THE EQUATIONS OF STATE OF FORSTERITE, WADSLEYITE, RINGWOODITE, AKIMOTOITE, MgSiO3–PEROVSKITE, AND POSTPEROVSKITE AND PHASE DIAGRAM FOR THE Mg2SiO4 SYSTEM AT PRESSURES OF UP TO 130 GPa
P.I. Dorogokupets1, A.M. Dymshits2,3, T.S. Sokolova1, B.S. Danilov1, K.D. Litasov2,3
1Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, ul. Lermontova 128, Irkutsk, 664033, Russia
2V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
3Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
Keywords: Equation of state, Gibbs energy, forsterite, wadsleyite, ringwoodite, MgSiO
-perovskite, akimotoite, MgSiO
-postperovskite, periclase, Helmholtz free energy
Abstract
The equations of state of forsterite, wadsleyite, ringwoodite, MgSiO
3-perovskite, akimotoite, and postperovskite are set up by joint analysis of experimentally measured isobaric heat capacity, bulk moduli, thermal expansion depending on temperature at ambient pressure, and volume at room and higher temperatures. Modified equations of state based on the Helmholtz free energy are used to construct a thermodynamic model. The derived equations of state permit calculation of all thermodynamic functions for the minerals depending on temperature and volume or temperature and pressure. A phase diagram of the system MgSiO
3-MgO is constructed based on the differences in the Gibbs energy calibrated using the referred experimental points. The seismic boundaries at depths of 410 and 520 km and in the zone D ″ are interpreted on the basis of the phase transitions. The global upper/lower mantle discontinuity at a depth of 660 km remains debatable; it is in poor agreement with experimental and computational data on the dissociation of ringwoodite to perovskite and periclase.
DOI: http://dx.doi.org/10.1016/j.rgg.2015.01.011
|
