The Paleozoic era experienced the evolution of Paleo- Asian tectonic regime in the Northeast China, the Mesozoic experienced the transition from Mongol- Okhotsk to Western Pacific tectonic regime, in this period forming different temporal magmatic activities. Zircon U- Pb dating and whole- rock geochemical analyses are undertaken for the granitic mylonites in Lingxia area, Baicheng city of Jilin province， the western of the Songliao Basin, with the aim of constraining its emplacement time, petrogenesis and the regional tectonic setting. Zircons from the granitic mylonites in Lingxia area are euhedral- subhedral in shape, and display fine- scale oscillatory growth zoning, indicating a magmatic origin. LA- ICP- MS zircon U- Pb dating indicates that the country rock of granitic mylonites formed in the Early Permain (281.9±7.4Ma and 296.2±2.7Ma). The granitic mylonites have SiO2=64.10%～75.98%, Al2O3=11.22%～16.00%, Fe2O3=0.23%～0.85%, and belong chemically to metaluminous- peraluminous series (A/CNK=0.97～1.19). In addition, these granitic mylonites are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE), and depleted in heavy rare earth elements (HREE) and high field strength elements (HFSE). The above features indicate that the primary magma was derived from partial melting of dehydrated thickened crust under high temperature and high pressure. Combined with the regional geological features, we conclude that the granitic mylonites in the Lingxia area emplaced in a extensionism setting of back- arc, which is related to the closure of the Paleo- Asia ocean; the age (157～153Ma)of metamorphic magma thermal events in the granitic mylonites is related to the closure of the Mongol- Okhotsk ocean; the main deformation time (137～117Ma) of the granitic mylonites is the Mid- stage of early Cretaceous, its limits on the starting time of the Western Pacific Izanagi plate obliquely subducting under the Eurasia plate.