Abstract
A new assessment of the thermodynamic properties of the lower mantle yields a more secure value than hitherto for the adiabatic Anderson-Griineisen parameter at a nominal depth of 1771 km, ∂S=(∂In KS/ ∂lnρ)=1/αvKS(∂KS/∂T)P=2.4. The corresponding temperature dependence of rigidity is not well constrained but for the purpose of calculations is assumedd to be e=1/αVμ (∂μ/∂T)P=9.0. These values give the temperature dependences of seismic velocities (∂Inα/∂T)P= -2.4×10-5 K-1, (∂Inβ/∂T)P = -4.8×10-5 K-1. These temperature sensitivities are insufficient to explain reported lower mantle velocity anomalies without implausible temperature variations. Although temperature variations in the lower mantle must occur, tomographic observations do not provide direct evident for them, but are probably dominated by compositional variations. However, some correlation between composition and temperature may be expected, so that tomography may give still an indication of the pattern of the core-to-mantle heat flux.
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