Tectonic background and deposition epoch of the Tongshan Formation in Wayao area of Dong Ujimqin Banner, Inner Mongolia
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摘要:
铜山组作为内蒙古北疆兴安地层区早古生代的沉积记录,其沉积环境、成岩时代及构造环境的研究是认识兴蒙造山系早期构造演化的理想窗口。对出露于内蒙古东乌旗瓦窑地区的奥陶纪铜山组进行沉积序列、沉积相及沉积物特征研究,结果显示铜山组为一套陆源碎屑浊积岩。首次获得铜山组中夹层凝灰岩LA-ICP-MS锆石U-Pb年龄为458.5±2.6Ma,显示其沉积时代为中奥陶世-晚奥陶世早期。碎屑岩地球化学分析揭示,铜山组物源区主要具活动大陆边缘和大陆岛弧特征。结合区域地质资料,推测其为活动大陆边缘环境下浊积扇沉积的产物。
Abstract:The sedimentary environment, deposition epoch and tectonic environment type of Tongshan Formation as well as the early Paleozoic sedimentary records of Xing'an stratigraphic region constitute an important window to study the early stage tectonic evolution of Xing-Meng orogenic belt. The authors studied Ordovician Tongshan Formation exposed in the Wayao area of Dong Ujimqin Banner in Inner Mongolia. Sedimentary sequence, sedimentary facies and features of sediments indicate that Tongshan Formation is terrigenous clastic turbidite. LA-ICP-MS zircon U-Pb dating of volcanic tuff sampled from Tongshan Formation yielded the depositional age of 458.5±2.6Ma for the first time in Inner Mongolia and restricted its age between late Middle Ordovician and early Late Ordovician. Geochemistry of the detrital rocks shows that the tectonic setting of the provenance for the Tongshan Formation is mainly charac-terized by the Active Continental Margin (ACM) and Continental Island Arc (CIA). Combined with the regional geological data, the authors infer that the Tongshan Formation was formed by the turbidite fan in a active continental margin tectonic environment.
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Key words:
- Inner Mongolia /
- Dong Ujimqin Banner /
- Tongshan Formation /
- Ordovician /
- tectonic environment
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图 1 内蒙古中部及邻区构造地质简图(a,据参考文献[4]修改)、内蒙古阿拉坦合力地区奥陶系分布简图(b)和瓦窑地区铜山组地质简图(c)
Figure 1.
图 5 瓦窑铜山组砂岩K2O/Na2O-SiO2/Al2O3构造环境判别图解[30]
Figure 5.
图 6 瓦窑铜山组砂岩微量元素的构造环境判别图[30]
Figure 6.
表 1 铜山组砂岩粒度参数(括号内为图解法)
Table 1. Grain size parameters of sandstones in Tongshan Formation
序号 平均值(Mz) 标准偏差(σ) 偏度(SK) 峰度(K) b0220-1-2 1.93 (1.84) 1.55 (1.34) 1.53 (-0.23) 8.41 (0.99) b0220-4-1 2.70 (2.42) 1.49 (1.40) 2.81 (0.37) 10.77 (3.13) b0220-8-2 1.78 (1.55) 1.72 (1.77) 2.33 (0.23) 9.45 (1.95) b0220-8-3 2.47 (2.25) 1.30 (0.70) 3.20 (0.04) 14.63 (1.03) b0222-12-1 2.24 (1.86) 2.02 (2.01) 1.73 (0.15) 6.09 (2.23) b0222-12-2 1.92 (1.75) 1.25 (0.65) 3.58 (0.09) 18.54 (1.01) 注:江汉油田实验室测试 表 2 瓦窑铜山组英安质晶屑凝灰岩LA-ICP-MS锆石U-Th-Pb同位素数据
Table 2. LA-ICP-MS zircon U-Th-Pb isotope data for dacite volcanic tuffs of Tongshan Formation from Wayao area
分析点号 含量/10-6 Th/U 同位素比值 年龄/Ma Th U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 208Pb/232Th 1σ 206Pb/238U 1σ 207Pb/235U 1σ 1 18 193 0.57 0.0581 0.0009 0.657 0.010 0.0821 0.0007 0.0332 0.0005 509 4 513 8 2 16 174 0.45 0.0607 0.0019 0.680 0.023 0.0812 0.0014 0.0401 0.0017 504 9 527 18 3 61 810 0.27 0.0567 0.0006 0.581 0.006 0.0743 0.0011 0.0305 0.0002 462 7 465 5 4 60 772 0.36 0.0581 0.0007 0.590 0.008 0.0736 0.0007 0.0325 0.0010 458 5 471 6 5 67 785 0.36 0.0577 0.0005 0.654 0.006 0.0821 0.0007 0.0340 0.0010 509 4 511 5 6 23 258 0.80 0.0587 0.0012 0.594 0.014 0.0735 0.0008 0.0330 0.0004 457 5 473 11 7 62 835 0.24 0.0546 0.0006 0.556 0.006 0.0738 0.0008 0.0319 0.0003 459 5 449 5 8 53 