湖北峡东地区奥陶系南津关组灰岩中硅质岩地球化学特征及其沉积环境意义  

Geochemistry Characteristics of Cherts from Ordovician Nanjinguan Formation Limestone in the Eastern Yangtze Gorges Area of Hubei,China and Their Implications for Sedimentary Environment

作　　者：周北昱 李盼 曾雯[1] 曾薇 汪蕾 刘越 刘影 ZHOU Bei-yu;LI Pan;ZENG Wen;ZENG Wei;WANG Lei;LIU Yue;LIU Ying(Three Gorges Research Center for Geohazards of Ministry of Education,China University of Geosciences,Wuhan 430074,Hubei,China;School of Earth Sciences,China University of Geosciences,Wuhan 430074,Hubei,China)

机构地区：[1]中国地质大学(武汉)教育部长江三峡库区地质灾害研究中心,湖北武汉430074 [2]中国地质大学(武汉)地球科学学院,湖北武汉430074

出　　处：《地球科学与环境学报》2020年第4期464-478,共15页Journal of Earth Sciences and Environment

基　　金：中国地质调查局地质调查项目(12120113061900)。

摘　　要：湖北峡东地区位于华南板块上扬子地块分区,其奥陶系南津关组灰岩中发育大量条带状和结核状硅质岩。在详细野外调查的基础上,对这些硅质岩进行岩相学和地球化学分析,探讨其成因及沉积环境意义。结果表明:硅质岩主要由石英、玉髓组成;硅质岩贫Mn、Fe,其A1/(Al+Fe+Mn)值为0.27~0.84,平均值为0.64,Mn/TiO2值小于0.5,Th/U值为0.02~0.86;硅质岩具有低的稀土元素含量(质量分数,下同),稀土元素总含量为(0.67~27.79)×10^-6,经北美页岩标准化后呈现相对平缓右倾的稀土元素配分模式和弱的Ce异常,同时(La/Yb)N平均值为1.31;硅质岩寄主灰岩的δ^13 C值为-2.37‰~2.30‰,平均值为-0.0064‰,δ^18 O值为-9.04‰^-6.49‰,平均值为-7.61‰,计算的古环境温度为4℃~21℃。这些结果反映湖北峡东地区奥陶系南津关组灰岩中的硅质岩主要为生物成因,形成于温暖缺氧的大陆边缘环境。The eastern Yangtze Gorges area in Hubei belongs to the Upper Yangtze block of South China plate.The cherts from Ordovician Nanjinguan Formation limestone in this area are mostly developed as nodules and strips.Based on the detailed field geological survey,the petrography and geochemistry characteristics of these cherts were analysed,and the genesis and sedimentary environment were discussed.The results show that the main mineral compositions of cherts are quartz and chalcedony.Cherts are poor in Mn and Fe,the ratios of A1/(Al+Fe+Mn)range from 0.27 to 0.84 with an average of 0.64,which is closer to that of the biogenic cherts.The ratio of MnO/TiO2 is much less than 0.5,indicating cherts in this area form in the shallow sea sedimentary environment near the edge of the land.The ratios of Th/U range from 0.02 to 0.86 with an average of 0.24.Cherts have low REE content,the total REE content is(0.67-27.79)×10^-6.The NASC-normalized REE pattern shows a relatively gentle right-leaning trend.TheδCe ranges from 0.97 to 1.19 with an average of 1.11,and the average value of(La/Yb)N is 1.31,reflecting a bio-chemical origin rather than hydrothermal origin,and cherts form in a setting of continental margin.The carbon and oxygen isotope information of the host limestone of cherts in Nanjinguan Formation shows that theδ^13 C ranges from-2.37‰to 2.30‰with an average of-0.0064‰,theδ^18 O ranges from-9.04‰to-6.49‰with an average of-7.61‰.The paleoenvironmental temperature varies from 4℃to 21℃.The geochemistry characteristics of cherts in Nanjinguan Formation limestone indicate that cherts are biogenic origin and form in a warm and anoxic continental marginal tectonic settings.

关 键 词：沉积环境 岩石成因 硅质岩 灰岩 地球化学 奥陶系 南津关组 湖北 

分 类 号：P595[天文地球—地球化学]