THERMAL-EXPANSION OF MANTLE MINERALS AT HIGH-PRESSURES - A THEORETICAL-STUDY

Recent experimental work has shown that the pressure dependence of the thermal expansion coefficient can be expressed as:   where δT, 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 δT 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 δT 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 MgSiO3−perovskite and γ‐Mg2SiO4. Moreover, the calculations confirm that δT is indeed constant with pressure up to the core‐mantle boundary. The apparent conflict between the values of δT predicted from seismic data and those obtained from experiment, and now from theory, is discussed. Copyright 1990 by the American Geophysical Union.