Shock metamorphic history of primitive meteorites: experimental approach

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(1) Heating effects of an experimentally shocked hydrated chondrite: Comparison with micrometeorites: Our transmission electron microscope study of a hydrated porous meteorite experimentally shocked at pressures of 10-49 GPa shows that its mineralogy and texture are similar to those of micrometeorites. The results suggest that micrometeorites are likely to have gone through shock heating processes that took place during asteroidal impacts before atmospheric entry.(2) Microinclusion-rich vesicular olivine in CK4 chondrites: A product of shock at high temperature: Our transmission electron microscope study reveals that a CK4 chondrite contains a high abundance of unusual olivine that contains high densities of submicrometer-size vesicles and inclusions of a variety of minerals. The results suggest that the vesicular olivine was formed by crystallization of melts that were produced by shock at a high temperature.(3) Hydrothermal alteration experiments of enstatite: Implications for aqueous alteration in chondrites: Hydrothermal alteration experiments of enstatite were carried out at pH 0-14, at 100-300℃, and for 24-336 hours in order to provide constraints on aqueous alteration conditions of hydrated meteorites. The results indicate that alteration of enstatite is strongly dependent on pH. The results therefore suggest that the differences in phyllosilicate mineralogy among the different types of chondrite mainly resulted from different pH conditions of aqueous solutions.(4) Mineralogical investigation of Comet Wild 2 samples returned by Stardust: Our transmission electron microscope study of comet Wild 2 samples shows that they consist mainly of crystalline silicates and minor amounts of Fe-Ni sulfide and metal, and their mineralogical characteristics are similar to those of the carbonaceous chondrites. One olivine grain has a texture suggesting that the Wild2 particles experienced hypervelocity impacts before capture.