HR: 14:55h
AN: MR53A-06    [Abstracts]
TI: Ultrasonic elastic wave velocity measurements of MgO at high pressures and high temperatures with standard-free pressure calibration
AU: * Kono, Y
EM: kono@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577, Japan
AU: Higo, Y
EM: higo@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577, Japan
AU: Inoue, T
EM: inoue@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577, Japan
AU: Irifune, T
EM: irifune@sci.ehime-u.ac.jp
AF: Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 790-8577, Japan
AB: Pressure determination in high-pressure X-ray diffraction experiment is one of the most crucial uncertainties for determining the location of phase transition in the Earthfs deep interiors. MgO is frequently used as a pressure standard using the previously published equation-of-state, while pressure calibration for determining the equation-of-state remains unsolved because of the lack of direct measurement of sample pressure. Here we carried out high pressure X-ray diffraction experiments combined with ultrasonic elastic wave velocity measurement up to 1650 K and 17.7 GPa of NaCl scale (Decker, 1971), and determined sample pressure without pressure standard. High-pressure experiment was carried out using the Kawai-type apparatus (SPEED-1500) in BL04B1 beamline at SPring-8. The unit cell volume of MgO, Au, and NaCl and resultant their densities were determined from X-ray diffraction measurements. Elastic wave velocities of MgO were determined from elastic wave travel time and sample length which was measured using X-ray radiography. Adiabatic bulk modulus of MgO at each pressures and temperatures were determined using the observed compressional and shear wave velocities, and density. Then we determined zero pressure isothermal bulk modulus and its pressure and temperature derivatives with fixed zero pressure thermal expansion coefficient, Gruneisen parameter and its volume dependence, and calculated pressure using the Birch-Murnaghan equation of state. Our derived pressures at 300 K are consistent with those calculated with the Au (Anderson et al., 1989) and NaCl (Decker, 1971) scale up to ~10 GPa, while is higher than those of Au and NaCl scale above ~10 GPa. The difference of pressure from the Au and NaCl scale continuously increases with increasing pressure, and reaches to ~1GPa at ~16-18 GPa. At high temperatures we also observed difference in pressure between our equation- of-state and the scale of Anderson et al. (1989) and Decker (1971) above ~10 GPa. The misunderstanding in pressure derived from the Au and NaCl scale would give significant influence on understanding the depth of phase transition in the Earthfs deep interiors.
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 7208 Mantle (1212, 1213, 8124)
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting