PHASE RELATION AND PHYSICAL PROPERTIES OF AN AL-DEPLETED KOMATIITE TO 23 GPA

Abstract

Knowledge of the mineralogical constituents of the Earth's mantle depends heavily on high-P experiments of pyrolite composition. In order to understand the planetary interior better, phase relations and mineral physics properties of compositions other than pyrolite may also be important. High-P and high-T experiments were conducted on an Al-depleted komatiite which can be regarded as a kind of piclogite composition. Fourteen experiments were carried out along a model geotherm between 5 and 23 GPa and 1100 and 1600°C with a multi-anvil apparatus. Analyses of quenched run products showed that, in the studied komatiite, the fractions of olivine and its high-P polymorphs (wadsleyite and ringwoodite) are 40-50 vol%, pyroxene-garnet phase transition occurs at 13-17 GPa (while the respective values for pyrolite are ~60 vol% and 12-15 GPa). The density and seismic velocity profiles of komatiite mantle were calculated using thermoelastic parameters of related minerals, and they showed quite good agreements with those of seismic observations around the transition zone as well as those for pyrolite.