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

Akira Yamaguchi , Makoto Kimura , Jean-Alix Barrat (1) , Richard Greenwood

1 LGO - Laboratoire Géosciences Océan

We performed a petrologic, geochemical, and oxygen isotopic study of the lowest FeO ordinary chondrite (OC), 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 (Fa_{11.17 ± 0.48 (1σ)}) and low-Ca pyroxene (Fs_{11.07 ± 0.98 (1σ)}Wo_{0.90 ± 0.71(1σ)}) is significantly more magnesian than those of typical H chondrites (Fa_16.0-20, Fs_14.5-18.0), as well as other known low-FeO OCs (Fa_12.8-16.7; Fs_13-16). 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.

Domaines: Planète et Univers [physics]

Akira Yamaguchi, Makoto Kimura, Jean-Alix Barrat, Richard Greenwood. Compositional diversity of ordinary chondrites inferred from petrology, bulk chemical, and oxygen isotopic compositions of the lowest FeO ordinary chondrite, Yamato 982717. Meteoritics & Planetary Science, 2019, 54, pp.1919-1929. ⟨10.1111/maps.13351⟩. ⟨insu-03685655⟩