Elasticity of an upper mantle clinopyroxene |
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| Authors: | M D Collins J M Brown |
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| Institution: | (1) Geophysics Program, University of Washington, Seattle, WA 98195 USA, Fax: +1(206)543-0489, e-mail: brown@geophys.washington.edu, US |
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| Abstract: | The ambient pressure elastic properties of a natural clinopyroxene (C2/c symmetry) from Kilbourne Hole, NM have been determined.
In terms of end-members, diopside (CaMgSi2O6), hedenbergite (CaFeSi2O6), jadeite (NaAlSi2O6), cosmochlor (NaCrSi2O6), and Mg-Tschermak (MgAl(AlSi)O6), its composition is Di72He9Jd3Cr3Ts12. The analytic density, based on chemistry and cell parameters is 3.327 (0.003) g/cm3. The elastic constants c11, c12, c13, c15, c22, c23, c25, c33, c35, c44, c46, c55, c66] are 273.8 (0.9), 83.5 (1.3), 80.0 (1.1), 9.0 (0.6), 183.6 (0.9), 59.9 (1.6), 9.5 (1.0), 229.5 (0.9), 48.1 (0.6), 76.5 (0.9),
8.4 (0.8), 73.0 (0.4), 81.6 (1.0)] GPa where uncertainties are reported at the 95% confidence level. The aggregate (mean of
Hashin-Strikman bounds) adiabatic bulk modulus is 117.2 (0.7) GPa, and the shear modulus is 72.2 (0.2) GPa. Although measured
moduli are broadly consistent with trends in elasticity versus atomic volume, deviations from the systematics would produce
significant (percent level) changes in calculated velocities for candidate mantle mineral assemblages. The compositional dependence
of elasticity for several clinopyroxenes is explored on the basis of just the Di+He and Jd+Ts mole fractions. The bulk modulus
lies within experimental uncertainties of the linear mixture of end-member properties while the shear modulus deviates by
3%.
Received: 29 September 1997 / Revised, accepted: 4 March 1998 |
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| Keywords: | Pyroxene Elasticity Monoclinic Systematics ISS |
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