桌子山地区奥陶系乌拉力克组碎屑岩地球化学特征及其对物源的制约  

Geochemistry of Ordovician Detrital Rocks and Its Constrains on Provenance in Zhuozishan Area,Northwest Ordos Basin

作　　者：吴素娟[1] 张永生[1] 邢恩袁[1] 

机构地区：[1]国土资源部盐湖资源与环境重点实验室,中国地质科学院矿产资源研究所,北京100037

出　　处：《地质学报》2016年第8期1860-1873,共14页Acta Geologica Sinica

基　　金：中国地质调查局地调工作项目(编号1212011085516);国家重点基础研究发展计划(973计划)项目(编号:2011CB403001)资助的成果

摘　　要：子山地区位于鄂尔多斯盆地西缘北段，保留相对完整的奥陶统地层。本文通过对该地区中-上奥陶统乌拉力克组16件碎屑岩样品进行地球化学分析，对碎屑岩的源区特征和形成构造环境进行了研究。结果表明：乌拉力克组碎屑岩主要为成熟度较低的岩屑砂屑岩，SiO2 为 62.74%～85.47% ， K2O/Na2O比值为2.2～12.9，tFe2O3＋MgO值为2.6%～7.21%。稀土元素标准化配分曲线呈现轻稀土富集、 重稀土平坦和 Eu、 Ce 负异常特征。砂岩风化蚀变指数（CIA）为 66～75，反映温暖、湿润条件下中等的化学风化程度。Zr /Sc 和 Th /Sc 比值共同表明乌拉力克组的碎屑组成不具备“沉积再旋回” 的特征。砂岩物源区组成判别图研究表明，乌拉力克组碎屑岩的物源区主要出露长英质沉积岩。砂岩形成构造环境判别图解及特征指数分析表明，乌拉力克主要形成于大陆岛弧和活动大陆边缘相关沉积盆地，具有多物源的特征。Zhuozi Mountain area is situated in the west northern margin of Ordos Basin where well preserved sedimentary records of Ordovician. Based on an analysis of the testing result of 16 clastic rock samples, this paper systemically discuss the geochemical charateristics and its geological significance. Chemical classification of the Wulalike Formation clasolite indicates that the analyzed sediments are unstable litharenite. The sandstones are characterized by moderate SiO2 contents （he sandstones are characterized by moderate SiO2 contents （ 68. 58%～72. 97% ） and K2O/Na2O ratio （ generally 2.2～12.9）and moderate tFe2O3 ＋ MgO contents （2.6%～7.21%） . The REE patterns are characterized by LREE enrichment, flat HREE,and poor negative Eu-and Ce-anomalies. CIA index （ generally 66～75） suggest that these sediments were derived from source rocks with moderate chemical weathering. And Zr /Sc and Th /Sc ratios illustrate that all sediments have undergone moderate degree of weathering and no significant sediment recycling. Various diagrams for sedimentary provenance using major and trace elements show all the sediments studied were derived predominantly from felsic sedimentary rocks source. Sediments were demonstrated to have come mainly from the south-west areas as indicated by restored paleocurrent directions. Geochemical data for these rocks suggest continental island arc and active continental margin settings. Together with regional geological evidence,the provenance of Wulalike Formation could be mainly the North Qilian orogenic belt and the Alxa Block.

关 键 词：鄂尔多斯盆地 桌子山地区 乌拉力克组 物源 构造环境 

分 类 号：P534.42[天文地球—古生物学与地层学] P588.21[天文地球—地质学]