Microcrater and solar-flare track maturation of the lunar regolith

The microcrater, pancake and cosmic ray track record in the 100-200 microns feldspar fraction of a variety of surface soils and Apollo and Luna 16-24 cores have been studied. In Luna 24, a study of the glassy agglutinates plus breccias in 9 levels revealed this core was deposited as discrete layers, most of which are immature. Luna 16 and 20 cores were found respectively mature and immature. Glassy agglutinates and impact microcraters, absent to rare in immature soils such as 12033 and 14141, are present in similar abundances on crystals from submature to mature soils. In submature and mature soils, pancakes are present on 60 to 100 percent of crystals and craters on 50 to 70 percent. Microcrater, track and solar wind gas data suggest feldspar crystals in the size range considered reach an equilibrium maturity grade faster than bulk soils. This is interpreted as due to the limited lifetime of these crystals in the lunar regolith.