599 0.28 0.0613 0.0007 0.709 0.009 0.0839 0.0008 0.0474 0.0011 519 5 544 7 9 52 686 0.26 0.0562 0.0006 0.580 0.006 0.0748 0.0009 0.0329 0.0002 465 5 465 5 10 48 592 0.48 0.0587 0.0013 0.590 0.016 0.0729 0.0011 0.0343 0.0005 453 7 471 12 11 41 485 0.25 0.0562 0.0026 0.630 0.033 0.0814 0.0010 0.0453 0.0022 504 6 496 26 12 108 808 0.97 0.0596 0.0025 0.689 0.036 0.0838 0.0008 0.0677 0.0006 519 5 532 28 13 52 545 0.51 0.0598 0.0012 0.684 0.014 0.0830 0.0011 0.0448 0.0015 514 7 529 11 14 16 189 0.66 0.0555 0.0018 0.571 0.020 0.0747 0.0008 0.0296 0.0005 464 5 459 16 15 23 269 0.60 0.0602 0.0012 0.601 0.013 0.0724 0.0006 0.0342 0.0006 450 4 478 10 16 22 205 0.59 0.1185 0.0041 1.524 0.058 0.0933 0.0013 0.0361 0.0010 575 8 940 35 17 32 343 0.47 0.0623 0.0026 0.700 0.035 0.0814 0.0012 0.0435 0.0010 504 8 538 27 18 29 196 0.74 0.0602 0.0009 0.672 0.012 0.0809 0.0009 0.0315 0.0003 502 6 522 9 19 92 196 0.67 0.0692 0.0010 0.884 0.017 0.0926 0.0011 0.0374 0.0010 571 7 643 12 20 49 193 0.39 0.0670 0.0007 0.687 0.009 0.0743 0.0010 0.0299 0.0006 462 6 531 7 21 68 174 0.40 0.0642 0.0006 0.659 0.007 0.0744 0.0010 0.0375 0.0011 463 6 514 5 22 35 810 0.61 0.0559 0.0010 0.570 0.013 0.0739 0.0011 0.0261 0.0006 460 7 458 10 23 67 187 0.35 0.0605 0.0014 0.618 0.019 0.0741 0.0015 0.0308 0.0006 461 9 488 15 24 22 785 1.31 0.0745 0.0016 0.748 0.018 0.0727 0.0008 0.0294 0.0004 453 5 567 14 25 62 258 0.50 0.0644 0.0013 0.6450 0.015 0.0732 0.0009 0.0348 0.0010 455 6 508 12 26 60 835 0.29 0.0590 0.0007 0.605 0.007 0.0744 0.0007 0.0326 0.0006 462 4 480 5 27 53 599 0.73 0.0572 0.0007 0.642 0.009 0.0815 0.0007 0.0261 0.0004 505 4 504 7 28 80 686 0.35 0.0677 0.0007 1.264 0.013 0.1354 0.0014 0.0490 0.0016 819 8 830 8 29 54 592 0.48 0.0594 0.0006 0.607 0.006 0.0741 0.0012 0.0282 0.0004 461 7 482 4 30 167 242 1.44 0.0908 0.0052 1.048 0.074 0.0837 0.0015 0.0433 0.0016 518 9 728 52 表 3 瓦窑铜山组中砂岩地球化学数据
Table 3. Geochemical data of sandstones from the Tongshan Formation in Wayao area
元素 SiO2 TiO2 AI2O3 Fe2O3 FeO MgO MnO TFe CaO K2O P2O5 Na2O 烧失量 Rb Sr Ba Nb Zr Hf Th Cr Co Ni Sc La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Y V HF0220-1-2 78.29 0.26 9.80 0.51 1.33 0.95 0.05 1.84 2.02 3.65 0.12 2.17 0.85 143.8 161.8 678.8 5.97 156.3 5.19 10.71 25.3 3.62 11.59 4.62 23.16 45.68 5.35 20.69 4.05 0.68 3.87 0.59 3.55 0.7 2.01 0.31 2.01 0.32 19.32 29.83 HF0220-5-2 62.79 0.68 17.34 1.83 4.38 2.94 0.11 6.21 0.36 5.59 0.10 1.18 2.70 233.5 70.25 594.8 14.17 225.9 6.50 14.05 76.2 10.52 52.71 17.44 51.92 98.62 11.74 44.67 8.58 1.21 7.00 1.23 6.96 1.3 3.68 0.59 4.02 0.61 36.50 103.7 HF0220-8-3 77.29 0.25 10.77 0.85 0.90 0.65 0.06 1.75 1.62 4.10 0.10 2.50 0.91 138.2 171.3 795.6 6.48 135.5 4.38 9.58 26.2 3.05 11.42 4.70 26.20 42.64 5.70 20.80 3.97 0.78 3.55 0.59 3.34 0.66 1.95 0.35 2.02 0.30 19.48 28.81 HF0220-9-1 82.50 0.21 8.28 1.59 0.37 0.85 0.10 1.96 3.23 0.52 0.09 1.24 1.02 17.76 307.3 450.3 5.27 120.4 3.92 8.25 25.9 3.16 16.95 3.75 16.07 30.06 3.75 14.60 2.70 0.66 2.51 0.43 2.59 0.55 1.58 0.27 1.68 0.26 14.31 26.89 HF0222-12-2 83.33 0.15 7.99 0.17 0.77 0.39 0.05 0.94 0.85 3.46 0.05 1.70 1.09 75.89 120.0 660.1 8.61 105.6 3.52 7.67 18.4 3.15 11.92 3.94 15.00 29.60 3.41 12.95 2.45 0.62 2.19 0.35 2.19 0.44 1.28 0.20 1.35 0.22 11.53 20.42 注:主量元素含量单位为%,微量和稀土元素含量为10-6 -
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