SHOCK-PRODUCED VAPOR-GROWN CRYSTALS IN THE YANZHUANG METEORITE

Vapor-grown crystals intimately related to shock metamorphism of meteo rites were found in the Yanzhuang (H6) chondrite which had been heavil y impacted in the space. These crystals include: (i) subhedral low-Ca pyroxene occurring on the wall of the pores within a silicate melt poc ket that experienced a shock temperature higher than 1500 degrees C, ( ii)Fe-Ni needle-whiskers (taenite) occurring in the cracks in the part ially melted chondritic facies that experienced a shock temperature of 850-1300 degrees C, (iii) troilite with abundant microholes occurring in the cracks in the brecciated facies and the lightly deformed chond ritic facies that experienced a shock temperature lower than 850 degre es C. The occurrence and mineralogical features of vapor-grown crystal s show that vaporization of minerals could be produced in heavily impa cted meteorites and that a small amount of crystals could be deposited in situ from vapor phases.