LUNAR-SURFACE ALUMINUM AND IRON CONCENTRATION FROM GALILEO SOLID-STATE IMAGING DATA, AND THE MIXING OF MARE AND HIGHLAND MATERIALS

Apollo X ray spectrometer data provide chemical information for 9% of the lunar surface. Galileo solid state imaging system (SSI) multispect ral data for the Moon are employed to reexamine the long-accepted posi tive correlation between lunar surface reflectance (or albedo) and alu minum concentration, derived from Apollo X ray spectrometer data. The overall goal of the analysis is to quantify the relationship between r eflectance and aluminum, and to take advantage of the extensive spatia l coverage of the SSI data (similar to 75% of the lunar surface) to ca lculate aluminum concentration from SSI reflectance for the majority o f the lunar surface. After removing nonmature highlands from the analy sis, it is found that the relationship between lunar surface reflectan ce and X ray spectrometer-derived aluminum concentration is described by two diffuse endmembers, representing highland and mare materials, a nd an apparent mixing line suggestive of mixtures of mare and highland materials. Regression analysis is utilized to show that whereas the c orrelation between reflectance and aluminum for the entire lunar soil system is fairly good, the correlations for mare soils alone and for h ighland soils alone are extremely low. The low precision of the X-ray data may at least in part be responsible for the observed poor correla tions. Although the low correlation for the individual soil types prec ludes the precise calculation of aluminum concentration from reflectan ce, approximate aluminum contents can be determined. The excellent inv erse correlation between aluminum and iron concentration for returned lunar soils allows an estimation of iron content to be made as well. A n extensive zone of mixtures of mare and highland soils exists in the vicinity of mare-filled impact basins, and around smaller craters. Thi s zone occurs in morphologically defined mare and highland units. Phys ical mixing of more mafic and less mafic material due to vertical and lateral transport by impact and downslope movement can account for the widespread mixing zones.