On the boundary of the mountainous highlands and the solidified lava plains of Oceanus Procellarum lies the lava-flooded Letronne crater.
The lava-flooded crater of Letronne, stretching 120 km in diameter, captured by Apollo 16. Source: Apollo Image Archive
The northern part of the crater rim is completely absent. Only the southern rim and a part of the central peak are visible. The region of Letronne crater was filled with lava during the time of active volcanism on the Moon. But here's the thing, the crater formed later, not before the lava flood!
When scientists studied ejected material from the crater, they found that it consists of a mix of highlands and mare materials. It implies that both highlands and mare materials were present in the impact area before the crater was formed.
Further analysis of this and other regions will lead to a greater understanding of lunar tectonism as well as lunar volcanic processes.