稀土和大离子亲石元素( Ｒb、K) 和高场强元素( Th、U) ，显著亏损重稀土及高场强元素( Ta、

Nb、Ti) 和P 元素，显示了俯冲带岩浆岩的地球化学特征。锆石的εHf ( t) 值在+ 5. 82 ～ + 10. 15 之

间，二阶段模式年龄在826 ～ 581 Ma 之间，揭示其岩石源区可能来自新元古代—显生宙期间亏损地幔或亏损地幔形成的基性下地壳物质的再熔融，具有幔源和壳源岩浆混合的特点。结合区域地质资料，认为科右中旗地区闪长玢岩应形成于早白垩世区域伸展环境，是蒙古—鄂霍茨克洋闭合碰撞之后加厚陆壳的拆沉、幔源岩浆底侵的结果。

Keyouzhongqi area of Great Xing'an Ｒange，the formation age，petrogenesis and tectonic setting of diorite porphyrite were analyzed． LA--ICP--MS zircon U--Pb dating results show that diorite porphyrite formed in the Early Cretaceous

with ages of ( 132. 4 ± 1. 2) Ma to ( 130. 8 ± 2. 7) Ma． The ( Na2O + K2O) content of diorite porphyrite is 6. 20% ～ 7. 92%，and the aluminum saturation index A/CNK is 0. 83 ～ 0. 95． It belongs to the series of quasialuminum high potassium calcium alkali rocks． The diorite porphyrite is enriched in large ion lithophile elements ( Ｒb，K) and high field strength elements ( Th，U) ，but depleted in heavy rare earth and high field strength elements ( Ta，Nb，Ti) and P element． It shows the geochemical characteristics of magma rock in subduction zone． The εHf ( t) values of the zircons range from + 5. 82 to + 10. 15，and the two-stage model age ranges from 826 to 581 Ma． This indicates that the source of the rocks may be from the remelting of the basic lower crust material formed by the depleted mantle or the depleted mantle during the Neoproterozoic to Phanerozoic，and is characterized by the mixing of mantle derived and crust derived magma． Combined with the regional geological data，it is concluded that diorite porphyrite in the Keyouzhongqi area should have been formed in the regional extensional environment of Early Cretaceous，resulted from the underplating of mantle-sourced magma and the delamination of thickened continental crust after the closing collision between Mongolia and Okhotsk Ocean．