干旱区生态环境知识资源中心

The 14 lunar meteorites identified thus far were found in Antarctica, the Sahara desert, and Australia. The study of the isotopic composition and concentrations of noble gases in them provides valuable information that makes it possible to determine the retention time of gases in these meteorites, the duration of their irradiation by cosmic rays both at the moon’s surface and in interplanetary space, and the residence time of the meteorites on earth. Our research was devoted to two lunar meteorites recently found in Oman: Dhofar 025 and Dhofar 026 [ I]. The Dhofar 025 meteorite is a brownish gray fragment 751 g in mass, found on March 5, 2000, near Dhofar (18degrees24.2’ N, 54degrees09.1’ E) and bearing no fused crust. The meteorite consists of regolith breccia rich in detrital fragments. Numerous monomineralic fragments and debris of feldspathic rocks are submerged in a glass-rich matrix with numerous schlieren and bubbles. The rock-forming minerals are plagioclase (An(95-96)), pyroxene (En(74-84), Wo(3-6), Fe/Mn = 50-70 at), and olivine (Fo(70-78), Fe/Mn = 91-97 at). The accessory minerals are high-Ti aluminochromite, ilmenite, silica phases, troilite, and metallic FeNi. The meteoritic material is characterized by a clearly pronounced Eu anomaly (Sm/Eu = 1.95) and bears only slight traces of terrestrial weathering. The Dhofar 026 meteorite, found on March 6, 2000, near Dhofar 025 (18degrees13.6’N, 54degrees06.7’ E), is a rounded brownish gray stone 148 g in mass, without a fused crust. Dhofar 026 is made up of anorthosite breccia with relatively scarce fragments of minerals and anorthositic rocks, which are submerged in a fully devitrified fine-grained matrix. The rock contains bubbles, spherical chondrulelike inclusions, and rare melt veins. The rock-forrning minerals are plagioclase Anq(96-98)), olivine (Fo(61-79), Fe/Mn = 80-120 at), low-Ca pyroxene (Wo(8-20), En(53-63), 0.13-0.84 wt % TiO2 Fe/Mn = 40-60 at), and high-Ca pyroxene (Wo(27-33), En(43-50) (TiO2 1.1-3.5 wt % TiO2 Fe/Mn = 40-50 at). The accessories are silica, ilmenite (7 wt % MgO), troilite, and an FeNi metallic phase. The Eu anomaly is clearly pronounced (Sm/Eu = 1.04), and the traces of terrestrial weathering are weak. The texture and composition of this meteorite are significantly different from those of Dhofar 025, but it cannot be ruled out that both meteorites were ejected from the moon during the same impact event. The goals of his research were formulated as follows: (1) determine the characteristics ofthe noble gases to confirm the lunar provenance of these meteorites, (2) examine the regularities in the isotopic composition and concentrations of the noble gases captured in the Dhofar 025 and Dhofar 026 meteorites, (3) estimate the exposure age of these meteorites, and (4) use the isotopic features of the noble gases to explore the possibility of the independent ejection of Dhofar 025 and Dhofar 026 from the moon.