Lunar vesicular melt breccia (77135) was mineralogically compared with LL chondritic analog Yamato 790964 to elucidate impact melting processes. Microprobe analyses were made of pyroxenes, plagioclases, and olivines and of bulk compositions of the glasses which appear to be solidified from impact melts. Notable similarities between the lunar and chondritic melt breccias are (1) abundant vesicles, (2) similar pyroxene chemical zoning trends, (3) presence of variable amounts of clastic material, and (4) similar chemical compositions except for K and Na contents of the glass and mesostasis. Some constraints on the cooling history are estimated from Mg-Fe diffusion profiles in olivine and pyroxene. The burial depth of lunar sample 77135 during cooling was not large (0.2--100 m). For the chondrite the burial depth during cooling is probably smaller than that of the lunar analog. Even if the size of the chondrite parent body is small, it is probable that impact melts were produced and a layer of ejecta debris was produced which was sufficiently thick to homogenize Mg-Fe chemical zoning of olivines. |