83-7 Comparative Petrologic Analysis of Potential Noritic Diogenites to Yamato Type B Diogenites

Session: Asteroid Observations, Return Missions, and Meteoritics: Interweaving Perspectives and Data

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The howardite, eucrite, and diogenite (HED) meteorite clan originates from 4Vesta, an asteroid located between Mars and Jupiter. Recent studies have shown that Vesta’s north pole has a distinctive composition similar to the Yamato Type B diogenites. This composition has further been linked to the Rheasilvia impact basin on Vesta as this noritic lithology is found at the antipode of the basin. This link increases the importance of studying this meteorite group to understand the formation of Vesta.

The Type B diogenites, found in Antarctica by the National Institute of Polar Research in Japan, are some of the only known HED meteorites with this lithology. Interestingly, few, if any, samples in the US Antarctic Meteorite Collection have been assigned this classification. In this study, we conducted electron microprobe analysis of four US Antarctic diogenite meteorites for comparison with Type B diogenites to determine if they should be reclassified as “noritic diogenites”. These samples were hand selected due to their Fe-rich orthopyroxene compositions and potentially higher plagioclase abundance.

Results show that the pyroxene compositions in all four samples correspond to Type B diogenites (Mg# 66-68). Two-pyroxene thermometry yields equilibration temperatures similar to Type B diogenites as well (~950 C). However, all four samples have low amounts of plagioclase (1-5 vol.%) as compared to most Type B diogenites (10-12 vol.%). It’s possible that the samples analyzed were not large enough for representative mineral modes, as thin section samples were only 1-2 cm. Alternatively, these samples could simply be representative of a lithology intermediate orthopyroxenitic and Yamato Type B diogenites. Future work studying these intermediate meteorites can be valuable to further our understanding of Vesta’s evolution.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9080

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