Nitrogen isotopic compositions in three Antarctic and two non-Antarctic eucrites

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Nitrogen isotopic compositions were determined with stepped combustion method for three Antarctic eucrites (Allan Hills-76005,Yamato (Y)-792510 and -82066) and two non-Antarctic eucrites (Juvinas and Camel Donga). The abundances of indigenous nitrogen in these eucrites are from 0.05 to 1.3ppm, much lower than that in ordinary chondrites. The less abundance of nitrogen for eucrites is due to thermal events on the parent body. Isotopic ratios of the trapped nitrogen are also considered. Contribution of terrestrial nitrogen (δ^<15>N from 0‰ to +20‰) and cosmogenic nitrogen (δ^<15>N>+100‰) is significant in the case of eucrites at low temperature (<600℃) and high temperature (>1000℃) fractions, respectively. Hence, nitrogen released at medium temperature fractions is considered. The observed minimum δ^<15>N values released in medium temperature fractions of Y-792510 and Camel Donga are -54‰ and -18‰, respectively. The low δ^<15>N values cannot be explained by contribution of the terrestrial and cosmogenic components. This is strong evidence for existence of trapped components in eucrites which have ^<15>N/^<14>N ratios different from the atmospheric value. Since there may be some contribution of terrestrial or cosmogenic nitrogen even at medium temperature fractions, the minimum values observed in the present work should be considered as upper limits for the trapped components.
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