L'Olivine dans les howardites: origine,et implications pour le corps parent de ces météorites achondritiques

Electron microprobe analyses have been performed on 300 olivine grains found in 11 howardites. The olivine compositions almost continuously range from Fa 8 to Fa 89 with two prominent populations at Fa 13 and Fa 30. The tail of the fayalite contents distribution may correspond to the succession of several small clusters of Fe-rich olivine grains. Most howardites have olivine populations in common that would result from the fragmentation of different rocks of the howardites parent body. The distribution of the olivine grains between several groups of different $\text{FeO}\text{MnO}$ ratios indicates olivine crystallization from distinct magmas. The chemical characteristics of the olivines of the pallasites, diogenites and mesosiderites are found among the olivines of the howardites and suggests a common parent body for these different types of meteorites. The differentiation model of the eucrites parent body proposed by Stolper (1977) is extended to the partial fusion of distinct assemblages silicates + metal which could proceed from recrystallizations, under different oxidation-reduction conditions, of a primordial chondritic material depleted in volatile elements.