Anatomy of an Allende coarse-grained inclusion

摘要: Inclusion 5241 is a petrographically complex, coarse-grained CAI from the Allende meteorite, containing core with two and chemically distinct units. The surrounded by melilite mantle similar to that described for Type B1 inclusions, which consists of large, millimetersized crystals. different units are (1) spinel-free islands consisting melilite, fassaite, minor anorthite (2) spinel-rich areas major fassaite reversely zoned melilite. In this unit, spinel occurs in densely packed belts surrounding islands. Mineral chemistries those areas: unzoned displays very narrow chemical variation (<10 mol %) within individual crystals, ranging between Ak_(52) Ak_(68) all They also contain considerable amounts Na-melilite molecule (as much as 2.7 %). In contrast, barren Na-melilite: composition varies Ak_(43) Ak_(62), lowest Ak-content zone decorated inclusions. Zoning crystals not continuous inclusions), but rhythmic outwards, Ak_(30) Ak_(35) near core/mantle boundary followed decrease value center (Ak_(25)). rises again reaches Ak_(28) at rim inclusion. Fassaite typically concentrically zoned, Ti-Al-rich cores Ti-Al-poor rims. concentration Ti^(3+) some appears be lower than spinelrich areas. Zoning nonsystematic Tio_2 variations (2–12wt%). Bulk compositions plot inside B field considerably below Fo-An-Ge plane because they deficient. outside close pyroxene-saturated (STOLPER, 1982). Textural relations mineral islands, areas, cannot explained gas solid condensation, simple stage crystallization refractory silicate liquid, or evaporative loss distillation, suggest series complex events including capture bodies liquid; may have formed liquid enveloped core.