A correlation study based on Al/Si x-ray fluorescence data from Southwestern part of mare serenitatis

The Tacquet Formation in southwestern Mare Serenitatis has unusually low visible albedos for the Al/Si intensity ratios measured by the Apollo 15 X-ray fluorescence experiment. This is a contradiction of the demonstrated good correlation between Al/Si and visible albedo data. To understand why this situation exists, a correlation study has been undertaken. This study is based on Al/Si intensity ratios and includes such other remote sensing data as visible and near IR spectral reflectance, color-difference and color-ratio photography, and broad spectrum visible albedo measurements. The Tacquet unit appears to have: (1) an average Al/Si intensity which is intermediate between mare and highland values (=0.21); (2) visible albedos equivalent to the two darkest mare units in the Tranquillitatis-Serenitatis area; (3) a low titanium content; and (4) a relatively high glass-to-crystal ratio. The evidence indicates that the discrepancy between visible albedos and Al/Si intensities in the vicinity of the Tacquet Formation might be due primarily to the addition of highland-type ejecta from the crater, Menelaus, onto a low albedo mare unit. The possibility that the formation consists of dark, high Al material such as spinel, perhaps extruded from the Menelaus Rilles, cannot be excluded, although no such material has been sampled by the lunar missions.