Petrology of chondrules, inclusions and isolated olivine grains in ALH-77307 (CO3) chondrite

A petrological study has been conducted on ALH-77307 (CO3) chondrite. Chondrules are classified into magnesian type and iron-rich type. The magnesian chondrules contain olivine and clinoenstatite with a small amount of groundmass, whereas the iron-rich chondrules contain only olivine as phenocrysts in the groundmass. Inclusions show gradual changes in crystallinity, grain size of constituents, texture and shape. The difference among the inclusions is considered to be due to the difference of heating temperature of the precursor finegrained materials. Intensive heating of the inclusions might have formed the magnesian chondrules. Isolated olivine grains are also classified into magnesian and iron-rich types, which are thought to have been derived from the magnesian and iron-rich chondrules, respectively. Genetical relations of chondrules, inclusions and isolated olivine grains are discussed by the process of condensation, successive heating, break up, and accreation.