Lunar Meteorite Dhofar 026: a Shocked Granulitic Breccia, Not an Impact Melt

Introduction: Lunar meteorite Dhofar 026 was previously interpreted as an impact melt [1, 2]. Detailed studies of the rock and comparison to Apollo lunar samples 15418 and 60017 indicate that the rock instead is a shocked, partly melted, granulitic breccia. These studies, presented by [3], are summarized herein. Petrology of Dhofar 026: Most of the rock consists of blocky patches of monomineralic plagioclase, blocky patches of olivine-plagioclase intergrowths, and irregular patches of pyroxene-plagioclase inter-growths (Fig. 1a). Locally the rock contains swirls, streaks, and irregular patches of brownish, plagioclase-rich, devitrified glass and sharply bounded globular bodies that consist of intergrowths of plagioclase and mafic minerals. Vesicles are common throughout the rock. Monomineralic plagioclase. Patches of monomin-eralic plagioclase range from 20 to 300 µm across. The plagioclase is a mat of acicular needles; within many of the larger patches, the needles have similar extinctions. Many patches contain vesicles. Olivine-plagioclase intergrowths. Intergrowths of olivine and plagioclase are as much as 1.5 mm across and consist of small globular olivine grains set in a mat of fine-grained acicular plagioclase. Scattered throughout are sparse 100-µm grains of olivine, which consist of mosaics of small subgrains. Pyroxene-plagioclase intergrowths. Very fine-grained intergrowths of augitic pyroxene, plagioclase, and minor olivine range from small, well-defined patches to irregular anastomosing patches that fill in-terstices between patches of olivine-plagioclase inter-growths and patches of monomineralic plagioclase. Textures and mineralogy of the intergrowths indicate crystallization from melt. The plagioclase, olivine, and some augite grains are subhedral and are enclosed by subophitic-poikilitic pyroxene grains, which are zoned to iron-rich compositions at their edges. Globules. The globules have ovoid to amoeboid to blocky outlines and they average about 100 µm across. Textures and mineralogy indicate crystallization from melt. Olivine forms euhedral or skeletal grains, plagio-clase forms subhedral laths, and augitic, strongly zoned pyroxene and mesostasis fill interstices; the minerals are very fine grained and show no shock effects. The globules commonly contain vesicles. Origin and History of Dhofar 026: The rock is a shocked breccia – a granulitic breccia, or a fragmental breccia consisting almost entirely of clasts of granulitic