The most primitive mesosiderite Northwest Africa 1878, subgroup 0

Abstract

All mesosiderites previously reported were subjected to thermal metamorphism and/or partial melting on the parent body. Therefore, their primordial features have been mostly lost. Here, we report detailed petrological and mineralogical features on a mesosiderite, Northwest Africa (NWA) 1878. This meteorite comprises silicate lithology and aggregates of small spheroidal Fe-Ni metal grains. Silicate lithology typically shows igneous texture without recrystallization features, and mainly consists of low-Ca pyroxene and plagioclase. Pyroxenes often show normal zoning. Exsolution lamella of augite is rarely noticed and very thin in width, compared with other mesosiderites. A few magnesian olivine grains are encountered without typical corona texture around them. They are not equilibrated with pyroxene on a large scale. Plagioclase shows a wide compositional range. These results show that NWA 1878 hardly experienced thermal metamorphism, distinguished from mesosiderites of subgroups 1-4. Therefore, we propose that this is classified as subgroup 0 mesosiderite. Nevertheless, NWA 1878 was locally subjected to secondary reactions, such as weak reduction of pyroxene and Fe-Mg diffusion between olivine and pyroxene, on the parent body.

Petrology and mineralogy of mesosiderite Northwest Africa 12949: Implications for geological history on its parent body

“…Distinct from olivine‐bearing ultramafic clasts in mesosiderites recently reported (e.g., Kimura et al., 2020; Wang et al., 2010), Clast I shows some unique reaction features and mineral assemblages. Orthopyroxenes occur either at the margin of olivine or along the cracks in the interior of olivine grains; troilite and chromite grains pervasively occur within these orthopyroxenes (Figure 2b).…”

“…The HED data are fromMittlefehldt (2015). The mesosiderites data are fromFloran et al (1978),Hewins (1979),Kimura et al (1991Kimura et al ( , 2020,Mittlefehldt et al (1998),Wang et al (2010), andKong et al (2008). (Color figure can be viewed at wileyonlinelibrary.com.…”

Insight Into Geological Evolution of the Mesosiderite Parent Body From Olivine Alteration and Merrillite Pb‐Pb Age in Dong Ujimqin Qi

“…Alternatively, the orthopyroxene clasts probably crystallized from a Ti‐poor igneous system, leading to similar Ti contents between orthopyroxene clasts and Opx‐I inherited from olivine. This explanation is supported by the fact that the Ti contents of igneous orthopyroxene clasts in the most primitive mesosiderites (subgroup 0) are lower than the detection limit of EPMA (Kimura et al., 2020).…”

“…Major elements of minerals in Dong Ujimqin Qi mesosiderite are publicly available from the Zenodo Repository (Chen, 2023). Data cited in Figures are found in the literature, including orthopyroxene compositions (Floran et al, 1978;Kimura et al, 1991Kimura et al, , 2020Lelarge et al, 2022) and REEs of phosphates (Ward et al, 2017). 41000000), National Key Research and Development Program of China (2021YFA0716100), the National Natural Science Foundation of China (41973060, 41973065, 42202260, and 42073060), Civil Aerospace pre-research projects (D020202 and D020302), and the Minor Planet Foundation of China.…”

“…Major elements of minerals in Dong Ujimqin Qi mesosiderite are publicly available from the Zenodo Repository (Chen, 2023). Data cited in Figures are found in the literature, including orthopyroxene compositions (Floran et al., 1978; Kimura et al., 1991, 2020; Lelarge et al., 2022) and REEs of phosphates (Ward et al., 2017).…”