科研之友
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摘要
The southwestern margin of the Yangtze Block is occupied by the thick volcanic-sedimentary rocks of the Yanbian Group, which is of significance in reconstructing the Neoproterozoic tectonic environment of this region. The elastic sedimentary rocks of the Yanbian Group have been studied on petrology, elastic composition and geochemistry. In addition, two sandstone samples are collected from the Xiaoping Formation and Zhagu Formation, respectively, for zircon U-Pb dating and Hf isotope analysis. In the metasandstone of the Yanbian Group many volcanic lithoclasts and mineral debris of quartz and feldspar have been discerned, which show poor sorting and roundness. In the elastic sedimentary rocks, Al2O3/SiO2 is ranging from 0.12 to 0.4, and K2O/Na2O from 0.14 to 9.45, in which most slates with K2O/Na2O ratio over 1.0, while most sandstones less than 1.0. The LREEs and HREEs in the elastic sedimentary rocks are slightly to moderately differentiated with (La/Yb)(N) ratios from 1.6 to 9.37 and most with substantial negative Eu anomaly. The epsilon(Nd) (t) gives the range of -1.77 to +5.01. The detrital zircons U-Pb result is mainly concentrated at 900Ma to 910Ma with minor ages of Archean to Paleoproterozoic. The weighted mean ages of the young detrital zircons of the Xiaoping and Zhagu formations are 888 +/- 8Ma and 884 +/- 14Ma, respectively. The elastic composition, geochemistry and zircon U-Pb ages all indicate that elastic sediments in the Yanbian Group are proximal deposits, and the sedimentary provenances are from intermediate-felsic volcanic rocks and granites in island arc environment. Combining with the results of the Guandaoshan diorite and the basalt in the Huangtian Fm., the age of the Yanbian Group is constrained to 880 similar to 830Ma, deposited in the back-arc basin environment. Provenance of the elastic sediments is from the volcanic arc at the western margin of the Yangtze Block when the Cathaysian Block was being subducted beneath the Yangtze Block.
- 出版日期2013-2
- 单位中国地质科学院; 中国科学院地质与地球物理研究所; 中国科学院地质与地球物理研究所兰州油气资源研究中心
