Fig. 4

The ages of the mare units in the study area. Solid circles with error bars indicate the ages determined in this study. The bars depict the plus–minus standard deviations. Open circles indicate the ages determined in previous studies; H, Hiesinger et al. (2000); B (Bugiolacchi and Guest 2008); M (Morota et al. 2011); Q (Qiao et al. 2014). In cases where their divisions of the mare units are significantly different from ours, their ages are not shown in this diagram