They are distinct from the rare peralkaline magmas, which have excess alkali oxides relative to alumina (Na2O + K2O > Al2O3).
[1][2]: Ch6 Alkaline magmas tend to show high titanium oxide (TiO2) content, typically in excess of 3% by weight.
[3] Peralkaline rhyolites (comendite or pantellerite) may be generated by fractionation of alkali basalt magma.
[4] Alkaline magmas are characteristic of continental rifting, areas overlying deeply subducted plates, or at intraplate hotspots.
Alkaline rocks with an age close to 570 million years are common around the perimeters of many continental shields and are evidence of worldwide rifting at that time.