The Sailipu potassic-ultrapotassic volcanic rocks in western Lhasa block,Tibetan plateau,are trachyandesite with mantle- derived xenoliths.The high contents of K_2O,MgO,Cr,Ni,high K_2O/Na_2O ratio and Mg~# of the rocks suggest a primitive magma of mantle low-degree partial melting,or some fractionation of olivines,clinopyroxenes and Fe-Ti oxides.The rocks also show extremely enrichment of LILE,LREE,significant negative Nb,Ta and Ti anomalies,enrichment in radiogenic Sr,Pb and Nd,those of which suggest that an enriched mantle source region should have been responsible for the Sailipu magmatism.LA-ICP-MS has been carried out on dating 18 new zircons from Sailipu potassic-uhrapotassic rocks,and gives U-Pb ages between 15.8Ma and 19.2Ma.The weighted mean of 11 U-Pb analyses for potassic sample SL0628 is 17.7±0.3Ma,in agreement with previous ~(40)Ar/~(39)Ar data.These zircons havee_(Hf)(t) values from-7.6 to 3.9,yielding a wide range of crustal Hf model ages (t_(DMC)=0.86～1.59Ga),generally showing enriched characteristics except two analyses.This indicates that they were derived from an enriched source with a little depleted mantle materials involved.49 inherited zircons,obtained from three samples,have U-Pb ages from 20Ma to 1907Ma,wide ranges of Hf isotope (e_(Hf)(t)=-25.9～5.3) and crustal Hf model ages (t_(DMC)=0.79～4.08Ga).Among the above 49 zircons,37 inherited ones,with younger U-Pb ages between 20 to 110Ma,suggest the mantle source may have experienced four stages of magmatism (62.2～64.0Ma,43.3～55.1Ma,29.5～37.7Ma and 20.1～27.4Ma) and two magmatic gaps (70～90Ma and 37.7～43.3Ma).We also identify a significant,previously unknown stage of magmatism between 29.5Ma and 37.7Ma in Lhasa block,and find a magmatism stage with ages at the end of Linzizong volcanic rocks but enriched Hf isotope (62.2～64.0Ma,e_(Hf)(t)=-21.2～3.0).The above Hf analyses of 49 inherited zircons suggest enriched compositions in mantle source were derived from Lhasa block and Indian continental crust.The potassic-ultrapotassic magma in Sailipu was possibly resulted from the tearing of the Indian continental slab and diachronous subduction along the Indo-Asian collision zone.