HR: 14:52h
AN: MR23D-07    [Abstracts]
TI: Stability and Equation of State of post-perovskite phase in the system MgSiO3-Al2O3 to 2 Mbar
AU: * Kubo, A
AF: Princeton Univ, Guyot Hall, Princeton, NJ 08544, United States
AU: * Kubo, A
AF: GSECARS, Univ Chicago, 9700 S. Cass Ave, Bldg 434A, Argonne, IL 60439, United States
AU: Duffy, T S
AF: Princeton Univ, Guyot Hall, Princeton, NJ 08544, United States
AU: Shen, G
AF: GSECARS, Univ Chicago, 9700 S. Cass Ave, Bldg 434A, Argonne, IL 60439, United States
AU: Shen, G
AF: HPCAT, Carnegie Institution of Washington, 9700 S. Cass Ave, Bldg 434E, Argonne, IL 60439, United States
AU: Prakapenka, V
AF: GSECARS, Univ Chicago, 9700 S. Cass Ave, Bldg 434A, Argonne, IL 60439, United States
AB: Al2O3 is an important oxide component in the Earthfs interior, and the lower mantle is thought to contain about 5 mol% Al2O3. It is also known that dissolution of the Al2O3 content can affect phase transition pressure and elastic properties of mantle phases. We have studied the effects of Al2O3 content on stability and equation of state of post-perovskite (pPv) phase in MgSiO3 using laser-heated diamond cells. Powdered glasses with the bulk composition of X mol% MgSiO3 and (1-X) mol% Al2O3 (X = 100, 95, 90, and 85) were used as starting materials. They were mixed with Pt powder that served as both a pressure standard and a laser absorber. NaCl was used as a pressure medium. In situ x-ray diffraction experiments at high pressures and temperatures were conducted at GSECARS in Advanced Photon Source using angle-dispersive diffraction and double-sided laser heating. The pPv transition boundary was determined to be 130(2) GPa at 1800 K for X=85. It is likely that the pressure interval of the two-phase stability field (binary roop) of pPv + perovskite is probably a few GPa for X=85, which is inconsistent with both the experimental results for X=75 by Tateno et al. (2005) and theoretical predictions by Akber-Knutson et al. (2005). Pressure (P) -volume (V) data for the pPv phase were obtained for all the single- phase pPv with respective bulk compositions up to 2 Mbar. By fitting the P-V data of the pPv phase with X=95 at 123 - 180 GPa to the 2nd order Birch-Murnaghan equation of state with the reference state set to 120 GPa, bulk modulus at 120 GPa was determined to be 602(21) GPa. Contrary to the case for the perovskite phase in the MgSiO3-Al2O3 system, systematic trend between P-V-X for the pPv phase was found to be insignificant, and the pPv phase in this system has the smallest volume as well as pure MgSiO3 among the silicate pPv phases in various compositions investigated so far. By comparing the P-V data for the pPv phase of X=95 composition with those for perovskite phase with the same chemical composition obtained by Walter et al. (2004), it is estimated that the volume reduction associated with the pPv transition with X=95 bulk composition is 3%.
DE: 3900 MINERAL PHYSICS
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting