2. International Centre for Geoscience Ｒesearch and Education in Northeast Asia，Jilin University，Changchun 130026，China;

3. Institute of Petroleum Geology and Exploitation，No. 1 Oil Producing Plant of Qinghai Oil Field，PetroChina，

Dunhuang 736202，Gansu，China

during the Early Cretaceous with the age of ( 132 ± 2) Ma． The geochemical data shows that the granodiorite samples in the study area are characterized by high silicon ( SiO2 = 66. 68% ～ 68. 09%) and low aluminum ( Al2O3 =

14. 94% ～ 15. 35%) ，and enriched in light rare earth elements ( LＲEEs) and large-ion lithophile elements( LILEs; e. g.，Ｒb and K) ，and depleted in heavy rare earth elements ( HＲEEs) and high field strength elements( HFESs; e. g.，Nb，Ta and Ti) ，suggesting that they are high-K calc-alkaline I-type granites． Based on the petrological and geochemical characteristics of the Mesozoic granites in the region，it is suggested that the Early Cretaceous I-type granites represented by the Wulanmaodu granodiorite may have formed in the active continental margin

environment，and that the tectono-magmatism of this period is closely related to the subduction of the Paleo --Pacific plate．