In the Mesozoic, during the Jurassic, ring complexes known as the Younger Granites intruded Neoproterozoic and Paleozoic basement rocks in the Jos Plateau, as well as in the Air region in Niger. The Younger Granites are primarily alkali-feldpsar granites, although the ring complexes also include rhyolite, gabbro and syenite. The ring dikes tend to be highly mineralized and enriched in niobium and tin.