Original paper

The pressure dependence of the elastic moduli of single-crystal orthopyroxene (Mg0.8Fe0.2)SiO3

Webb, Sharon L.; Jackson, Ian

European Journal of Mineralogy Volume 5 Number 6 (1993), p. 1111 - 1120

21 references

published: Dec 1, 1993
manuscript accepted: Aug 16, 1993
manuscript received: Mar 18, 1993

DOI: 10.1127/ejm/5/6/1111

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Abstract The adiabatic pressure dependences of the nine independent elastic moduli of orthopyroxene have been measured by improved techniques of ultrasonic interferometry over a 3 GPa range of hydrostatic pressure at room temperature. This large pressure range together with the accuracy of the phase comparison ultrasonic technique allows the determination of both the first- and second-pressure derivatives of the elastic moduli of orthopyroxene. The calculated zero-pressure bulk (K0) and shear (G0) moduli of an ideal isotropic homogeneous polycrystal of the present composition over the 0-3 GPa pressure range are K0 = 109.4±0.5 GPa K0' = 10.8+0.8 K0" = -1.6±0.2 GPa-1 G0 = 75.2±0.4 GPa G0' = 2.06±0.07 G0" = -0.12±0.0 GPa-1 where the errors indicate the range between the greatest lower-bound and the least upper-bound of the Hashin- Shtrikman values; the modulus as a function of pressure is M(P) = Mo + Mo P + 0.5 M0 P2 . The observed pressure dependences of the moduli are in general accord with the earlier study of Frisillo & Barsch (1972). In particular the pressure derivatives (at zero pressure) of the compressional and off-diagonal moduli (and hence of the bulk modulus) are anomalously large in comparison with other upper mantle minerals (typically 4


elastic moduliultrasonicsorthopyroxenepressure-dependence