Beginning and end of lunar mare volcanism

The distribution and characteristics of the early phases of mare vulcanism on the moon are discussed. Breccias have been observed that indicate the presence of magma flows before 3900 Myr BP. A mafic feature has been identified in more than 100 craters at least 1 km across. The absence of buried mare surfaces on the nearside and western hemispheres is attributed to ejecta deposits, and farside basins with no mare fill are suggested to have experienced early mare flooding. Photographs of the bright-rayed Lichtenberg crater have revealed that mare volcanism occurred within the time frame 1700-2000 Myr BP. It is concluded that the moon featured two periods of igneous activity, the last happening at 1000 Myr BP, and beginning 4300 BP.