Geochemistry and Impact History at the Apollo 16 Landing Site

Lunar impact glasses possess the unmodified refractory element ratios of the original fused target materials at the sites of impacts. These target materials are usually regolith. 866 glasses from the Apollo 16 landing site have been analyzed by electron microprobe in this study. These glasses show significant variation and hint at the existence of highland basalt (HB) regolith compositions atypical of the usual HB compositions historically found at the Apollo 16 site. Additionally, a large number of mare glasses have been identified. Clementine color image data have been used to construct iron, titanium, and aluminum maps for comparison with the sample database. These maps suggest that the Apollo 16 landing site is largely composed of anorthositic material and that mare compositions are not found close by. Nine of these impact glasses have been dated by the Ar-40/Ar-39 technique and may be used to constrain the impact history at the Apollo 16 landing site. These results illustrate how lunar impact glasses together with orbital data can provide geochemical constraints on the local and regional geology of the Moon.