【摘要】 高精度同位素年代学和岩石学、元素地球化学研究结果表明,吉林省中部地区存在晚三叠世和早侏罗世两期铝质A型花岗岩。其中三道河正长花岗岩的锆石LA ICPMS年龄为(216±3) Ma,形成于晚三叠世,受控于华北板块和其北侧板块在晚二叠世—早三叠世沿西拉木伦河—长春—延吉缝合带碰撞拼合后的岩石圈伸展作用,标志古亚洲洋构造域的演化结束。天桥岗碱长花岗岩的锆石SHRIMP和TIMS年龄分别为(182±3) Ma和(188±4) Ma,全岩Rb Sr等时线年龄为(185±4) Ma,形成于早侏罗世,可能是与佳木斯板块和松嫩—张广才岭板块在早侏罗世早期沿嘉荫—牡丹江缝合带碰撞拼合有关的伸展作用的产物。这次板块碰撞作用很有可能标志着东北地区东部此时已经开始进入滨太平洋构造域的演化阶段。更详细的研究显示,两期A型花岗岩岩浆都来源于年轻的基性玄武质下地壳的部分熔融,岩浆经历了分离结晶作用。更多还原

【Abstract】 Geochronological, petrological and geochemical research shows that there are two episodes of A-type granite intrusions during the Late Triassic and the Early Jurassic in central Jilin Province.Zircons from Sandaohe syenogranite yield an age of 216±3 Ma. The intrusion of this syenogranite was controlled by post-orogenic extension of the Xilamulun River-Changchun-Yanji suture belt, between the North China Craton and the plates to the north. The emplacement of this syenogranite marks the closure of the Paleo-Asia Ocean. The Tianqiaogang alkali-feldspathic granite was intruded in the Early Jurassic, based on SHRIMP and TIMS zircon U-Pb ages of 182±3 Ma and 188±4 Ma respectively, and whole rock Rb-Sr isochron age of 185±4 Ma. The emplacement of this granite marks the orogenic-associated extension of Jiayin-Mudanjiang suture zone, between the Jiamusi Plate and the Songnen-Zhangguangcai Plate, which amalgamated during the late Triassic to the early Jurassic. More detailed research suggests that these two episodes of A-type granite intrusions originated from the partial melting of young mafic lower crust,and that the melts experienced fractional crystallization.更多还原