Integrated spectral analysis of mare soils and craters: Applications to eastern nearside basalts

High spatial resolution Clementine images are examined to measure the refle ctance properties of small and optically immature mare craters that have sa mpled discrete compositional units. The spectral properties of these relati vely crystalline mare materials are compared to associated mature soils to determine the effects of space weathering on specific basalt types. Space w eathering is observed to alter the optical properties of distinct lunar bas alt units in a systematic manner allowing compositional distinctions to be recognized across maturity states. Ultraviolet/visible reflectance properti es of mare basalts are sensitive to titanium content but are relatively ind ependent of maturity state and demonstrate only a slight reddening as regol iths mature to soils. Other compositional distinctions between basalt types are identified by differences in albedo and band strength of ferrous miner als that are maintained over a full range of maturity states. Immature depo sits within large craters are compared to the spectral properties of well-d efined mare units to examine the composition of buried materials. When crat ers excavate through the mare, highland contamination is readily identified as a mixing relation between mafic and feldspathic lithologies. The approa ch presented here provides new information on the composition and stratigra phy of several nearside mare deposits, including the identification of thin low-iron and very low titanium basalts in Lacus Somniorum and more iron-ri ch low-titanium basalts in eastern Mare Frigoris. (C) 2000 Academic Press.