Verification of presence of olivine-high pressure phase in the deep interior of meteorite parent body

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We investigated the possibility of phase transformation of olivine to ringwoodite during cooling at constant pressure in order to verify the presence of olivine high pressure phases in the deep interior of meteorite parent body. The study has been done by the following process. 1)Development of high pressure cell. 2)High pressure and temperature experiments of olivine using a Kawai-type high pressure apparatus. 3)Observation of microstructures of recovered samples. The results obtained by this research are :(1)Samples were first pressurized to 9 GPa, 10 GPa or 11 GPa at room temperature, then heated up to 1400℃ whose conditions were olivine stability field. The heating duration at 1400℃ were 2 hours. This heating treatment removed elastic and plastic strains generated in sample during the pressurization which enormously have influence on transformation.(2)After the heating at 1400℃, only temperatures were reduced to 700℃, 800℃ or 1000℃ in order to change the experimental conditions to olivine+ringwoodite stability field. And then, these conditions were kept for 2 and 5 hours. The observations of recovered samples indicate that olivines have not transformed to any high pressure polymorphs. The following two possibilities are considered as causes for such not-transformation. (a)Generated pressures reduced during decreasing of temperature, so that olivines were set in the it's stability field during whole experimental time. (b)Transformation rate from olivine to ringwoodite is very sluggish at 700℃, 800℃ or 1000℃, so that ringwoodite could not be detected.