Abstract:Abstract In this paper, through field investigation, microscopic analyses of samples of the alkaline plutons, 2 samples zircon LA-MC-ICPMS U-Pb dating and 13 samples geochemical researches, alkaline plutons in the eastern of Dong Ujimqi have been studied, for their chronology and tectonic implications. Alkaline granite and quartz-syenite are the rock association of these alkaline plutons and all show the typical mineral of arfvedsonite. The zircon U-Pb dating suggest that these alkaline granites are formed in Early Permian with detail ages of (272.3±0.7) Ma to (271.7±0.7) Ma. Geochemical researches indicate that the alkaline granites are rich in silica (SiO2=72.62%~78.46%), alkali (K2O+Na2O=7.54%~9.80%) and low CaO (0.66%~0.91%), MgO (0.07%~0.31%), with the character of metaluminous-peralkaline (A/CNK=0.87~0.99, NK/A=0.91~1.04). The rocks have moderate REE (146.4×106~389.0×106) , strong Eu depletion (δEu=0.12~0.36) and low grade fractionation of LREE/HREE [(La/Yb)N 3.74~6.83], with enriched in Rb、Th、U、Hf and depleted in Ba、Sr、P、Ti, which indicate the A1-type granites. Compared with alkaline granites (Ba=74×106~207×106), quartz-syenites have high Ba (554×106~1230×106) and slightly Eu anomalies (δEu=0.94~1.24), which maybe induced by the differences of residual minerals as a result of partial melting. Both of them have very low Sr (27.20×106~157.00×106, 2 samples>100×106) and high Yb (2.08×106~7.26×106, except P24-11-1=1.36×106), similar to within-plate granites. Thus, we consider that the alkaline plutons, in the eastern of Dong Ujimqi, had been formed in extensional tectonics, which indicate that ~272Ma maybe the tectonic evolution from Post-Orogenic to Anorogenic in Xing’anling-Mongolia Orogenic Belt.