Lunar volcanism in space and time

The role of lunar volcanism in the history of the moon is documented using lunar-orbit and earth-based data along with characterizations derived from Apollo and Luna sample-return missions. Characteristics of mare and highland volcanic features are described, Apollo and Luna results are discussed, and the characteristics of other mare deposits and of other highland features of possible volcanic origin are summarized. Major conclusions are that: (1) there is little unequivocal morphologic evidence for highland volcanism, (2) lunar mare lavas appear to have originated from depths of 100 to 500 km, (3) impact melting does not appear to have been a factor in the generation of mare lavas, (4) mare volcanism was characterized by massive outpourings of very fluid volatile-poor lava analogous to terrestrial flood basalts, (5) mare volcanism took place from 3.83 to about 2.5 billion years ago, (6) the preferential occurrence of mare deposits in large impact basins appears to be generically unrelated to basin formation, and (7) a thicker farside crust may be responsible for the distinctive nearside-farside asymmetry of mare deposits.