Strongly alkaline volcanism includes Na-rich series (e.g., basanite, nephelinite) and K-rich series (e.g., lamproite, leucitite), predominantly occurring in intraplate settings. Na-rich volcanism is associated with thin lithosphere (100 km).

Partial melting of volatile-free four-phase peridotite (olivine, clinopyroxene, orthopyroxene, garnet/spinel) can generate tholeiitic basalt and mildly alkaline volcanism (e.g., alkali basalt), but does not readily produce strongly alkaline volcanism. The similar partitioning behaviour of K, Nb, and La during peridotite melting prevents a pronounced K-trough in primitive mantle-normalised trace element patterns of tholeiitic and alkali basalts. In contrast, such a feature is present in Na-rich and most K-rich strongly alkaline volcanism. This suggests the involvement of an additional K-rich phase that remains partially unmelted.

Experimental studies show that amphibole- and phlogopite-bearing peridotite sources yield melts resembling Na-rich strongly alkaline volcanism, while phlogopite-bearing sources match K-rich volcanism. This implies that phlogopite is the key K-rich phase required for strongly alkaline volcanism generation. The stability fields of amphibole (3 GPa and amphibole ± phlogopite at pressures

These findings suggest that the ultimate precursors of strongly alkaline volcanism, originating from the sublithospheric mantle (as their isotopic compositions broadly resemble OIBs), temporarily reside within the lithosphere. There, amphibole ± phlogopite stabilise at depths 100 km. Subsequent remelting of this modified mantle produces Na-rich strongly alkaline volcanism in regions with thin lithosphere (100 km). Thus, the global distribution of intraplate strongly alkaline volcanism is controlled by the stability of hydrous minerals.