Elasticity of diopside to 8 GPa and 1073 K and implications for the upper mantle

Simultaneous measurements of elastic wave velocities and density have been conducted on diopside by a combined ultrasonic interferometry and X-ray diffraction methods at pressure and temperature conditions relevant to the Earth's upper mantle. The current study not only yielded the first direct measurement of the shear modulus at high pressures, but also enabled a simultaneous determination of the bulk and shear properties and their pressure and temperature derivatives from the measured density and velocities. Finite strain analysis of the experimental data results in KS0 = 116.4(7) GPa, K′S0=4.9(1)K′S0=4.9(1), (∂KS/∂T)P = −0.012(1) GPa GPa, G′0=1.6(1)G′0=1.6(1) and (∂G/∂T)P = −0.011(1) GPa/K. With these results and the same finite strain equations, the P and S wave velocities of diopsidic mantle clinopyroxene were calculated along a 1600 K adiabatic geotherm. In comparison with other mantle minerals, the seismic velocities of diopsidic clinopyroxene at upper mantle depths are 1–3% higher than those of orthopyroxene, 1–2% and 6–8% lower than those of olivine and majoritic garnet, respectively.