The Batamayineishan Formation from the Kalamaili area of East Junggar is built from a set of basalt- andesite- dacite- rhyolite. The age and tectonic background of its formation have long been disputed. In this paper, based on field investigations and detailed petrological and geochronological research on the Batamayineishan Formation in the Shuangjingzi area, LA- ICP- MS zircon U- Pb dating and petrological geochemical analysis of basalts from the lowermost part this formation were undertaken. The results show that the formation age of the collected basalts is 335. 1± 9. 3 Ma, which belongs to Late Carboniferous epoch. Combined with the previous chronological data and the results of this paper, it is suggests that the Batamayineishan Formation is a diachronic lithostratigraphic unit from Early to Late Carboniferous. Geochemically, basalts samples contains SiO2 of 46. 49%~52. 19%, they have relatively high Na2O+K2O (4. 07%~8. 55%), K2O/Na2O (0. 35~1. 31) and Al2O3 (15. 62%~17. 97%). Their Rittman indices are greater than 3. 3, and alkaline minerals are contained in phenocrysts and matrix, with the typical characteristics of alkaline basalt. The REE patterns of the alkaline basalts are characterized by strongly fractionated REE patterns (La/Yb)N=3. 08~5. 25 and are without Eu anomalies. The concentrations of incompatible trace elements such as Rb, Ba, Sr are enriched, whereas the high field strength element (eg. Nb, Ta and Ti) contents are depleted. Combined with discrimination diagrams, the authors propose that basalts from the Batamayineishan Formation were derived from the partial melting of a depleted mantle that had been metasomatized by subduction- related fluids, possibly with a few additions of continental material. Subsequently, fractional crystallization of mafic- minerals and Fe- Ti oxides occurred during magmatic evolution. Alkaline basalts have the characters of intra- plate basalt, post- collision and arc volcanic rocks. In combination with the regional geological background, alkaline basalts of the Batamayineishan Formation were formed in a post- collision extensional period after the closure of the Karamaili Ocean. It shows that in Late Carboniferous the northeastern Junggar terrane entered a key stage of structural transformation from collisional extrusion to extension.