Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measure the mineralogy, bulk chemical and isotopic compositions of Ryugu samples. They are mainly composed of materials similar to carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37 ± 10°C, 5.2 − 0.8 + 0.7 (Stat.) − 2.1 + 1.6 (Syst.) million years after formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles the Sun’s photosphere than other natural samples do.

Abstract-Northwest Africa (NWA) 2977 is an olivine-gabbro lunar meteorite that has a distinctly different petrographic texture from other lunar basalts. We studied this rock with a series of in situ analytical methods. NWA 2977 consists mainly of olivine and pyroxene with minor plagioclase. It shows evidence of intense shock metamorphism, locally as high as shock-stage S6. Olivine adjacent to a melt vein has been partially transformed into ringwoodite and Al,Ti-rich chromite grains have partially transformed into their highpressure polymorph (possibly CaTi 2 O 4 -structure). Olivine in NWA 2977 contains two types of lithic inclusions. One type is present as Si,Al-rich melt inclusions that are composed of glass and, in most cases, dendritic pyroxene. The other type is mafic and composed of relatively coarse-grained augite with accessory chromite, RE-merrillite, and baddeleyite. Two Si,Al-rich melt inclusions are heavy rare earth elements (REE) enriched, whereas the mafic inclusion has high REE concentrations and a KREEP-like pattern. The mafic inclusion could be a relict fragment captured during the ascent of the parent magma of NWA 2977, whereas the Si,Al-rich inclusions may represent the original NWA 2977 melt. The calculated whole-rock composition has a KREEP-like REE pattern, suggesting that NWA 2977 has an affinity to KREEP rocks. Baddeleyite has recorded a young crystallization age of 3123 ± 7 Ma (2r), which is consistent with results from previous whole-rock and mineral Sm-Nd and Rb-Sr studies. The petrography, mineralogy, trace element geochemistry, and young crystallization age of NWA 2977 support the possibility of pairing between NWA 2977 and the olivine-gabbro portion of NWA 773.

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We report on the petrography and mineralogy of three types of silicate veinlets in the brecciated eucrite Northwest Africa (NWA) 1109. These include Fe‐rich olivine, Mg‐rich olivine, and pyroxene veinlets. The Fe‐rich olivine veinlets mainly infill fractures in pyroxene and also occur along grain boundaries between pyroxene and plagioclase crystals, in both nonequilibrated and equilibrated lithic clasts. The host pyroxene of Fe‐rich olivine veinlets shows large chemical variations between and within grains. The Fe‐rich olivine veinlets also contain fine‐grained Fe3+‐bearing chromite, highly calcic plagioclase, merrillite, apatite, and troilite. Based on texture and mineral chemistry, we argue that the formation of Fe‐rich olivine was related to fluid deposition at relatively high temperatures. However, the source of Fe‐rich olivine in the veinlets remains unclear. Magnesium‐rich olivine veinlets were found in three diogenitic lithic clasts. In one of these, the Mg‐rich olivine veinlets only occur in one of the fine‐grained interstitial regions and extend into fractures within surrounding coarse‐grained orthopyroxene. Based on the texture of the interstitial materials, we suggest that the Mg‐rich olivine veinlets formed by shock‐induced localized melting and recrystallization. Pyroxene veinlets were only observed in one clast where they infill fractures within large plagioclase grains and are associated with fine‐grained pyroxene surrounding coarse‐grained pyroxene. The large chemical variations in pyroxene and the fracture‐filling texture indicate that the pyroxene veinlets might also have formed by shock‐induced localized melting and rapid crystallization. Our study demonstrates that silicate veinlets formed by a range of different surface processes on the surface of Vesta.