth Sciences, Australian National University, Canberra, A.C.T., 2601, Australia
  • Robert C. Liebermann
    Mineral Physics Institute and Department of Earth and Space Sciences, State University of New York at Stony Brook, Stony Brook, NY 11794

抄録

<jats:p> The pressure dependence of the elastic wave velocities for hot-pressed, elastically isotropic polycrystals of the β (modified spinel) phase of magnesium orthosilicate (Mg <jats:sub>2</jats:sub> SiO <jats:sub>4</jats:sub> ) has been determined at room temperature to 3 gigapascals (GPa) by ultrasonic pulse interferometry. Pressure derivatives of the bulk ( <jats:italic>dK/dP</jats:italic> = 4.8) and shear ( <jats:italic>dG/dP</jats:italic> = 1.7) moduli derived from the travel times of the compressional (P) and shear (S) waves clearly demonstrate that the velocity contrast between the olivine and β phases of Mg <jats:sub>2</jats:sub> SiO <jats:sub>4</jats:sub> decreases with increasing pressure. When combined with plausible values for the (as yet unmeasured) temperature derivatives, these new data can be used to calculate the contrast in P and S wave velocities across an olivine-β phase transformation occurring at pressure-temperature conditions corresponding to about 400 kilometers depth in the earth. The seismologically observed contrasts Δ <jats:italic>V</jats:italic> in both P and S wave velocities constrain the percentage of orthosilicate in a model mantle of uniform chemical composition for appropriate relative magnitudes of the temperature ( <jats:italic>T</jats:italic> ) derivatives of the bulk and shear moduli for the β phase. Allowed combinations of orthosilicate content (percent), <jats:italic>dK/dT</jats:italic> , and <jats:italic>dG/dT</jats:italic> (both in gigapascals per Kelvin) for a pair of recent seismological models with Δ <jats:italic>V</jats:italic> <jats:sub>p</jats:sub> = Δ <jats:italic>V</jats:italic> <jats:sub>s</jats:sub> = 4.6% include (65, -0.018, -0.020), (55, -0.015, -0.018), and (45, -0.012, -0.016). </jats:p>

収録刊行物

  • Science

    Science 250 (4982), 794-797, 1990-11-09

    American Association for the Advancement of Science (AAAS)

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