Thermodynamic Properties of Upper Mantle Minerals : Establishment for the Geothermonetry and Geobarometry

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1.Least squares technique is applied to the estimation of the equilibration pressures and temperatures of ultramafic rocks by the use of olivie-orthopyroxene-garnet geothermometry and geobarometry. On-cratonic palaeogeotherms have rather moderate gradients of about 5-6゜C/km beneath Lesotho, Premier, Frank Smith and Siberia areas. Off-cratonic palaeogeotherms show extremely steep gradients of 10-14゜C/km for Namibia, Montana and Navojo. The geotherms deduced for the oceanic regions are very similar to those of Clark and Ringwood (1964).2.High pressure experiments are carried out at 50 kbar pressure under temperatures 900-1500゜C for the phase reations among olivine, orthopyroxene, clinopyroxene and garnet in the syste CaO-FeO-MgO- <Al_2O_3> - <SiO_2> in order to reveal the thermodynamic properties of clinopyroxene solid solution. The crystalline mixtures of fayalite ( <Fe_2> <SiO_4> ), enstatite (Mg <SiO_3> ), diopside (CaMg <Si_2> <O_6> ) and pyrope ( <Mg_3> <Al_2> <Si_3> <O_(12)> ) are employed to monitor the direction for the mineral reactions. Exchange reaction of <Fe^(2+)> and <Mg^(2+)> between clinopyroxene and garnet is suitable for the geothromonetry.3.The Melting experiments for the high-magnesian andesite of Yakushiyama, Goshikidai area are carried out under the dry and <H_2O> -oversaturated conditions. This andesite magma coexists with the olivine-orthopyroxene bearing ultramafic rock (harzburgite) in the upper mantle, of which physical conditions are 10-20 kbar and 1060-1230゜C