扬子克拉通北缘神农架群碳、氧同位素特征及其对古环境和沉积时代的制约  

Characteristics of C and O Isotopes of the Shennongjia Group in the Northern Margin of the Yangtze Craton and their Constraints on Paleoenvironment and Depositional Age

作　　者：田辉[1] 李怀坤[1] 刘欢 张健[1] 周红英[1] 张阔 相振群[1] 瞿乐生 王志先 TIAN Hui;LI Huaikun;LIU Huan;ZHANG Jian;ZHOU Hongying;ZHANG Kuo;XIANG Zhenqun;QU Lesheng;WANG Zhixian(Tianjin Center ,China Geological Survey,Tianjin,300170;Hubei Institute of Regional Geology and Mineral Resources Survey,Wuhan,430034;Administration of Shennongjia National Park,Muyu,Hubei,442421)

机构地区：[1]中国地质调查局天津地质调查中心,天津300170 [2]湖北省区域地质矿产调查所,武汉430034 [3]神农架国家公园管理局,湖北木鱼442421

出　　处：《地质学报》2018年第12期2508-2533,共26页Acta Geologica Sinica

基　　金：中国地质调查局项目(编号121201102000150009-06);湖北省国土资源厅项目<神农架群岩石地层序列和年代格架研究>共同资助成果

摘　　要：对扬子克拉通北缘神农架地区神农架群(1.4～1.0Ga)鹰窝洞组-石槽河组碳酸盐岩进行了系统的碳、氧同位素研究,共获得有效碳、氧同位素数据912组。神农架群岩石学特征、碳氧同位素组成特征对沉积环境具有良好的协同指示意义:神农架群δ13 CV-PDB变化范围-2.20‰～+6.27‰,平均值为+0.93‰;δ18 OV-PDB变化范围-9.95‰～-1.17‰,平均值为-4.95‰;总体属于环潮坪碳酸盐台地-台地边缘-台地前缘斜坡沉积。海水的相对深水期为大岩坪期,相对浅水期为乱石沟期和石槽河期。神农架群δ13 CV-PDB主体变化范围-1.50‰～+5.00‰,下亚群变化范围大于上亚群,整体与华北克拉通北缘蓟县剖面中元古代地层的碳同位素特征差异较大。神农架群和蓟县中元古代地层可能分别对应南乌拉尔地区的中里菲系和下里菲系。通过与全球相关地层碳同位素演化曲线对比,神农架群下亚群最大沉积时限应该小于～1350Ma。神农架群上亚群与北美Bylot超群、西非Atar超群的δ13 CV-PDB变化范围和趋势较为相似,均出现了介于1.2～1.1Ga之间的碳同位素迅速负偏,可能是对Rodinia超大陆汇聚事件的响应。A systematic study of C and O isotopic compositions was conducted for the Shennongjia Group (1.4~1.0 Ga) in the northern margin of the Yangtze Craton, yielding a total of 912 valid data of C and O isotopic compositions. The lithological characteristics and C and O isotopic compositions of the Shennongjia Group are of the important significance for understanding the sedimentary environment. The δ^13CV- PDB of the Shennongjia Group varies from -2.20 ‰ to +6.27 ‰ with an average of +0.93‰ and The δ^18OV- PDB ranges from -9.95 ‰ to --1.17 ‰ with an average of -4.95 ‰, which suggests that the Shennongjia Group can be generally attributed to facies of carbonate platform, platform margin and front platform slope surrounding tidal flat. Correspondingly, the relatively deep water period might occur in the Dayanping period, while the shallowest in the Luanshigou and Shicaohe periods. The δ^13CV- PDB of the Shennongjia Group ranges primarily from -1.50‰ to +5.00‰, among which the lower subgroup has a broader shift range than that of the upper subgroup. The Shennongjia Group differ significantly from the Mesoproterozoic strata of the Jixian Section in the northern margin of the North China Craton in terms of C isotopic composition; both of them might be the counterparts of the Middle Riphean and Lower Riphean in the Southern Ural respectively. Comparison between Shennongjia Group and global C isotopic evolution curve indicates that the maximum depositional age of the lower subgroups of the Shennongjia Group should be less than ~1350 Ma. The upper subgroup of the Shennongjia Group are similar to the Bylot Supergroup of North American and the Atar Supergroup of West African in δ^13C fluctuation range and trend that has an abrupt negative δ^13CV- PDB excursion between 1.2 Ga and 1.1 Ga, which may be a response to the assembly event of the Rodinia supercontinent.

关 键 词：神农架群 中元古代 碳酸盐岩 碳、氧同位素 沉积环境 

分 类 号：P597[天文地球—地球化学] P512.2[天文地球—地质学]