LA-ICP-MS zircon U-Pb geochronology and geochemical characteristics of the Early Permian granite in Chifeng area, Inner Mongolia
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摘要:
以赤峰地区铭山复式岩体、尖山子岩体为研究对象,通过锆石U-Pb年龄、地球化学研究,确定了其形成时代,探讨了岩石成因和岩浆源区性质及其形成的构造背景。LA-ICP-MS锆石206Pb/238U测年结果表明,铭山复式岩体中灰白色斑状黑云二长花岗岩、尖山子岩体中浅肉红色细粒正长花岗岩分别形成于284.4±7.9Ma、294.7±8.5Ma,为早二叠世。根据地质体间接触关系可知,铭山复式岩体中的二长花岗岩岩体和尖山子岩体均为复式岩体,有待进一步解体。斑状黑云二长花岗岩SiO2含量较高,K2O+Na2O含量较高,A/CNK < 1,属于高钾钙碱性I型花岗岩。细粒正长花岗岩Al2O3含量为14.32%~15.14%,Na2O/K2O=0.71~0.99,A/CNK=1.17~1.20,在标准矿物中出现刚玉分子。二者微量元素特征相似,富集大离子亲石元素,亏损高场强元素Nb、Ta,具Sr、P、Ti的负异常,表现出岛弧岩浆岩类特征。结合岩石地球化学、区域地质特征,认为赤峰地区早二叠世岩体形成于岛弧/活动大陆边缘构造背景,其形成与古亚洲洋向南俯冲有关。
Abstract:In this paper, the authors studied the geochronology and geochemistry of the Mingshan granitic complex and Jianshanzi granite in Chifeng area, with the purpose of providing constraints on the formation time, petrogenesis and tectonic background on the northern margin of the North China Block. The zircon U-Pb age data obtained by using laser ablation ICP-MS technique are 284.4±7.9Ma and 294.7±8.5Ma, indicating that the Mingshan granitic complex and Jianshanzi granite were formed in Early Permian. The major elements characteristics of the porphyritic biotite monzogranite are high in SiO 2 and (K2O+Na2O), with A/CNK lower than 1, belonging to high K calc-alkaline I-type granite. The syenogranite has Al2O3 14.32%~15.14%, Na2O/K2O 0.71~0.99 and A/CNK 1.17~1.20, with corundum molecule in CIPW standard mineral calculation. The porphyritic biotite monzogranite and syenogranite are similar in trace elements, with enrichment of large ion lithophile elements, loss of high-field strong elements, and obvious negative Sr, P and Ti anomalies, thus having the characteristics of island-arc magma. In combination with the geochemistry and regional geological characteristics, it is suggested that the Early Permian granites in Chifeng area was generated in an island-arc/active continental margin tectonic setting.
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致谢: 样品测试分析得到中国地质调查局沈阳地质调查中心检测分析中心、河北省区域地质调查大队地质实验室、武汉地质调查中心自然资源部中南矿产监督检测中心等单位的大力支持,审稿专家对文稿提供了宝贵的修改意见,在此一并表示诚挚的谢意。
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图 1 研究区地质简图
a—华北克拉通北缘构造纲要图;b—桥头镇北部地质简图④;c—老府镇地区地质简图⑤[14];Q—第四系;N1h—汉诺坝组;J3b—白音高老组;J3mk—满克头鄂博组;K/J—侏罗纪/白垩纪火山岩;K1γ—早白垩世花岗质岩石;K1ξγ—早白垩世正长花岗岩;J3ξγ-晚侏罗世正长花岗岩;T3γο—晚三叠世英云闪长岩;P2ξγ—中二叠世正长花岗岩;P1γ—早二叠世花岗质岩石;P1ηγ—早二叠世二长花岗岩;D3γ—晚三叠世花岗质岩石;D3δ—晚三叠世闪长岩;J3tc—土城子组;J2x—新民组;P2e—额里图组;P1s—三面井组;Pt1by—宝音图群;Ar-太古宙基底。1—流纹岩;2—安山岩;3—玄武安山岩;4—橄榄玄武岩;5—花岗质岩石;6—正长花岗岩;7—二长花岗岩;8—英云闪长岩;9—闪长岩;10—基性岩;11—采样点;12—太古宙基底;13—元古宙地层;14—酒局子组;15—断层
Figure 1. Simplified geological map of the study area
图 5 二长花岗岩(14CH24)和正长花岗岩(14CH10)TAS(a)和SiO2-K2O图解(b)
