Objectives: This paper presents zircon UPb ages dating results and geochemical data of the basalts of the Tamulangou Formation in the Xinlin area, north Da Hinggan Mountain, with the aim of constraining the origin of the basalts and the nature of the Mesozoic lithosphere mantle. Methods:Pulverization of the volcanic rock samples and the selection of zircons for analysis were undertaken at the Regional Geological Survey Research Institute based in Langfang City, Hebei Province,China. The samples were pulverized to 80~100 mesh, elutriated, and separated using the electromagnetic method. Zircons with good crystal shape, and lacking any significant inclusions or cracks, were selected using a binocular microscope. The preparation of the zircons for observation under transmitted and reflected light, cathode luminescence imaging, and UPb isotopic analysis, was completed in the Tianjin Institute of Geology and Mineral Resources, Tianjin, China. Results:The zircon UPb ages dating results indicate that basalts of the Tamulangou formed in the Late Jurassic (~153Ma). They have SiO2=49.96%~59.06%, Na2O+K2O=5.21%~7.44%, and Mg# ={100×n(Mg2+)/［(n(Mg2+)+n(Fe2+)］}=50~94。These basalts are enriched in light rare earth elements (LREEs), and depleted in heavy rare earth elements (HREEs), LaN/YbN=10.7~20.0, and have weak Eu anomalies (δEu=0.80~1.09). Conclusions:Combined with the studies on the regional geology, suggesting that the basalts of the Tamulangou Formation formed under the a lithospheric extension setting related to the closure of Mongol—Okhotsk Ocean, and were derived from partial melting of spinel lherzolite and garnet lherzolite. the source of this magma contain amphibole, phlogopite that rich in volatile, indicating that they had experienced mantle metasomatism. and that the metasomatizing agents are mainly subduction fluid/melt. Combined with the regional research results, we suggest that the mantle metasomatic fluid/melt could be originated from southern subduction of Mongol—Okhotsk Ocean crust, and these volcanic rocks formed under a lithospheric extension after the closure of Mongol—Okhotsk Ocean.