Integrated Spectral Analysis of Mare Soils and Craters:Applications to Eastern Nearside Basalts

High spatial resolution Clementine images are examined to measure the reflectance properties of small and optically immature mare craters that have sampled discrete compositional units. The spectral properties of these relatively crystalline mare materials are compared to associated mature soils to determine the effects of space weathering on specific basalt types. Space weathering is observed to alter the optical properties of distinct lunar basalt units in a systematic manner allowing compositional distinctions to be recognized across maturity states. Ultraviolet/visible reflectance properties of mare basalts are sensitive to titanium content but are relatively independent of maturity state and demonstrate only a slight reddening as regoliths mature to soils. Other compositional distinctions between basalt types are identified by differences in albedo and band strength of ferrous minerals that are maintained over a full range of maturity states. Immature deposits within large craters are compared to the spectral properties of well-defined mare units to examine the composition of buried materials. When craters excavate through the mare, highland contamination is readily identified as a mixing relation between mafic and feldspathic lithologies. The approach presented here provides new information on the composition and stratigraphy of several nearside mare deposits, including the identification of thin low-iron and very low titanium basalts in Lacus Somniorum and more iron-rich low-titanium basalts in eastern Mare Frigoris. c © 2000 Academic Press