Abstract: The Zhajia pluton, emplaced in the Triassic Baryan Har sedimentary basin on the northeastern margin of the Tibet-Qinghai Plateau, consists of high-K calc-alkaline biotite granites. Mafic microgranular enclaves with magmatic textures are also present in the pluton. The granites are characterized by enriched LREE and LILE, and depleted HREE and HFSE. They have moderate negative Eu anomaly （0.5 -0.7）, low end （t）（ -3.5 - -6.2）and moderate initial （87Sr/86Sr） ratios （0.7088 -0. 7090）, and their depleted mantle model ages （tDM） range from 1.1 to 1.3 Ga, while mafic enclaves have lower SiO2 contents, lower end （t） （ - 4. 7 - - 6. 1 ）, higher initial （^87Sr/^86Sr） ratios （0. 7084 -0.7124） and older tDM （1.4 Ga） than the host granites. It is suggested that the early Jurassic Zhajia pluton was formed in post-collisional setting, and granitic magma of the pluton was generated by par- tial melting of the lower crust as a result of the intrusion of mantle-derived magma. The sources of granitic magma might be the mixture of Precambrian Kuhai complex and Wanbaogou group occurring in Kunlun orogenic belt. It seems that there is a Middle Proterozoic basement beneath the Baryan Har sedimentary basin, and the basement is a part of the Western Yangtze platform