THE U-Pb CHRONOLOGICAL EVIDENCE FOR THE VOLCANIC ROCKS OF TANGJIATUN FORMATION IN EAST HARBIN, HEILONGJIANG PROVINCE
WANG Xing1, ZHENG Tao1, GU Hua-juan1, NIU Yan-hong1, LIANG Cheng-zhe2
1. Qiqihar Branch, Heilongjiang Institute of Geological Survey, Qiqihar 161005, Heilongjiang Province, China; 2. China University of Geosciences, Beijing 100083, China
Abstract：The Tangjiatun Formation, dominated by strong schisteous acidic and acidic-intermediate volcanic rocks, with minor intermediate volcanic rocks and metamorphosed normal sedimentary rocks, are widely exposed in East Harbin, Heilongjiang province. The volcanic rocks contain SiO2 of 61.50%-68.96%, TiO2 of 0.61%-0.88%, Fe2O3 of 1.21%-4.24%, MgO of 0.30%-2.08% and CaO of 0.77%-4.57%, with Mg# of 4-25, Al2O3=15.12%-16.99%, K2O=2.68%-5.2%. The alkaline content is rich, with Na2O/K2O=0.94-2.18, Na2O + K2O=7.05%-9.99%. The total REE contents are 140.81×10-6-276.36×10-6, with LREE/HREE ratio of 7.72-9.70. The rocks are enriched in LREE but depleted in HREE, with δEu=0.77-1.03, i.e. negative anomaly to slightly positive anomaly. The mode of REE patterns shows right-inclined curves. The trace elements of the rocks are rich with LILEs (Zr and Ba) and depleted with HFSEs (Nb, Ta and Ti), Sr and P, showing the characteristics of bimodal volcanic rocks. The LA-ICP-MS U-Pb dating result of the volcanic rocks yields the weighted average age of 300±1 Ma, indicating the forming age of Late Carboniferous Epoch, which was an extensional environment.
2016, Vol. 25 
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