淮南地区中——新元古界LA-ICP-MS碎屑锆石U-Pb年龄及地质意义

THE CHARACTERISTICS OF LA-ICP-MS DETRITAL ZIRCON U-PB AGE FROM THE MESO-NEOPROTEROZOIC STRATA IN HUAINAN AREA AND THEIR GEOLOGICAL SIGNIFICANCE

淮南地区中—新元古代地层保存有大量精美的宏体碳质压膜化石和有机质壁微体化石,是新元古代大冰期之前生命演化的重要实证材料。然而,淮南地区中—新元古代地层的沉积时间仍未得到较好的约束,碎屑锆石年龄随地层层序的变化特征也未明确。为此本文对碎屑锆石数据较少的淮南寿县地区中—新元古代地层开展了系统的碎屑锆石U-Pb同位素测年。结果显示,八公山组碎屑锆石以古元古代锆石为主体,无小于1600 Ma的锆石;刘老碑组和寿县组碎屑锆石以中元古代锆石为主体,中元古代之前的锆石较少。综合已知的碎屑锆石年龄以及与邻区地层的对比,约束寿县组沉积时间为~950—~945 Ma,刘老碑组沉积时间为~1110—~945 Ma。淮南与鲁西地区中—新元古代地层的碎屑锆石年龄谱、沉积序列、沉积环境和化石产出相似,两地地层可相互对比。淮南地区中元古代早期及之前的碎屑锆石源区可能在华北克拉通东部,而中元古代晚期的碎屑锆石的源区则可能不在华北克拉通。

The Meso-Neoproterozoic strata in the Huainan area delicately preserves a large number of carbonaceous compression macrofossils and organic-walled microfossils,which are valuable materials for providing insights into the evolution of pre-Cryogenian life.However,the depositional time of the Meso-Neoproterozoic strata in the Huainan area has not been well constrained,and the distribution characteristics of detrital zircon age along with stratigraphic sequence are still unclear.In this study,detrital zircon U-Pb isotopic dating of Meso-Neoproterozoic strata has been carried out systematically in Shouxian,Huainan area,where data of detrital zircon age is limited.The results show that detrital zircons from the Bagongshan Formation are mainly Paleoproterozoic in age and none of them are younger than 1600 Ma;whereas detrital zircons from the Liulaobei and Shouxian formations are mainly Mesoproterozoic in age with a few of them older than Mesoproterozoic.Based on this study and previously published geochronological data,as well as the correlation with strata in adjacent areas,the depositional time of the Shouxian Formation is between~950 Ma–~945 Ma,and that of the Liulaobei Formation is between~1110 Ma–~945 Ma.The detrital zircon age distribution,sedimentary sequence,sedimentary environment and fossil occurrences of the Meso-Neoproterozoic strata in Huainan and western Shandong are comparable,and the strata in the two areas can be well-correlated.The detrital zircons of early Mesoproterozoic and pre-Mesoproterozoic in age from the Meso-Neoproterozoic strata in the Huainan area may be from the eastern North China Craton,whereas the detrital zircons of late Mesoproterozoic in age may not be from the North China Craton.