Compressional and shear wave velocities of Fe2SiO4 spinel at high pressure and high temperature

Ultrasonic interferometric measurements on polycrystalline Fe2SiO4 spinel were conducted simultaneously with synchrotron X-ray diffraction and X-ray imaging up to 6.5GPa, 1073 K. The compressional and shear wave velocity data and the volume data were fitted to the third-order finite strain equations to derive the bulk and shear modulus and their pressure and temperature derivatives. The fitting results are as follows: Ks0=204.5(7)GPa,=73.6(3)GPa, K's=4.3(3), G'=1.2(1), ( Ks/ T)p=-0.027(2)GPa/K, and ( G/ T)p=-0.017(1)GPa/K. Comparison of our current results with previous data on (Mg,Fe)2SiO4 spinel with different compositions suggests that the bulk modulus (Ks) increases slightly with increasing iron content, while the shear modulus (G), in contrast, shows a dramatic decrease. However, the pressure and temperature derivatives of Ks and G remain nearly constant from Mg2SiO4 to Fe2SiO4 spinel with average values of 4.2-4.4, 1.2-1.3,-0.024GPa/K, and-0.016GPa/K for K's, G', ( Ks/ T)p, and ( G/ T)p, respectively. The proposed version of equations to describe the effects of iron on the elastic moduli of ringwoodite are: Ks=184.7+18.0 XFe, and G=118.7-41.5 X Fe.