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

Abstract

Ultrasonic interferometric measurements on polycrystalline Fe₂SiO₄ spinel were conducted simultaneously with synchrotron X-ray diffraction and X-ray imaging up to 6.5 GPa, 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: K _s0=204.5(7) GPa,=73.6(3) GPa, K′ _s =4.3(3), G′=1.2(1), (∂ K _s /∂ 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 (K _s ) increases slightly with increasing iron content, while the shear modulus (G), in contrast, shows a dramatic decrease. However, the pressure and temperature derivatives of K _s and G remain nearly constant from Mg₂SiO₄ to Fe₂SiO₄ spinel with average values of 4.2–4.4, 1.2–1.3,−0.024 GPa/K, and−0.016 GPa/K for K′ _s , G′, (∂ K _s /∂ 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: K _s =184.7+18.0 X _Fe, and G=118.7−41.5 X _Fe.

Keywords:

• ultrasonic interferometry
• Fe₂SiO₄ spinel
• elastic properties
• iron content

Acknowledgements

The authors thank Dr. Donald Lindsley for providing the fayalite sample powder. They also thank the editor and the reviewers who helped improve the manuscript. This project was supported by NSF grant to B. Li (EAR0635860). The experiment was conducted at X17B2 of NSLS, Brookhaven National Laboratory which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract no. DE-AC02-98CH10886 and by COMPRES, the Consortium for Materials Properties Research in Earth Sciences under NSF Cooperative Agreement EAR 06-49658, Mineral Physics Institute Publication No. 469.