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Published July 1977 | Published
Journal Article Open

Correlated O and Mg isotopic anomalies in Allende Inclusions: II. Magnesium


Mg in two Allende Ca-Al rich inclusions shows large isotopic, mass-dependent fractionation which enriched the heavier isotopes. After normalization, Mg in these inclusions shows negative δ^(26)Mg which appears to require the presence of nuclear effects in Mg distinct from ^(26)Al decay. The Mg mass fractionation is correlated with distinct but smaller fractionation effects for O reported by Clayton and Mayeda for the same inclusions (see companion paper). The observation of distinctive but uniform Mg isotopic composition in different phases within single Allende inclusions indicates that nuclear effects in O and Mg are not due to the entrapment of interstellar carrier grains as discrete entities, which are preserved as remnants, but are instead due to a homogenized mixture of components of extraordinary isotopic composition mixed with a component of ordinary solar system material and subjected to isotopic fractionation. The distinct O isotopic composition of different phases within a single inclusion is believed to be due to incomplete back-reaction of the higher temperature condensates with a cooler solar nebula of "normal" composition. The processes responsible for the O and Mg nuclear effects and the astrophysical site of their occurrence remain undefined.

Additional Information

© 1977 American Geophysical Union. Received April 15, 1977: accepted April 28, 1977. We thank H. Nagasawa for generously providing us materials from inclusion EKI-4-1. We thank D. Heymann for coming out of the trench where he was hiding from pre-solar grain dum-dums and supernovatic grenades to review this paper. This work was supported by NSF grant PHY 76-02724 and NASA grant NGL 05-002-188.

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