Accurate and rapid measurements of thermodynamic properties of minerals by microcalorimetric method.

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1. Heat capacities of high-pressure silicate minerals were measured by the differencial scanning calorimeter which was installed by the grant-in-aid for scientific research. The data processing system using the personal computor was made for rapid and accurate calculation of the heat capacity measured by the differencial scanning calorimeter. Garnet solid solutions containing pyroxene components are stable in the pressure-temperature conditions in the mantle transition zone. Heat capacities of the garnet solid solutions in the system <Mg_4> <Si_4> <O_(12)> - <Mg_3> <Al_2> <Si_3> <O_(12)> , which represent the garnets in the transition zone, were measured by the present heat capacity measurement system. It was observed that heat capacity of the garnet solid solution at each temperature changed very little with increasing <Mg_4> <Si_4> <O_(12)> component. The Gruneisen parameter and Debye temperature of the garnet solid solutions were estimated from the heat capacity data.2. Enthalpies of silicates and germanates stable at high pressures were measured. Enthalpies of transition of the silicates and germanates were obtained for the following systems:(1) rhodonite-clinopyroxene-garnet transitions in MnSi <O_3> , (2) wollastonite-garnet-perovskite transitions in CaGe <O_3> , (3) pyroxenoid-garnet-ilmenite-perovskite transitions in CdGe <O_3> , (4) pyroxene-garnet transition in the system <Mg_4> <Si_4> <O_(12)> - <Mg_3> <Al_2> <Si_3> <O_(12)> .Phase boundaries for the above transitions were calculated from the measured enthalpies.They were almost consistent with the boundaries determined by the phase equilibrium experiments. It was established that the pyroxene(or pyroxenoid)- garnet transitions have generally gentle positive dP/dT slopes, while the ilmenite (or garnet)-perovskite transitions have negative slopes.