朝鲜平南盆地祥原超群的沉积时代与拉伸纪早期碳同位素负漂移

Deposition age of the Sangwon Supergroup in the Pyongnam basin( Korea ) and the Early Tonian negative carbon isotope interval

朝鲜平南盆地与东华北克拉通(中朝克拉通)中新元古代盆地的对比存在争议,准确厘定相关沉积建造的沉积时限是解决这些争议的关键。朝鲜平南盆地的地层主体为祥原超群,从下往上依次为直岘群、祠堂隅群、默川群、灭恶山群和燕滩群。直岘群是祥原超群的最下部层位,大部分由陆源碎屑岩组成。从平南盆地"北部型"和"南部型"直岘群碎屑岩中分选锆石,测得LA-ICP-MS U-Pb年龄,限定祥原超群沉积时代晚于1100Ma,并且得出所谓的"北部型"和"南部型"地层没有时代和物源差异。鉴于默川群的基性岩床时代为~900Ma,祥原超群的沉积时代为新元古代早期(1000~900Ma),燕滩群的时代可能稍晚。这说明平南盆地与华北徐淮盆地和旅大盆地等同时。祥原超群碳酸盐岩样品的δ^(13)C值数据表明,默川群时期碳同位素发生了负漂移(δ^(13)C值为-6‰^-5‰)。鉴于侵入到默川群的基性岩床的时代为~900Ma,我们认为该碳同位素(δ^(13)C值)负漂移略早于~900Ma,可能与同一时期的岩浆活动有关。

The relationship of the Pyongnam basin with other basins in the Eastern North China Craton（ Sino-Korean Craton） is in debating; and the deposition age is one key to solve this. The strata in the Pyongnam basin are mainly composed of the Sangwon Supergroup,which comprises the Jikhyon Group,the Sadangu Group,the Muckchon Group,the Myoransan Group and the Yontan Group from bottom to up. The Jikhyon Group is the lowermost formation and comprises of mainly terrestrial clastic sediments. Detrital zircons were separated from the clastic rocks of the Jikhyon Group of both the ‘north-type＇and ‘south-type＇strata of the Pyongnam basin,and their LA-ICP-MS U-Pb ages constrain the maximum deposition age to be 1100 Ma. It further suggests that there are no differences either in deposition age or provenance between the so-called‘north-type＇and‘south-type＇strata. As the mafic sills in the Muckchon Group were intruded at - 900 Ma,we suggest that the majority of the Sangwon Supergroup was deposited at 1000 - 900 Ma,with the Yontan Group to be slightly younger. This indicates that the Pyongnam basin is contemporary with those in the Xu-Huai and Lv-Da basins. The variation of δ-（13）C values of the carbonate samples from the Sangwon Supergroup shows a distinct negative drifting（ δ-（13）C value as low as- 6‰ -- 5‰） in the Mukchon Group. As the mafic sills in the Mukchon Group were emplaced at - 900 Ma,we suggest that this negative drifting of δ-（13）C values happened slightly older than - 900 Ma,and is possibly related to a coeval magmatic event.