HR: 16:15h
AN: DI44A-02    [Abstracts]
TI: Thermodynamic Properties of the Magnesium-Olivine-Pyroxene System Derived From a Lattice Vibrational Technique
AU: * Jacobs, M H
EM: jacobs@geo.uu.nl
AF: Dept. Theoretical Geophysics, Faculty of Geosciences, Utrecht University, Budapestlaan 4, Utrecht, NL-3584CD, Netherlands
AU: van den Berg, A P
EM: Berg@geo.uu.nl
AF: Dept. Theoretical Geophysics, Faculty of Geosciences, Utrecht University, Budapestlaan 4, Utrecht, NL-3584CD, Netherlands
AU: de Jong, B H
EM: bernard@geo.uu.nl
AF: Petrology Group, Faculty of Geosciences, Utrecht University, Budapestlaan 4, Utrecht, NL- 3584CD, Netherlands
AB: We are currently constructing a thermodynamic database providing phase diagrams, thermophysical and thermochemical properties for materials with a geophysical relevance, applicable in the pressure and temperature regime of the Earth's mantle. The computational technique is based on Kieffer's (1979) approach to model the vibrational density of states of a substance, a key property to derive the Helmholtz energy. The developed thermodynamic framework, which allows the calculation of Vp and Vs sound wave velocities, uses model-input properties related to Raman and infrared spectroscopic data. It puts tighter constraints on thermodynamic properties compared to methods based on polynomial parameterizations of thermal expansivity, heat capacity and isothermal bulk modulus. Jacobs & de Jong (2005, 2007) showed that this framework discriminates, based on internal consistency, between the quality of disparate sets of experimental thermochemical, thermophysical and phase diagram data. The present work focuses on the application of vibrational modeling to the magnesium-olivine-pyroxene system, a system relevant to Earth's mantle. We show how our approach is used to point to inconsistencies in experimental datasets. Pressure calibration problems affecting the derivation of phase diagrams are discussed. The results, presented here, were used in a numerical model of convection in the Earth's mantle to reveal, effects of phase transitions on the degree of layering, mineral distribution and sound wave velocities in the transition zone, around 660 km depth in the Earth. References Kieffer S.W. (1979), Rev. Geophys. Space Physics, 17, 35-59. Jacobs M.H.G. and B.H.W.S. de Jong (2005), Phys. Chem. Minerals, 32, 614-626. Jacobs M.H.G., and de Jong B.H.W.S. (2007), Geochim. Cosmochim. Acta, 71, 3630-3655.
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3919 Equations of state
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting