Lunar mare basalts in the Aristarchus region: Implications for the stratigraphic sequence from Clementine UVVIS data

Abstract

The Aristarchus region of Oceanus Procellarum is an area concentrated with lunar basalts, which were mainly produced by the last major phase of lunar volcanism on the western nearside. A group of lunar sample and remote sensing scientists have carried out the extensive task of characterization of lunar mare soils with regard to their mineralogical and chemical makeup and regional geologic mapping. Spectral parameters of the high spatial resolution Clementine images are used to identify and define these basalts as different compositional and spectral units. This endeavor is aimed at deciphering the subtle spectral characteristics of mare soils and validating the mapping technique used in this study, together with making statistical analysis of the links between the basalt types with ages in order to provide a further understanding of material types and geologic evolution in the Aristarchus region of the Moon. From the new perspective of mining geologic information in multivariable image-spaces, spectrally distinct 9 high-Ti and 11 low-Ti basalt reference spectra have been distinguished and as a result, more than 70 spectrally and compositionally basaltic units, which range in age from 1.20b.y. to 3.74b.y., have been identified. To some extent, a potential relationship between composition and relative age exists in the statistical analysis of the links between spectral types (related with the Clementine ratio colors) of various basalts and ages in this study, which suggests that composition with different states of maturity correlate with age to some extent. The mineralogical characteristics and spectra-age relationship in the Marius Hills region indicate that the early basalts may still be exposed at the surface deposit after prolonged volcanic activity in this region. This may be a result of not being blanketed by later lava flows, or lava extrusions of underlying low-Ti basalts. In addition, stratigraphic analysis also reveals and confirms that TiO2 concentrations appear to vary independently with time, and generally eruptions of TiO2-rich and TiO2-poor basalts have occurred contemporaneously.