“…(2011) and in Demidova et al. (2014) with our results shows that the mineral chemistry and the texture of many of the clasts in Dhofar 1442 are very similar to clasts in NWA 11962. Despite the differences in bulk FeO and Th concentrations, this is the most interesting lunar meteorite in terms of a possible pairing relation to NWA 11962 (in addition to NWA 4472/4485).…”
Section: Discussionsupporting
confidence: 85%
“…Interestingly, Demidova et al. (2014) noted that the age variation of zircons in Dhofar 1442 is comparable to the age variation of zircons in NWA 4485. However, Ti‐rich glasses and olivine vitrophyric glass appear to be less common in Dhofar 1442 than in NWA 11962.…”
Northwest Africa (NWA) 11962 is a lunar regolith breccia composed of a wide range of different clasts. The lunar origin of this meteorite is confirmed by oxygen isotope analysis and the Fe/Mn ratio in pyroxene and olivine. In the present study, the clasts and the matrix of NWA 11962 are characterized by optical and electron microscopy along with electron microprobe analyses and micro‐Raman spectroscopy. The meteorite has a glassy impact melt matrix, which accounts for 35% of the surface area in the two thin sections examined, and which contains a very large variety of different lithic clasts, monomineralic clasts, and glass fragments. The presence of volcanic and impact‐related glass spherules led to the classification of this meteorite as a regolith breccia. Lithic clasts include numerous fragments of quartz monzogabbro and lunar felsite, which are quite rare lithologies in the lunar alkali suite. However, the most abundant components in the breccia are gabbroic clasts. The mineral chemistry of the pyroxenes in the gabbroic clasts and the chemistry of various types of glass fragments in the breccia indicate an origin of the regolith from an area with low‐Ti to high‐Ti mare basalt volcanism. In addition to the peculiar petrographic characteristics of NWA 11962, the possible pairing relationships with other lunar meteorites are discussed.
“…(2011) and in Demidova et al. (2014) with our results shows that the mineral chemistry and the texture of many of the clasts in Dhofar 1442 are very similar to clasts in NWA 11962. Despite the differences in bulk FeO and Th concentrations, this is the most interesting lunar meteorite in terms of a possible pairing relation to NWA 11962 (in addition to NWA 4472/4485).…”
Section: Discussionsupporting
confidence: 85%
“…Interestingly, Demidova et al. (2014) noted that the age variation of zircons in Dhofar 1442 is comparable to the age variation of zircons in NWA 4485. However, Ti‐rich glasses and olivine vitrophyric glass appear to be less common in Dhofar 1442 than in NWA 11962.…”
Northwest Africa (NWA) 11962 is a lunar regolith breccia composed of a wide range of different clasts. The lunar origin of this meteorite is confirmed by oxygen isotope analysis and the Fe/Mn ratio in pyroxene and olivine. In the present study, the clasts and the matrix of NWA 11962 are characterized by optical and electron microscopy along with electron microprobe analyses and micro‐Raman spectroscopy. The meteorite has a glassy impact melt matrix, which accounts for 35% of the surface area in the two thin sections examined, and which contains a very large variety of different lithic clasts, monomineralic clasts, and glass fragments. The presence of volcanic and impact‐related glass spherules led to the classification of this meteorite as a regolith breccia. Lithic clasts include numerous fragments of quartz monzogabbro and lunar felsite, which are quite rare lithologies in the lunar alkali suite. However, the most abundant components in the breccia are gabbroic clasts. The mineral chemistry of the pyroxenes in the gabbroic clasts and the chemistry of various types of glass fragments in the breccia indicate an origin of the regolith from an area with low‐Ti to high‐Ti mare basalt volcanism. In addition to the peculiar petrographic characteristics of NWA 11962, the possible pairing relationships with other lunar meteorites are discussed.
“…4Time-integrated Th/U as a function of that measured for lunar zircons. Corresponding data are presented in Supplementary Data 3 and come from Compston et al 60 , Demidova et al 61 , Leont’eva et al 62 , and Nemchin et al 63–65 . Note the general good agreement between measured and time-integrated Th/U, as well as the fact that Th/U range between 0.2 and 1, which is identical to terrestrial igneous zircons 20 Fig.…”
Several lines of evidence support the presence of liquid water on Mars at different times. Among those, hydrated minerals testify to past aqueous weathering processes that can be precisely studied in Martian meteorites such as NWA 7533/7034. Bringing constraints on the timing of weathering of the Martian crust would help understand its evolution, the availability of liquid water, and the habitability of Mars. Here we present a new method based on U–Th–Pb isotope systems to assess if zircon crystals underwent low-temperature aqueous alteration, such as exemplified by Hadean-aged detrital crystals from Western Australia. Data for NWA 7533 zircons show evidence for aqueous alteration and modeling of U–Th–Pb isotope system evolution indicates that the latest alteration event occurred during the late Amazonian (227–56 Ma). This finding largely expands the time duration over which liquid water was available near the Martian surface, thereby suggesting that Mars might still be habitable.
Apollo 16 soil-like regolith breccia 65745,7 contains two zircon-bearing clasts. One of these clasts is a thermally annealed silica-rich rock, which mineralogically has affinities with the High Alkali Suite (Clast 1), and yields zircon dates ranging from 4.08 to 3.38 Ga. The other clast is a KREEP-rich impact melt breccia (Clast 2) and yields zircon dates ranging from 3.97 to 3.91 Ga. The crystalline cores of both grains, which yield dates of
ca
3.9 Ga, have undergone shock pressure modification at less than 20 GPa. We interpret that the U-Pb chronometer in these zircon grains has been partially reset by the Imbrium basin-forming event when the clasts were incorporated into the Cayley Plains ejecta blanket deposit. The zircon grains in Clast 1 have been partially decomposed, resulting in a breakdown polymineralic texture, with elevated U, Pb and Th abundances compared with those in the crystalline zircon. These decomposed areas exhibit younger dates around 3.4 Ga, suggesting a secondary high-pressure, high-temperature event, probably caused by an impact in the local Apollo 16 highlands area.
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