Shock-induced thermal history of an EH3 chondrite, Asuka 10164

Shock-induced features are abundantly observed in meteorites. Especially, shock veins, including high-pressure minerals, characterize many kinds of heavily shocked meteorite. On the other hand, no high-pressure phases have been yet reported from enstatite chondrites. We studied a heavily shocked EH3 chondrite, Asuka 10164, containing a vein, which comprises fragments of fine-grained silicate and opaque minerals, and chondrules. In this vein, we found a silica polymorph, coesite. This is the first discovery of a high-pressure phase in enstatite chondrites. Other high-pressure polymorphs were not observed in the vein. The assemblages and chemical compositions of minerals, and the occurrence of coesite indicate that the vein was subjected to the high-pressure and temperature condition at about 3-10 GPa and 1000 degrees C. The host also experienced heating for a short time under lower temperature conditions, from similar to 700 to similar to 1000 degrees C, based on the opaque minerals typical of EH chondrites and textural features. Although the pressure condition of the vein in this chondrite is much lower than those in the other meteorites, our results suggest that all major meteorite groups contain high-pressure polymorphs. Heavy shock events commonly took place in the solar system.