No abstract

Simultaneous ultrasonic elastic wave velocity and in situ synchrotron X-ray measurements on grossular garnet were carried out up to 17 GPa and 1 650 K. P-and S-wave velocities and bulk and shear modulus showed linear pressure and temperature dependence. These data yielded a pressure derivative of the bulk modulus of 4.42(7) and a shear modulus of 1.27(3), which are in good agreement with those of garnets with variable chemical compositions. Temperature dependence of the bulk modulus of grossular (-1.36×10 -2 GPa/K) is also similar to that of other garnets, while the temperature dependence of the shear modulus of grossular (-1.11×10 -2 GPa/K) is higher than those of magnesium end-member garnets and pyrolitic garnet.

Elastic wave velocities of synthetic polycrystalline Mg3Al2(SiO4)3 garnet have been successfully measured to 20 GPa and temperatures up to 1700 K by ultrasonic interferometry combined with energy-dispersive synchrotron x-ray diffraction in a Kawai-type multi-anvil apparatus. Compressional (Vp) and shear (Vs) wave velocities as well as the adiabatic bulk (Ks) and shear (G) moduli exhibit monotonic increase with increasing pressure and decrease with increasing temperature, respectively. Two-dimensional (P-T) linear fittings of the present data yield the following parameters: KS0 = 170.0(2) GPa, əKs/əP = 4.51(2), əKs/əT = −0.0170(1) GPa/K, G0 = 93.2(1) GPa, əG/əP = 1.51(2), and əG/əT = −0.0107(1) GPa/K, which is in good agreement with the earlier results by Brillouin scattering and/or ultrasonic measurements at relatively low P-T conditions. The observed linear pressure and temperature dependence in both Vp and Vs is in contrast to the non-linear behavior of Vp and Vs for majorite garnet with the pyrolite composition, in particular for Vs.

No abstract