The relative and absolute age determination of rilles in southwest Aristarchus region

In this paper, we estimated the relative and absolute ages of the seven rilles (1-7) in southwest Aristarchus region in order to know when these lunar rilles formed and how they fit into lunar volcanic history. According to their superposition relationships and colors in the color-ratio composite, the geological units and features in the study area were sorted in an order from old to young: the highland materials, the glassy Fe2+ rich pyroclastics (DMD), the rille 1, 2, 3, 5, and 7, the mature and fresh basaltic units in the east and south of the Aristarchus plateau, the rille 4 and 6, the youngest Aristarchus Craters and its ejecta deposits. Buffered Crater Counting (BCC) method provides a chance to determine ages of linear features that do not have enough surface areas for the traditional crater counting method. The BCC analysis of seven rilles had shown that five of them probably formed in the Imbrium Period and the other two formed in Eratosthenian Period. The absolute age of oldest rille is 3.77−0.04+0.03Ga and the youngest rille׳s age is 1.49−0.26+0.26Ga. Because their formation is interpreted to lava flowing and eroding of magma eruptions, we can see that the volcanic activities in Aristarchus region lasted for a long time from Pre-Nectarian Period (DMD materials) to Eratosthenian Period (rille 6) and weakened gradually to form small scale rilles as times went on. This may be because of the basaltic volcanic eruptions produced by heating elements in Aristarchus region to partially melt the underlying lunar mantle, which become the materials and source of these rilles.