The Famenin fall and other ordinary chondrites intermediate between H and L groups

Hamed Pourkhorsandi (1, 2) , J. Gattacceca (1) , Pierre Rochette (1) , Thomas Smith (3) , Lydie Bonal (4) , Massimo D’orazio (5) , Bertrand Devouard (1) , Corinne Sonzogni (1) , Vinciane Debaille (2)

1 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
2 ULB - Université libre de Bruxelles
3 IGG - Institute of Geology and Geophysics [Beijing]
4 IPAG - Institut de Planétologie et d'Astrophysique de Grenoble
5 Dipartimento di Scienze della Terra [Pisa]

The Famenin meteorite fell around 08:30 a.m. local time (GMT+4.5) on June 27, 2015 on the roof of a house in Famenin, a town in NW Iran. A single 640 g stone was recovered, shattered into several pieces upon impact. The shape of the impact hole and the relative position of the recovered meteorites indicate a N-NW fall direction. Famenin is an ordinary chondrite (OC) with well-preserved chondrules of various types, (Fe,Ni) metal, troilite, phosphate, and chromite. The organic matter systematics and the olivine and low-Ca compositional distributions (percent mean deviations 18% and 31%, respectively) indicate it is a type 3.4/3.8 chondrite. Considering the average chemical compositions of olivine (Fa17.5±4.7) and low-Ca pyroxene (Fs16.8±7.5), average Co content of the kamacite (5.6 mg g−1), and Cu/Ni and Ga/Ni ratios, Famenin should be classified as an H chondrite. However, saturation magnetization is 26.0 Am2 kg−1, indicating a bulk metal content similar to L chondrites. Similarly, the whole-rock Ni and Co contents (13073 and 540 µg g−1, respectively), and average chondrule diameter (550 µm) are closer to typical values for L chondrites than H chondrites. The (Fe,Ni) metal modal abundance (5 vol%), magnetic susceptibility, and possibly whole-rock oxygen isotopic composition indicate intermediate properties between H and L chondrites. Noble gas composition and cosmic-ray exposure ages of Famenin and El Médano 195 (another intermediate OC) shows their gas-rich character and an older ejection age from their parent body than those for the majority of H and L chondrites. Famenin, together with similar intermediate OCs, increases the diversity of this meteorite clan and suggests the existence of a separate OC group with a composition broadly intermediate between H and L groups for which a different designation (HL) is proposed. OCs likely originate from more than three parent bodies (H, L, and LL) as traditionally proposed.

Mots clés: Fall; Intermediate chondrite; HL; ordinary chondrites; classification

Domaines: Planétologie

Hamed Pourkhorsandi, J. Gattacceca, Pierre Rochette, Thomas Smith, Lydie Bonal, et al.. The Famenin fall and other ordinary chondrites intermediate between H and L groups. Meteoritics and Planetary Science, 2022, ⟨10.1111/maps.13801⟩. ⟨hal-03620610⟩