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    赣中新元古代地层地质年代学研究

    Geochronology of the Neoproterozoic strata in central Jiangxi Province

    • 摘要: 华南新元古代地层记录了全球冰川事件、Rodinia超大陆裂解及早期生命演化的重要信息,但其沉积时代和区域地层对比仍存在争议。文章以赣中地区新元古代神山组和上施组为研究对象,通过火山凝灰岩锆石LA-ICP-MS U-Pb定年进一步限定了这两个地层单元的沉积时代,并进行了区域地层对比。研究显示,神山组中部凝灰岩锆石206Pb/238U加权平均年龄为(805 ± 6)Ma,据此将神山组中部沉积年龄限定在ca. 830~800 Ma;上施组中下部凝灰岩锆石206Pb/238U加权平均年龄为(769 ± 6)Ma,对应的沉积年龄限定为770~720 Ma。此外,通过与区域地层年龄对比发现神山组可与扬子地区下江群甲路组((815 ± 6)Ma)、沧水铺组((821 ± 13)Ma)、丹洲群合桐组((801 ± 4)Ma)、五强溪组((809 ± 9) Ma)以及番召组((802 ± 2)Ma)建立等时地层格架;上施组与河上镇群上墅组((767 ± 5)Ma)、清水江组((764 ± 6)Ma)以及莲沱组((763 ± 10)Ma、(767 ± 3)Ma)存在良好的年代学对应关系。此次研究为扬子/华夏地块新元古代地层对比进一步提供了年代学证据。

       

      Abstract: The Neoproterozoic stratigraphy of South China records important information about global glacial events, the Rodinia supercontinent rifting, and early life evolution. However, its depositional age and regional stratigraphic comparison remain controversial. This study focuses on the geochronology of Neoproterozoic Shenshan and Shangshi Formations in the central Jiangxi of South China by means of zircon LA-ICP-MS U-Pb dating on tuffaceous siltstone to constrain the depositional age of these stratigraphic units and facilitate their regional stratigraphic correlation. The study shows that zircon 206Pb/238U weighted mean ages of (805 ± 6) Ma was obtained from tuffaceous siltstone layers in the middle Shenshan Formation, which limits the depositional age of the central Shenshan Formation at ca. 830~800 Ma,while that in the middle and lower Formation is (769 ± 6) Ma, corresponding to the depositional age of ca. 770~720 Ma. Furthermore, the comparison of these isotopic ages indicate an isochronal stratigraphic framework between the Shenshan Formation and the Jialu Formation ((815 ± 6 ) Ma) and the Cangshuipu Formation((821 ± 13) Ma)of the Xiajiang Group, the Hetong Formation((801 ± 4) Ma), Wuqiangxi Formation ((809 ± 9)Ma) and the Panzhao Formation ((802 ± 2) Ma)of the Danzhou Group in the Yangtze Block. The Shangshi Formation geochronologically corresponds with the Shangshu Formation ((767 ± 5) Ma) of the Heshangzhen Group, the Qingshuijiang Formation ((764 ± 6) Ma), and the Liantuo Formation ((763 ± 10) Ma ~ (767 ± 3) Ma) in the Yangtze Block. This study provides additional geochronological evidence for the correlation of Neoproterozoic strata between the Yangtze and Cathaysia blocks.

       

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