Absolute time scale of lunar mare formation and filling

Abstract

The high titanium basalts collected in the maria Tranquillitatis and Serenitatis crystallized 3.5-3.9 Ga ago. The ages of the low titanium rocks found in Oceanus Procellarum and on the eastern edge of mare Imbrium are lower, 3.1-3.4 Ga. There is, however, evidence that high-Ti basalts with lower ages and low-Ti basalts with higher ages occur on the Moon. The observed age spread of rocks even in limited areas suggests that lava flow activity in a basin lasted for several 100 Ma. The age variability of Apollo 11 basalts is particularly well documented: there are at least three different times of rock formation, two for the low-K and one for the high-K rocks. The ages of the oldest mare basalts 10003 (high-Ti, low-K rock) and 14053 (an igneous rock with low-Ti, low-K, high-Al mare basalt composition) of 3.91 ± 0.03 Ga and 3.95 ± 0.03 Ga respectively, suggest that mafic basalt flows had already begun to invade the older basins when the last basin-forming impacts occurred.