The Composition of the Lunar Surface Relative to Lunar Samples

Introduction: The non-mare pristine samples are divided into two major suites, the ferroan anorthosites (FAN) and the Mg-suite [1]. FAN is typically characterized by high values of plagiophile interelement ratios, for example, the calcium content of plagioclase, and very high plagioclase content (though more mafic members exist). FAN is well separated from the Mgsuite on a plot of Mg-number vs. plagiophile element ratios, though there is substantial overlap in both quantities treated in a univariate sense. Presently, plagiophile element ratios are unavailable to remote sensing analysis, so as a proxy, Cahill et al. 2008 (this volume) showed that in lunar samples for which good modes are available Mg-suite and FAN are also well separated on a plot of Mg-number vs absolute plagioclase content. These parameters are available from analysis of spectral reflectance data, including data from Clementine (2), We applied the methods of [2,3] to Clementine data in order to compare the distribution of data moon-wide with the distribution of samples. The remote sensing data is interpolated from immature exposures of lunar material covering about 3% of the lunar surface [3]. Figure 1 shows the distribution of remotely determined plagioclase content and Mg-number, and the distribution of fields for the major lunar rock types on the same diagram. These data are consistent with three units: mare basalt (low plagioclase, low Mg’), FAN (high plagioclase and variable Mg’ with a peak in Mg’ near 75), and Mg-suite norites (low plag and Mg’ near 75).