Tianchi volcano in Changbaishan Mountains is the most famous one in China.The huge volcanic cone of the Tianchi volcano was formed at least by 6 stages of eruptions of basalt and alkali trachyte from the Miocene to the Late Pleistocene.The Miocene basaltic lava conformed the base of the Changbaishan Mountains.The Late Pliocene basalt constructed the shield base for Tianchi volcano.The huge cone was composed of middle to Late Pleistocene alkali trachyte and pantellerite.Activities of the Tianchi volcano during the Holocene have resulted in strong explosion and devastating hazards. The most important activity of the Tianchi volcano in the Holocene is the additional eruption of some basaltic lava and scorias of Laohudong stage(LHD).It is of a central eruption and remained several small cones scattering on the slope of the main volcano,about 3-4 km far away from the crater.In the Laohudong volcano section interbedded basaltic lava and scoria and few trachyte overlie the alkali trachyte base of the Tianchi volcanic cone,indicating that the eruption could be later than the Late Pleistocene and implying that the volcanic activities and the magmatism progress of the Tianchi volcano might be more complex than that suggested before. The discovery of LHD volcanic rocks provides new evidence for the generation and evolution of the Tianchi volcanic rocks.The REE contents of LHD basalt and quartz trachyte are compatible to that of the Miocene to Late Pleistocene basaltic rocks in Changbaishan area and the trachyte of the Tianchi volcano distinctively.From the REE chondrite-normalized patterns,it can be seen that the REE of all samples are gradually enriched with the positive Eu anomaly slightly decreasing in basaltic rocks and the negative Eu sharply depleting from trachyte to pantellerite.Therefore,the LHD rocks should represent and link the basaltic with the evolved magma. The generation process of the rocks in the Tianchi volcano and in Changbaishan area has been discussed by using the Ce/Yb-Ce and La/Sm-La diagrams.On these two correlation diagrams,all basalt plots including LHD are distributed along a partial melting trend,and the plots of trachyte and pantellerite set around a horizontal line,implying that the basaltic rocks from different eruptions were derived from a same magma source by parting melting of mantle material,then transferred to fractional crystallization from basalt through trachyte to pantellerite. Major and trace element discriminations indicate that the basaltic rocks in Changbaishan area have relations to ocean island alkali basalt or ocean flood basalt,instead of an island arc basalt environment,whereas the trachy and pantelleritic rocks were within plate region or anorogenic region.These results are much different from that discussed with the subduction of West Pacific Plate before.Therefore,the tectonic genetic process involved in the formation of the Cenozoic volcanic rocks and the activity of the Tianchi volcano was not related directly to the subduction and a comparative research with the volcanic rocks in the Cheju Island of Korea might be necessary.