1. College of Earth Sciences, Jilin University, Changchun 130061, China;
2. College of Resources and Environment Science, Jilin Agricultural University, Changchun 130118, China

Through the study of field geology, Zircon U-Pb dating results, and characteristics of relevant geochemical elements of granite porphyry in Suolun area in Inner Mongolia, the formation age of granite porphyry was determined, petrogenesis and tectonic background of granite porphyry are discussed. Granite porphyry in Suolun area usually occurs as beads or dikes. The LA-ICP-MS Zircon U-Pb isotope dating results show the granite porphyry formed in late Early Cretaceous (119.9 ±1.6 Ma). The rocks are rich in silicon, alkali and aluminum, and belong to the series of aluminum-peraluminous high-potassium calc-alkaline. Mineral assemblages and geochemical element analysis exhibit that the granite porphyry is highly fractionated I type granite, and is characterized by the enrichment of large ion lithophilic elements(Rb,Th,U)and light rare earth elements(La,Ce,Pr)with obvious negative anomalies of Eu, indicating geochemical characteristics of crust-sourced magma or magma mixed with crustal materials. Granite porphyry in Suolun area has positive ��_Hf(t) values of +7.5~+10.8, and two-stage model ages of 489 Ma to 695 Ma, which indicated that the source materials may have formed from the melting of the basic lower crust material in the Early Paleozoic and Neoproterozoic. The granite porphyry was formed in the post-orogenic extensional environment in Suolun area, which may be related to the delamination of the thickened continental crust after the closure of the Mongol-Okholsk suture zone.