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

Abstract

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.

Dense collection areas and terrestrial alteration of meteorites in the Atacama Desert

“…Pourkhorsandi et al. (2022) interpreted that the Sm‐Nd isotopic deviation and rare earth element (REE) abundances' modification of hot desert chondrites result from terrestrial alteration induced by the contamination by terrestrial fluids with soil interaction and the leaching of chondritic components such as Ca‐phosphates. However, both alteration processes should have only slightly affected the bulk oxygen isotopic composition of Atacama chondrites (based on the few reported O‐isotopic data in the Meteoritical Bulleting database, 2023), when we compare to the O‐isotopic shift reported in other areas worldwide (Bischoff et al., 2022; Greenwood et al., 2012).…”

“…The overall good preservation of Atacama chondrites is further attested by (i) the similar 16 O‐rich isotopic composition of Los Vientos 051 among the newly defined CL group (Metzler et al., 2021) and (ii) similar O‐isotopic compositions of olivine and pyroxene crystals in Sierra Gorda 009 and Grosvenor Mountains (GRO) 95551, coming from Atacama and Antarctica, respectively (Ivanova et al., 2020). However, in terms of isotopic compositions, highly weathered Antarctic meteorites still exhibit less variability compared to meteorites from hot deserts (Maeda et al., 2021; Pourkhorsandi et al., 2022).…”

“…This allows the preservation of the initial fall location that can help studying strewn fields (e.g., Gnos et al., 2009; Kring et al., 2001; Pedersen et al., 1992; Zeng et al., 2018) and the meteorite flux (Bland, 2001; Drouard et al., 2019). Nevertheless, several studies have provided evidence for the significant terrestrial alteration of hot desert meteorites in comparison with Antarctic meteorites (Lee & Bland, 2004; Maeda et al., 2021; Pourkhorsandi et al., 2022). This distinction has cast doubt on the consideration that hot desert meteorites are suitable samples for investigating pre‐terrestrial processes (Pourkhorsandi et al., 2017).…”

“…Numerous factors can influence the terrestrial weathering of meteorites: the time spent in the terrestrial environment (called terrestrial age); the composition of the soil of the recovery site; the long‐term meteorological conditions of the area; and the chondrite group, size, shape, and porosity (e.g., Al‐Kathiri et al., 2005; Ouknine et al., 2019; Pourkhorsandi et al., 2022; Stephant et al., 2018; Valenzuela, 2011). Although the weathering products of chondrites are distinct in hot and cold deserts, comparing the degree of weathering of a large set of chondrites is challenging due to different classification systems.…”