Geology of mare deposits in South Pole‐Aitken basin as seen by Clementine UV/VIS data

Abstract

A multispectral analysis of 21 discrete lunar mare deposits within the South Pole‐Aitken basin was undertaken in order to model the general mineralogical composition of farside mare deposits so that the near‐ and farside may be compared in terms of magma generation and emplacement. Determination of each deposit's mineralogy was based upon albedo, the 0.75/0.95 μm ratio indicating the presence of a 1.0 μm absorption band, and the strength and shape of that band. A combination of improved spatial resolution and the availability of the general multispectral signature for each pond allowed deposits to be examined for homogeneity in order to assess the nature and number of flows represented. FeO and TiO2 abundances were also estimated. Based upon the resultant data, 19 out of 21 ponds were determined to be mare deposits. Of these 19, 15 had spectra well‐defined enough to classify general mineralogy, nine having high‐Ca pyroxene signatures indicative of basalt and six showing low‐Ca signatures suggesting a substantial noritic component. We believe these noritic signatures can plausibly be attributed to vertical/lateral soil mixing processes for the smallest ponds, although a unique lithology cannot be ruled out for the largest pond. A majority of ponds in this study region have homogeneous spectral signatures, interpreted to represent individual eruptive phases. This indicates that very large volumes for these regions may be typical. Also, because such volumes are comparable to the largest terrestrial eruptions, they may have formed by a similar mechanism of emplacement. The vast majority of mature soils are spectrally redder (and thus have a lower estimated FeO abundance) than the Mare Serenitatis soil standard (MS‐2) in particular, and nearside basalts in general. These soils also average low to medium estimated TiO2 abundance, similar to Apollo 12 and 15, and Luna 24. The observations made here are consistent with a scenario in which basalts with low FeO and low to medium TiO2 contents were deposited during the lunar peak volcanic period that occurred in the Late Imbrian (3.80–3.20 Ga) and because of their small areal extent were more susceptible to mixing processes than nearside basalts.