Glasses of impact origin from Apollo 11, 12, 15, and 16 - Evidence for fractional vaporization and mare/highland mixing
Electron microprobe analyses have been performed on glasses of impact origin in Apollo 11 breccias (10059, 10060, 10061), Apollo 12 soil (12070), and Apollo 15 breccias (15318, 15425, 15426, 15427). These glasses were produced by shock melting of regolith, rather than of rock. Simple concepts for better understanding and interpreting the chemical data from impact glasses have been developed. These concepts are a significant improvement on earlier strategies, which centered principally on cluster analysis. Using ratios of refractory lithophile elements, the compositional effects of fractional vaporization often associated with impact melting to obtain chemical information about the mare and highland components in the regoliths parental to the glasses have been 'seen through'. This method is also applied to the mare-derived impact glasses from Apollo 16 in order to place constraints on the types of volcanic components occurring in Mare Nectaris. Since impact glasses can be used to derive chemical constraints on the indigenous lithologies comprising multi-component regoliths; the frequent occurrence of these glasses, as well as their low masses, should make them critically important for study when small quantities of grab-samples are returned by future unmanned spacecraft from planets, satellites, and asteroids where regoliths are present.