Abstract: Based on the ages determined by K-Ar and Ar-Ar dating methods，the Cenozoic volcanic rocks in the studied region，from early to late，can be subdivided into three series．They are high-K calc-alkaline series (40～30Ma)，leucite basanite-phonolite series (29～ 24Ma) and shoshonite series (1.5Ma)，respectively．The Cenozoic volcanic rocks in northern Tibet，mainly studied by petrochemical and isotope methods，have the characteristics of both WPAB (within plate alkali basalt)and IAB(Inland-arc basalt)．For these three series of rocks，the difference exists not only in their geneses ．but also in their sources ．We interprete that high-K calc-alkaline series was generated by partial melting of crust due to underplating of the basaltic magma from enriched mantle，and underwent the process of crust’s AFC． However， the leucite basanitephonolite series and shoshonite series were evolved from an old enriched mantle related to ancient subduction，and their geneses are attributed to the fractional crystallization in different degrees．From this study，it is clear that the depth of the sources for the Cenozoic volcanic rocks in this area gradually be comes deeper and newer from south to north．