吉林桦甸地区东南岔组下段变质砂岩碎屑锆石U-Pb年代学研究

U-Pb dating of detrital zircons of metamorphic sandstone from Dongnancha formation in the Huadian area of Jilin Province

为了讨论吉中桦甸地区东南岔组下段所属时代和物源,采用碎屑锆石U-Pb年代学和全岩地球化学分析方法对东南岔组下段变质砂岩进行研究,其所属时代和物源对了解东北地区晚古生代的构造演化具有重要意义。U-Pb定年分析结果显示,东南岔组下段形成时代介于250~222Ma,为三叠纪,并不是前人所认为的古生代。全岩地球化学分析结果显示,东南岔组下段变质砂岩原岩物源形成于大陆岛弧或活动大陆边缘。物源来自吉中古生代岩浆岩、松嫩地块早古生代变质基底、华北板块和少量松嫩—张广才岭地块新元古代地质体,具有造山带和大陆双向来源的二元物源供给特点。东南岔组下段变质砂岩可能形成于陆-陆碰撞后的前陆盆地构造背景下,表明吉林桦甸地区古亚洲洋可能于222~250 Ma闭合。

To constrain the age and provenance of the lower member of the Dongnancha formation in the Huadian area of central Jilin Province,detrital zircon U-Pb chronology and whole rock geochemistry were investigated,which is very important for understanding late Paleozoic tectonic evolution of the Northeast China.The result of U-Pb chronology indicate that the lower part of Dongnancha formation formed between 250 and 222Ma,Triassic,not Paleozoic as previously thought.The whole rock geochemistry indicate that the original provenances of metamorphic sandstone formed under the continental island arc or active continental margin.The provenances mainly came form Paleozoic magmatic rocks around the studied area,early Paleozoic metamorphic basement of the Songnen Block,North China Plate and some Neoproterozoic igneous rocks of the Songnen-Zhangguangcailing Massif.Geochemical characteristics show that the tectonic setting of the metamorphic sandstone should be foreland basin,and the PaleoAsian Ocean probably was closed between 222 and 250 Ma in region of Huadian,Jinlin Province.