黑龙江滨东地区唐家屯组火山岩时代的U-Pb年代学证据

黑龙江省滨东地区广泛发育唐家屯组火山岩,其以强片理化酸性、中酸性火山岩为主,夹少量中性火山岩及片理化变质的正常沉积岩.唐家屯组火山岩Si O2含量为61.50%~68.96%,Ti O2、Fe2O3、Mg O和Ca O的含量分别为0.61%~0.88%、1.21%~4.24%、0.30%~2.08%和0.77%~4.57%.Mg#为4~25,Al_2O_3=15.12%~16.99%,K2O=2.68%~5.2%,Na2O/K2O=0.94~2.18,Na2O+K2O=7.05%~9.99%,较富碱.稀土元素总量(∑REE)为140.81×10-6~276.36×10-6,LREE/HREE比值为7.72~9.70,明显富轻稀土元素,贫重稀土元素.δEu=0.77~1.03,具有负异常—弱的正异常,稀土元素配分曲线为右倾性.微量元素总体上富集大离子亲石元素(LILE)Zr、Ba,亏损Nb、Ta、Ti等高场强元素和Sr、P,具有双峰式火山岩的特点.该火山岩LA-ICP-MS U-Pb定年的结果显示,其加权平均年龄分别为300±1 Ma,形成时代为晚石炭世,其形成于引张环境.

THE U-Pb CHRONOLOGICAL EVIDENCE FOR THE VOLCANIC ROCKS OF TANGJIATUN FORMATION IN EAST HARBIN,HEILONGJIANG PROVINCE

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.