The duration of volcanism in Mare Serenitatis

The crystallization ages of a suite of Apollo 17 basalts from four different stations have been measured using the Ar-39 to Ar-40 stepwise heating technique. The rocks analyzed include all principal petrographic types found at Apollo 17 landing site. A correlation between the ages and the petrographic type exists; plagioclase-poikilitic ilmenite basalts are youngest and olivine porphyritic ilmenite basalts are the oldest. The duration of volcanism in Mare Serenitatis is about 200 million years, the same as observed for Mare Imbrium, and less than observed for Mare Tranquillitatis, 400 million years. A relationship between duration of volcanism and gravity anomalies is noted. The cosmic ray exposure ages (in millions of years) for various locations range as: station 4, 58-315; station 5, 85-440; station 6, 110; station 8, 90-160.