The University of Arizona

Comment on: "New" lunar meteorites: Impact melt and regolith breccias and large-scale heterogeneities of the upper lunar crust, by P. H. Warren, F. Ulff-Mller, and G. W. Kallemeyn

O. B. JAMES, B. A. COHEN, L. A. TAYLOR, M. A. NAZAROV

Abstract


We described lunar meteorite Dhofar 026 (Cohen et al. 2004) and interpreted this rock as a strongly shocked granulitic breccia (or fragmental breccia consisting almost entirely of granuliticbreccia clasts) that was partially melted by post-shock heating. Warren et al. (2005) objected to many aspects of our interpretation: they were uncertain whether or not the bulk rock had been shocked; they disputed our identification of the precursor as granulitic breccia; and they suggested that mafic, igneous-textured globules within the breccia, which we proposed were melted by post-shock heating, are clasts with relict textures. The major evidence for shock of the bulk rock is the fact that the plagioclase in the lithologic domains that make up 80-90% of the rock is devitrified maskelynite. The major evidence for a granulitic-breccia precursor is the texture of the olivine-plagioclase domain that constitutes 40-45% of the rock; Warren et al. apparently overlooked or ignored this lithology. Textures of the mafic, igneous-textured globules, and especially of the vesicles they contain, demonstrate that these bodies were melted and crystallized in situ. Warren et al. suggested that the rock might have originally been a regolith breccia, but the textural homogeneity of the rock and the absence of solar windderived noble gases preclude a regolith-breccia precursor. Warren et al. classified the rock as an impact-melt breccia, but they did not identify any fraction that was impact melt.

Keywords


melting;Impact breccia;Impact;lunar Meteorites

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