Twenty three samples of alkaline basalts from late Cenozoic volcanic fields of Central Mongolia were dated by potassium–argon method. Analysis of more than 100 K–Ar and Ar–Ar ages showed cyclic temporal variations of potassium in erupted lavas ranged from 0.8 to 4.8 wt %. Alternating high- and moderate-K magmatism took place at 23.4–9.7, 9.6–2.6 Ma, and <1.9 Ma with quasi-periodicity of 6–8, 2.5, and 0.3–0.7 m. y., respectively. It is suggested that high- and moderate-K magmas originated due to processes developed at the lower and upper portions of the Sayan-Mongolian low-velocity
domain (i. e. at depths 120–180 and 80–120 km, respectively).