1. College of Earth Sciences, Jilin University, Changchun 130061, China;
2. International Centre for Geoscience Research and Education in Northeast Asia, Jilin University, Changchun 130026, China

LA-ICP-MS zircon U-Pb dating and geochemical data of Simuke porphyritic syenogranite have been studied.The results indicate that the diagenetic age of porphyritic syenogranite is (144±0.85)Ma,belonging to Late Jurassic.The geochemical study shows that the porphyritic syenogranite belongs to high-K calc-alkaline series and high aluminum rocks. The rare earth elements are characterized by rich light rare earth elements and significant fractionation of LREE and HREE[(La/Yb)_N=3.15��6.63].The REE distribution patterns are right deviated, with weak negative europium anomalies(δEu=0.54��0.66). For trace elements, the porphyritic syenogranites are enriched in Rb and K,but depleted in Nb,Ta,P and Ti.The porphyritic granite in Simuke area is high differentiation I type granite,derived from partial melting of basic volcanic rocks in the crust.Based on Nb-Y tectonic environment discrimination diagram and tectonic environment,combined with the characteristic of I type granite,the porphyritic granite in Simuke area should be the product of extensional tectonic system and it is formed in post-orogenic extensional tectonic environment.