The syenogranite in Qinghai Province is located on the east periphery of the Kendekeke deposit in the Qimantag area, East Kunlun Mountains. It consists of alkali feldspar (50%~60%), quartz (20%~30%), plagioclase (10%~20%), and biotite and hornblende (1%~5%). The results of LA-ICP-MS zircon U-Pb isotope dating reveal that the syenogranite was formed at 217.9±1.7 Ma (MSWD=0.74, n=20), suggesting the Late Triassic and the same time as the metallogenic age of the iron-polymetallic deposit in Qimantag area. The syenogranite is characterized by high silicon (SiO₂=74.62%~75.28%), high alkali (K₂O + Na₂O=8.81%~8.95%), and fairly high ratio of FeO^T/MgO (18.02~31.48). The trace element and REE compositions show the features of significant negative Eu anomalies (δEu=0.04~0.05), enrichment of Rb, Th, U, K, Ga, and depletion of Sr, Ba, Ta, P, Ti. The geochemical characteristics indicate that the syenogranite belongs to metaluminous-weakly peraluminous A-type granite. The εHf(t) values of syenogranite vary from 2.0 to 12.4 with the two-stage model ages being t_DM2 of 1 126~458 Ma. It is held that the source region of syenogranite probably had a mixture with the mantle and ancient crust, which provided abundant materials for the iron-polymetallic mineralization in this area. In the discrimination diagrams of A-type granite, the syenogranite falls into A2-type granites, which suggests that it was formed in an extensional tectonic regime after the orogenic process. All these characteristics display a transition of the Late Variscan-Indosinian orogenic cycle from the epi-orogenic stage to the extensional tectonic regime in Qimantag area in the late Triassic.