1—橄榄辉长岩;2a—碱性辉长岩;2b—亚碱性辉长岩;3—辉长闪长岩;4—闪长岩;5—花岗闪长岩;6—花岗岩;7—硅英岩;8—二长辉长岩;9—二长闪长岩;10—二长岩;11—石英二长岩;12—正长岩;13—副长石辉长岩;14—似长石二长闪长岩;15—似长石二长正长岩;16—似长石正长岩;17—似长石深成岩
Figure 5. SiO2-(K2O+Na2O)(a) and SiO2-K2O (b) patterns of monzogranite (14CH24) and syenogranite (14CH10)
图 8 二长花岗岩(14CH24)和正长花岗岩(14CH10)Ta/Yb-Th/Yb图解[29]
Figure 8. Ta/Yb-Th/Yb patterns of monzogranite (14CH24) and syenogranite (14CH10)
表 1 样品LA-ICP-MS锆石U-Th-Pb分析结果
Table 1 LA-ICP-MS zircon U-Th-Pb data of samples
测点编号 U Th Pb Th/U 同位素比值 年龄/Ma 10-6 207Pb/206Pb ±1σ 207Pb/235U ±1σ 206Pb/238U ±1σ 206Pb/238U ±1σ 正长花岗岩(14CH10) 01* 332.72 212.94 25.37 0.64 0.067 0.003 0.422 0.020 0.046 0.001 288 7 02 184.13 90.22 12.21 0.49 0.049 0.003 0.333 0.020 0.048 0.002 304 9 03 254.02 317.53 16.26 1.25 0.050 0.002 0.309 0.010 0.045 0.001 285 7 04 116.36 61.67 14.35 0.53 0.056 0.003 0.350 0.018 0.046 0.002 293 10 05 452.98 231.02 28.85 0.51 0.056 0.003 0.362 0.020 0.049 0.002 306 12 06 280.38 126.17 19.96 0.45 0.054 0.002 0.363 0.020 0.050 0.002 313 11 07* 116.91 53.78 37.30 0.46 0.056 0.003 0.347 0.018 0.045 0.001 286 9 08* 763.71 404.77 51.73 0.53 0.069 0.006 0.436 0.030 0.052 0.003 326 15 09 159.26 71.67 14.58 0.45 0.053 0.002 0.331 0.014 0.045 0.001 285 8 10 467.06 298.92 26.27 0.64 0.054 0.002 0.351 0.015 0.048 0.002 301 10 11 265.70 127.53 16.68 0.48 0.051 0.002 0.356 0.022 0.051 0.002 319 12 12* 264.24 224.60 10.27 0.85 0.060 0.003 0.349 0.016 0.045 0.002 280 11 13* 145.35 68.32 18.60 0.47 0.061 0.003 0.427 0.022 0.052 0.002 324 12 14 237.81 99.88 13.62 0.42 0.053 0.002 0.369 0.019 0.051 0.002 318 10 15 256.28 107.64 22.85 0.42 0.053 0.003 0.358 0.022 0.049 0.002 309 11 16* 458.85 142.24 28.63 0.31 0.063 0.003 0.386 0.019 0.045 0.001 285 6 17* 372.73 197.55 50.37 0.53 0.034 0.002 0.240 0.017 0.051 0.002 320 10 18* 302.52 166.39 25.71 0.55 0.071 0.004 0.430 0.021 0.044 0.001 279 6 19 282.10 160.80 13.26 0.57 0.052 0.002 0.316 0.014 0.044 0.001 280 5 20 117.45 68.12 19.16 0.58 0.051 0.002 0.330 0.016 0.048 0.001 299 6 二长花岗岩(14CH24) 01 257.82 296.49 15.10 1.15 0.057 0.003 0.338 0.019 0.043 0.001 273 5 02 245.79 196.63 21.64 0.80 0.058 0.003 0.372 0.021 0.048 0.001 300 4 03 175.38 140.30 9.56 0.80 0.064 0.004 0.421 0.023 0.049 0.001 307 5 04* 826.96 512.72 53.77 0.62 0.224 0.013 2.056 0.140 0.059 0.002 370 9 05 174.61 169.37 18.79 0.97 0.051 0.003 0.381 0.020 0.054 0.001 339 5 06 211.53 205.18 28.09 0.97 0.065 0.004 0.384 0.022 0.043 0.001 272 4 07* 201.92 246.34 12.17 1.22 0.074 0.003 0.530 0.028 0.050 0.001 317 6 08* 92.45 65.64 15.86 0.71 0.147 0.018 1.121 0.137 0.053 0.001 332 8 09 252.73 217.35 16.72 0.86 0.079 0.005 0.479 0.027 0.046 0.001 293 7 10* 405.16 320.08 22.32 0.79 0.140 0.013 1.166 0.132 0.053 0.001 331 8 11* 143.52 114.82 16.12 0.80 0.108 0.014 0.586 0.071 0.043 