Compositional diversity of ordinary chondrites inferred from petrology, bulk chemical and oxygen isotopic compositions of the lowest FeO ordinary chondrite, Yamato 982717

Yamaguchi, Akira; Kimura, Makoto; Barrat, Jean-Alix and Greenwood, Richard (2019). Compositional diversity of ordinary chondrites inferred from petrology, bulk chemical and oxygen isotopic compositions of the lowest FeO ordinary chondrite, Yamato 982717. Meteoritics and Planetary Science, 54(9) pp. 1919–1929.

DOI: https://doi.org/10.1111/maps.13351

Abstract

We performed a petrologic, geochemical, and oxygen isotopic study of the lowest FeO ordinary chondrite, Yamato (Y) 982717. Y 982717 shows a chondritic texture composed of chondrules and chondrule fragments, and mineral fragments set in a finer-grained, clastic matrix, similar to H4 chondrites. The composition of olivine (Fa11.17 ± 0.48 (1σ)) and low-Ca pyroxene (Fs11.07 ± 0.98 (1σ)Wo0.90 ± 0.71(1σ)) are significantly more magnesian than those of typical H chondrites (Fa16.0-20, Fs14.5-18.0), as well as other known low-FeO OCs (Fa12.8-16.7; Fs13-16). However, the bulk chemical composition of Y 982717, in particular lithophile and moderately volatile elements, is within the range of OCs. The bulk siderophile element composition (Ni, Co) is within the range of H chondrites and distinguishable from L chondrites. The O-isotopic composition is also within the range of H chondrites. The lack of reduction textures indicates that the low olivine Fa content and low-Ca pyroxene Fs content are characteristics of the precursor materials, rather than the result of reduction during thermal metamorphism. We suggest that the H chondrites are more compositionally diverse than has been previously recognized.

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