Petrography and Mineralogy of Dhofar 1428 Lunar Highland Regolith Breccia

Introduction: Dhofar 1428 is a lunar feldspathic breccia found in 2006. Bunch et al. [1] briefly described mineral chemistry of Dhofar 1428. Korotev and Zeigler [2] analyzed its bulk FeO and Sm compositions. Here, we report such detailed data for Dhofar 1428. Results and Discussion: Dhofar 1428 has a distinct breccia texture with numerous fragments of rock, mineral, and glass all welded by a glassy matrix. This matrix shows a schlieren texture and contains numerous small rounded vesicles, implying that Dhofar 1428 is a regolith breccia. Feldspathic lithic clasts are the dominant clast type, and ma-fic lithic clasts also exist. These lithic clasts range from troctolite to spinel troctolite, to anorthositic gabbro, and to anorthosite. Most lithic clasts show a fine-grain granulitic texture. A few lith-ic clasts have a subophitic texture and are relatively coarse-grained. Impact-melt breccias are also present. One unusual object is a rounded bead, ~200 µm in diameter, and consists of only olivine and plagioclase, partly with a barred texture, similar to a barred-olivine chondrule. One irregular clast consists of plagio-clase, K-feldspar, phosphates, ilmenite, and Si-rich glass, probably representing a mare basalt mesostasis. A fragment composed of ilmenite, baddeleyite, and sulfide was also observed. Most mineral fragments are relatively fine-grained. A few big pyrox-ene grains contain coarse exsolution lamellae (up to 20 µm in width) and the estimated equilibrium temperature interval is 980−700 °C; however, no zoned pyroxene grains were observed. At the same time, a few olivine grains are zoned. Most lithic clasts in Dhofar 1428 are ferroan with Mg# [Mg/(Mg+Fe)] values of mafic minerals varying from 0.51 to 0.78. Only one lithic clast contains Fe-rich olivine (Fo 32) and relatively Fe-enriched pyroxene (Mg# = 0.51–0.61). Most plagio-clase grains in lithic and mineral fragments have An values higher than 94. Olivine grains in the chondrule-like object are Mg-enriched (Fo 80) and have lower Fe/Mn values than other oli-vine grains. In addition, plagioclase grains in the chondrule-like object are relatively Na-enriched (An 87.1–89.5). This unique mineral chemistry supports a possible meteoritic origin. Oxygen isotopic analysis of this object is in process. Glassy fragments have two major compositions. One contains moderate Al 2 O 3 and FeO + MgO contents (15.9–17 wt% and 16.4–18.9 wt%, resp.) and has an Mg# value of 0.5. The other group of glass fragments contains high Al 2 O 3 contents (26.1– 29.7 wt%) and low FeO + MgO contents (8.3–14.4 wt%). The …