Abstract: Cenozoic volcanic rocks are discovered in northern Gemucuo area during 1∶250000 Mayigangri regional geological investigation. 40Ar/39Ar dating are carried on three samples from this volcanic rocks amd yield the plateau ages of 30.6±0.4 Ma, 30.0±0.2 Ma and 29.8±0.3 Ma, which represent the volcanic eruption age. The geochemical characters of the volcanic rocks in the northern Gemucuo are similar with potassic volcanic rocks, together with the Cenozoic volcanic rocks distributing at Yulinshan, Zougouyouchacuo, duogecuoren etc. constitute, the Cenozoic potassic -ultrapotassic volcanic belt in Qiangtang area. The formation of these volcanic rocks has relations with the collision between India and Asia and uplift of Qinghai-Tibet plateau.