Dhofar 081: A new lunar highland meteorite

Abstract

The lunar meteorite Dhofar 081, found as a single fragment of 174 g in the Dhofar region of Oman, is a shocked feldspathic fragmental highland breccia dominated by anorthosite-rich lithic and mineral clasts embedded into a fine-grained mostly shock melted clastic matrix. Major mineral phases in the bulk rock are Ca-rich plagioclase (An96.5-99.5), pyroxene (Fs21.9-46.2 Wo3.0-41.4), and olivine (Fa29.3-47.8); accessory phases include Fe-Ni metal, ilmenite, and Ti-Cr-rich spinel. Dhofar 081 contains subordinate crystalline fragments of large anorthosites, intersertal impact-melt rocks, microporphyritic impact-melt breccias, dark fine-grained impact-melt breccias, large cataclastic feldspars, and irregularly shaped brown glass clasts. Mafic components are rare and no genuine regolith components were found in the sections studied. Minerals in Dhofar 081 show homogeneously distributed shock features: intergranular recrystallization, strong fracturing and mosaicism in feldspar as well as a high density of mostly irregular fractures in pyroxene and olivine. Localized impact melting caused by one or several impacts led to a strong lithification. Based on these effects an equilibration shock pressure of about 15-20 GPa is estimated for the strongest shock event in Dhofar 081. Devitrification of the "glassy" material in the rock indicates thermal annealing after shock melting suggesting that the 15-20 GPa shock event predated the ejection event. According to the concentrations of implanted solar noble gases Dhofar 081 represents a polymict clastic breccia deposit with possibly a minor regolith component. A similar noble gas record of Dhofar 081 and MacAlpine Hills 88104/05 suggests the possibility of a source crater pairing of both meteorites. As indicated by noble gas measurements pairing of Dhofar 081 with the other lunar meteorites found in Oman, Dhofar 025 and Dhofar 026, is unlikely.