Noble gases, bulk chemistry, and petrography of olivine-rich achondrites Eagles Nest and LEW88763: Comparison to brachinites

Details Noble gases, bulk chemistry, and petrography of olivine-rich achondrites Eagles Nest and LEW88763: Comparison to brachinites Noble gases, bulk chemistry, and petrography of olivine-rich achondrites Eagles Nest and LEW88763: Comparison to brachinites

Jan 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998m%26ps...33...31s&link_type=abstract

Meteoritics & Planetary Science, vol. 33, no. 1, pages 31-48.

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Scientific paper

Eagles Nest and LEW88763 are olivine-rich achondrites which have been suggested to be related to Brachina and ALH84025. Both are ultramafic, although LEW88763 has about 10% plagioclase, which Eagles Nest lacks. Olivine in Eagles Nest (Fo68) is virtually identical in composition to that in Brachina (Fo68-70), and that in LEW88763 is only slightly different (Fo63-64). The meteorites' cosmic ray exposure ages differ from each other and from Brachina and ALH84025. Like Brachina, Eagles Nest has a substantial amount of radiogenic 129Xe and an apparent K-Ar age of less than 4.5 Ga. LEW88763, on the other hand, has no detectable radiogenic 129Xe, an apparent K-Ar age of about 4.5 Ga, and a substantial amount of trapped Xe. The chemical composition of LEW88763 is within a factor of two of chondritic for virtually every element analyzed, including siderophiles, suggesting that it was melted (or at least heated and recrystallized) in a closed system. Analyses of the chemical composition of Eagles Nest are hampered by extensive terrestrial weathering, but it appears to also be broadly chondritic, although it, like Brachina, is depleted in siderophiles. Our data suggest that Eagles Nest is genetically related to Brachina, but that LEW88763 is not, a conclusion consistent with the oxygen isotopic data of Clayton and Mayeda (1996).

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