HR: 17:45h
AN: MR14A-08    [Abstracts]
TI: The equation of state of the lower mantle for a pyrolite composition: Implications from the PVT data, PREM and a linear shock-wave Us-Up asumption
AU: * Zhao, H
EM: hzhaos@yahoo.com
AF: Dept. of Geosciences, SUNY at Stony Brook, Stony Brook, NY 11790 United States
AU: Weidner, D J
EM: DWEIDNER@sunysb.edu
AF: Dept. of Geosciences, SUNY at Stony Brook, Stony Brook, NY 11790 United States
AU: Weidner, D J
EM: DWEIDNER@sunysb.edu
AF: Mineral Physics Institute, SUNY at Stony Brook, Stony Brook, NY 11790 United States
AU: Wang, L
EM: liping.wang@sunysb.edu
AF: Mineral Physics Institute, SUNY at Stony Brook, Stony Brook, NY 11790 United States
AB: For a direct comparison with PREM, the density for a pyrolite lower mantle has been calculated using various PVT data sets available in literature. Care was taken to account the effects of iron, aluminum and other minor elements on the unit cell volumes of individual phases. It was found that the density calculated from the high pressure and temperature data of Funamori et al. (1994) could match PREM at 700km depth and 1900K within an uncertainty less than .5%, if the pressure were re-defined in terms of the MgO scale proposed by Speziale et al. (2001) and the gold scale by Shim et al. (2002). The mutual-consistency among laboratory data, the pyrolite model and PREM indicates that the lower mantle is likely of a pyrolite composition, and that the two new equations for MgO and gold should be used as an appropriate choice for defining the pressure scale. The one proposed for gold by Anderson et al. (1989), on the other hand, gives a pressure that is about 1.5GPa lower at 28 GPa and 1900K. The difference represents a correction on $\gamma$, the Gruneisen parameter that defines the thermal pressure. It may provide an explanation for discrepancy observed between the 660 km seismic discontinuity and the ringwoodite to perovskite and MgO phase boundary. An equation of state is proposed for the entire region of the lower mantle, in which PREM defines the principal reference adiabat, and $\gamma$, the Gruneisen parameter, defines both the temperature gradient and the thermal pressure with respect to the adiabat of PREM. For such an equation, $\gamma$ as a function of density (or pressure) was determined under two constraints. The first one is provided by the bulk sound velocity estimated along the room temperature isotherm from the pressure-density data for a pyrolite composition. The second one is a hypothetical Hugoniut constructed under a linear Us-Up relationship observed in shock wave experiments. At the lower mantle conditions, $\gamma$ was found close to be a constant, with a value higher than that estimated in previous studies. As a consequence, the temperature rise and the thermal expansion as a function of pressure along the adiabat defined by PREM should also be higher. The Anderson-Gruneisen parameter, $\delta_{s}$, has also been estimated. At the lower part of the lower mantle, it was found to be less than 1, which may explain the negative correlation between the lateral variations of the bulk sound and shear wave velocities observed in tomography studies.
DE: 3909 Elasticity and anelasticity
DE: 3919 Equations of state
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2004 AGU Fall Meeting