Elasticity of polycrystalline MgSiO3-orthoenstatite to 1373K

Orthopyroxene is an important mineralogical constituent of petrological models of the Earth's upper mantle. To construct the mineralogical models for Earth's mantle, the pressure and temperature derivatives of the bulk and shear moduli are essential. The elasticity data for orthoenstatite (OEN) are, mainly, available at high pressure conditions (Flesch et al., 1998; Angel and Jackson, 2002; Kung et al. 2004). Some selected elastic constants (Cij) of the OEN phase were measured up to high temperature, room pressure by Jackson et al. (2004), however, they are insufficient to calculate the bulk elasticity properties for the aggregates. In this study, P and S wave sound velocities have been measured on dense isotropic polycrystalline MgSiO3-OEN in an internally heated gas-medium high-pressure apparatus. Two different runs were carried out up to 973K and 1373K at 300 MPa. Both P and S wave velocities from two runs decrease linearly as function of temperature and show highly agreement below 973K. The temperature derivatives of velocities above 1100K are very different from those below 973K. We speculated that the changes of temperature dependence at high temperature are related to the velocity softening" observed in MgSiO3 due to the phase transition (Jackson et al.,2004). We will present our new measurements in the meeting. Ref: Flesch et al. (1998) Am. Miner. 83(5-6), 444-450. Angel and Jackson (2002) Am. Mineral. 87(4), 558-561. Kung et al. (2004) Phys. Earth Planet. Inter., 147(1), 27-44. Jackson et al. (2004) Am. Mineral. 89(1), 239-244.