Study on deep structure and dynamics of the mantle by calorimetric measurements of high pressure silicates

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Main research results of this project are as follows.1. Heat capacity and enthalpy of MgSi0_3 perovskite were mesured, using the perovskite sample synthesized at very high pressure and high temperature. Based on the measured thermo dynamic properties, phase boundary of dissoication of Mg_2SiO_4 spinel to MgSiO_3 perovskite plas MgO was precisely determined. The slope of the boundry suggests that the upper mantle and lower mantle convect separatery but intermittant convection occurs between them. An adiabatic geotherm in the lower mantle and the temperature at the lowermost mantle were estimated, using the heat capacity of MgSiO_3 perovskite.2. Transition enthalpy of MgSiO_3 garnet was measured using the sampie synthesized at very high pressure and high temperature, and the phase equiliblium boundar were calculated. It eas suggetsed from the phase diagram that the garnet-perovskite transition which occurs in the descending lithoshere promotes the subduction.3. Effect of pressure was observed on the partition coefficients of Ni, Mn and Co between metallic iron and silicates at high pressure and hgih temparature. This result suggests that the pressure effect should be incoporated in geochemical model of the core-mantle separation.Enthalpy measurements of MgSio_4-Fe_2SiO_4 olivine solid solution showed that nonideality of the olivine solid solution was symmteric with to respect to composition and the nonideality parameter was detemined.5. Stability fields of hollandite solid solution in the system KAISi_3O_8-NaAISi_3O_8 and of a new hexagonal(Mg, Ca)AI_2O_4 phase were detemined at high pressure and high temparature.These aluminous phases may be stable in the transition zone and the lower mantle.