库鲁克塔格位于南天山和塔里木盆地接合部,保留相对较完整的地层记录.其中新元古代贝义西组为一套火山-沉积组合序列,长期以来被认为是Rodinia裂解产物.本文通过对该套组合中的沉积岩(主要是细碎屑岩)地球化学分析,并对该套组合的物源区特征和形成构造环境进行研究,结果并不支持这一结论.研究结果表明,贝义西组砂岩主要为成熟度较低的硬砂岩和岩屑砂屑岩,SiO2为68.58％ ～ 72.97％,K2O/Na2O比值低(0.58～1.13),(Fe2OT+ MgO)为4.01％～7.50％.稀土元素标准化配分曲线呈现轻稀土富集、重稀土平坦和弱Eu、Ce负异常特征.砂岩风化蚀变指数为46 ～ 50,Th/U比值为4.10 ～6.15,表明砂岩物源区经历了相对较弱的风化作用.Zr/Sc和Th/Sc比值共同表明贝义西组的碎屑组成不具备“沉积再旋回”的特征,说明其为近源沉积,具有较差的分选性.砂岩物源区组成判别图研究表明,贝义西组砂岩的物源区主要出露长英质火山岩.古水流资料表明该物源区位于北侧.砂岩形成构造环境判别图解及特征指数分析表明,贝义西组主要形成于大陆岛弧相关沉积盆地.结合前人的研究资料,我们认为贝义西组为弧间盆地充填物.%Quruqtagh area is situated in the linkage of South Tianshan and Tarim basin where well preserved sedimentary records. The Beiyixi Formation in Quruqtagh area is a volcanic-sedimentary succession which were related to breakup of Rodinia supercontinent Our study don' t support the hypothesis based on the geochemical composition of the Neoproterozoic Beiyixi Formation sandstones. Chemical classification of the Beiyixi Formation sandstones indicates that the analyzed sediments are unstable wackes and litharenite. The sandstones are characterized by moderate SiO2 contents (68. 58% -72. 97% ) and low K2O/Na2O ratio (generally 0. 58 ～ 1. 13) and moderate Fe2OT3 + MgO contents (4.01% ～7. 50% ). The REE patterns are characterized by LREE enrichment, flat HREE, and poor negative Eu- and Ce-anomalies. CIA index (generally 46 ～50) and Th/U ratio (4. 10 -6. 15) suggest that these sediments were derived from source rocks with low-moderate weathering. And Zr/Sc and Th/Sc ratios illustrate that all sediments have undergone moderate degree of weathering and no significant sediment recycling, which indicates proximal provenances and poor sorting. Various diagrams for sedimentary provenance using major and trace elements show all the sediments studied were derived predominantly from felsic volcanic rocks source. Sediments were demonstrated to have come mainly from the north areas as indicated by restored paleo-current directions. Geochemical data for these rocks suggest a continental island arc setting. Together with regional geological evidence, the metasediments were deposited in an intra-arc basin.
展开▼
