内蒙古东部索伦二叠纪哲斯组碎屑锆石U-Pb年龄及其大地构造意义

内蒙古索伦地区位于贺根山-黑河断裂和西拉木伦河-长春-延吉断裂之间,该区发育巨厚的二叠系哲斯组地层。研究其年代学特征对确定该区大地构造背景具有重要的指示意义。哲斯组50颗碎屑锆石镜下具有典型岩浆锆石特征,年代学记录表现为4个峰值:(1)(270±2)～(335±4)]Ma,峰期年龄为(272±2)Ma,与该区晚古生代岩浆活动一致;(2)(363±3)～(429±3)]Ma,峰期年龄为(382±4)Ma,暗示其物源来自于松辽地块及其周边地区的加里东期岩浆事件;(3)(507±5)～(555±6)]Ma,峰期年龄为(515±3)Ma,与东北地区各地块的泛非期变质基底年龄一致;(4)少量前寒武纪年龄分别为(847±7)Ma、(923±7)Ma、(1 342±14)Ma、(2 040±13)Ma,表明东北地区存在元古宙的结晶基底。上述碎屑锆石的年代学研究表明,以泛非期和新元古事件年龄为代表,说明研究区哲斯组的物源应来源于东北地区的变质基底,其中年轻一组谐和年龄(270±2)Ma限定了哲斯组的沉积下限为晚二叠世。由于哲斯组的物源均来自于东北地区的变质基底,推测华北和西伯利亚板块的缝合位置在西拉木伦河-长春-延吉一线。

Detrital zircon U-Pb dating from the Permian Zhesi Formation, Suolun area, Eastern Inner Mongolia, China and its tectonic implications

Located in the between of Hegenshan-Heihe fault and Xar Moron River-Changchun-Yanji fault in Inner Mongolia,Suolun exist thick Permian Zhesi Formation,and there is an important significance with instructions to determine the tectonic setting for the Chronological characteristics of Zhesi Formation.50 detrital zircon geochronology study of Zhesi Formation displays four peaks with typical features of magmatic zircons:（1）（270±2）^335±4] Ma with the peak age at（272±2） Ma being identical with Late Paleozoic magmatism;（2）（363±3）^429±3] Ma with the peak age at（382±4） Ma showing that the provenance comes from Caledonian magmatic events of Songliao Block and its surrounding areas;（3）（507±5）^555±6] Ma with the peak age at（515±3） Ma corresponding to Pan-African age of the metamorphic basement in the Northeast China Block;（4）（847±7） Ma,（923±7） Ma,（1 342±14） Ma,（2 040±13） Ma in Precambrian showing that there is Proterozoic crystalline basement in the Northeast China Block.On behalf of the age of Pan-African event,above-mentioned detrital zircon geochronology study shows that the provenance of Zhesi Formation should come from metamorphic basement of the the Northeast China Block in the study area,and the young concordia age is（270±2） Ma which shows that the deposition of lower age should be Late Permian.Because the provenance of Zhesi Formation comes from metamorphic basement of the Northeast China Block,so the suture zone between the Siberia Plate and North China Plate may be the Xar Moron River-Changchun-Yanji fault.