Oxygen isotope exchange between refractory inclusion in allende and solar nebula Gas
A calcium-aluminum-rich inclusion (CAI) from the Allende meteorite was analyzed and found to contain melilite crystals with extreme oxygen-isotope compositions ( approximately 5 percent oxygen-16 enrichment relative to terrestrial oxygen-16). Some of the melilite is also anomalously enriched in oxygen-16 compared with oxygen isotopes measured in other CAIs. The oxygen isotopic variation measured among the minerals (melilite, spinel, and fassaite) indicates that crystallization of the CAI started from oxygen-16-rich materials that were probably liquid droplets in the solar nebula, and oxygen isotope exchange with the surrounding oxygen-16-poor nebular gas progressed through the crystallization of the CAI. Additional oxygen isotope exchange also occurred during subsequent reheating events in the solar nebula.
Yurimoto
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H. Yurimoto, Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Meguro, Tokyo 152-8551, Japan. M. Ito and H. Nagasawa, Department of Chemistry, Gakushuin University, Mejiro, Toshima, Tokyo 171-8588, Japan.
Ito
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Nagasawa
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