  We develop a 2-D numerical model of magmatism and mantle convection to
understand the volcanism on the Procellarum KREEP terrane (PKT) of the Moon,
which continued for billions of years with two peaks of activities at 3.5-4 Gyr
ago and around 2 Gyr ago. In our model, the effects of the PKT on lunar
evolution are considered by initially imposing a region of localized
radioactive enrichment. The calculated volcanism has two peaks induced by
different mechanisms. The first peak occurs at 3.5-4 Gyr ago when magma
generated in the deep mantle by internal heating ascends to the surface as
partially molten plumes. The basaltic blocks in the uppermost mantle formed by
this magmatism, then, sink to the deep mantle, triggering further plumes that
cause the resurgence of volcanism at $\sim$2 Gyr ago. Our model shows that
localized radioactive enrichment is important for the long-lasting volcanism
with a couple of peaks.
