UCL Discovery

Abstract

Recent experimental work has shown that the pressure dependence of the thermal expansion coefficient can be expressed as: ( α / α 0 ) = ( ρ / ρ 0 ( - δ T   ( 1 ) where δ_{T}, the Anderson‐Gruneisen parameter, is assumed to be independent of pressure, and for the materials studied has a value that lies between 4 and 6. Calculation of δ_{T} from seismic data, however, appears to suggest a contradictory value of between 2 and 3 for mantle‐forming phases. Using an atomistic model based on our previously successful many‐body interatomic potential set (THBl), we have performed calculations to obtain values of δ_{T} for four major mantle‐forming minerals. Our model results are in excellent agreement with experimental data, yielding values of between 4 and 6 for forsterite and MgO, and values in the same range for MgSiO_{3-}perovskite and γ‐Mg_{2}SiO_{4}. Moreover, the calculations confirm that δ_{T} is indeed constant with pressure up to the core‐mantle boundary. The apparent conflict between the values of δ_{T} predicted from seismic data and those obtained from experiment, and now from theory, is discussed.

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