0.001 270 7 12 173.82 161.65 18.06 0.93 0.062 0.004 0.389 0.023 0.046 0.001 293 5 13* 49.27 43.85 17.83 0.89 0.120 0.011 0.785 0.067 0.051 0.002 320 10 14 118.25 100.51 8.35 0.85 0.063 0.004 0.391 0.021 0.045 0.001 284 5 15 217.34 180.39 13.19 0.83 0.069 0.004 0.440 0.028 0.047 0.001 296 5 16 348.89 373.31 23.35 1.07 0.067 0.004 0.415 0.023 0.044 0.001 277 4 17 373.74 370.00 17.62 0.99 0.068 0.004 0.386 0.025 0.042 0.001 264 6 18 86.75 74.61 5.79 0.86 0.065 0.005 0.397 0.027 0.044 0.001 277 7 19 173.91 146.08 8.72 0.84 0.064 0.005 0.404 0.033 0.044 0.001 280 9 注:*为调谐度太大剔除样品 表 2 样品主量、微量和稀土元素分析结果
Table 2 Major, trace and rare earth elements compositions of the sample
样品 14CH10 14CH11 H14C12 H14C23 14CH24 14CH25 14CH26 14CH27 SiO2 71.05 71.44 70.74 71.32 71.42 72.59 71.51 72.02 TiO2 0.36 0.36 0.39 0.40 0.41 0.34 0.41 0.37 Al2O3 14.54 14.32 15.14 14.02 14.04 13.68 13.95 13.77 TFe2O3 2.20 2.33 2.90 2.71 2.70 2.20 2.78 2.48 FeO 1.4 1.11 1.41 1.78 2.34 1.67 2.45 1.53 MnO 0.06 0.06 0.08 0.06 0.06 0.05 0.06 0.05 MgO 0.47 0.47 0.51 0.78 0.76 0.63 0.79 0.68 CaO 0.80 0.64 0.60 2.01 2.02 1.73 2.01 1.81 Na2O 3.46 3.57 4.28 4.21 4.14 3.92 4.08 3.98 K2O 4.87 4.54 4.32 3.74 3.75 4.13 3.68 3.96 P2O5 0.117 0.112 0.12 0.116 0.118 0.096 0.119 0.105 烧失量 2.05 2.05 0.91 0.63 0.57 0.63 0.6 0.76 总计 99.97 99.89 99.99 100.0 99.98 99.99 99.99 99.99 La 37.5 28.3 28.1 41.7 43.6 31.9 45.4 40.8 Ce 71.5 57.2 69.3 74.1 74.5 56.8 78.1 68.7 Pr 7.79 6.05 6.19 7.5 7.48 5.64 8.02 6.99 Nd 27.5 22.3 22.7 25.5 24.5 19.4 26.8 24 Sm 4.62 3.97 4.25 4.07 3.66 3.01 4.09 3.44 Eu 0.901 0.701 0.685 0.872 0.785 0.757 0.833 0.736 Gd 4.66 4.03 4.61 3.88 3.55 2.79 3.67 3.28 Tb 0.596 0.583 0.663 0.52 0.465 0.381 0.523 0.445 Dy 3.25 3.32 3.73 2.54 2.47 2.03 2.54 2.38 Ho 0.688 0.699 0.849 0.604 0.531 0.413 0.545 0.467 Er 1.97 2.06 2.34 1.65 1.49 1.24 1.6 1.37 Tm 0.316 0.351 0.378 0.256 0.211 0.203 0.255 0.24 Yb 2.14 2.37 2.62 1.79 1.62 1.42 1.73 1.51 Lu 0.321 0.356 0.381 0.258 0.207 0.208 0.266 0.248 Y 16.8 18.4 19.7 14.7 12.3 11.1 14.6 12.6 Sc 4.71 4.92 5.14 4.99 4.8 3.6 4.97 4.25 V 18 15.8 19.5 22.5 22.5 19 27.4 20.8 Cr 5.55 6.36 5.98 6.67 5.98 5.53 4.76 8.18 Co 2.19 2.3 2.69 3.59 3.32 2.62 3.64 3.18 Ni 2.13 1.58 1.97 2.34 2.49 2.16 1.52 5.8 Be 1.68 1.68 2.23 2.22 1.53 1.5 1.58 1.85 Rb 151 150 131 98.9 88.9 89.8 89.9 92.6 Sr 170 167 170 265 238 228 258 240 Ba 929 918 748 747 591 783 643 829 Li 25.3 24.6 12 17.8 15.9 9.68 18 15.4 Zr 201 228 258 242 215 180 231 203 Nb 11.9 13.5 13.8 12.4 11 10.4 12 11.2 Hf 5.09 5.88 6.4 5.79 4.86 4.77 5.82 5.09 Ta 0.966 1.04 1.21 0.907 0.852 0.825 0.944 0.956 Th 10.9 9.18 11.7 10 9.68 10 10.8 11.5 U 1.29 1.16 1.23 0.975 0.844 1.74 1.01 1.21 Pb 12.2 11.9 11.8 12.5 11.3 12.2 12.1 13.1 Ga 15.3 15.7 16.3 16.4 14.7 13.9 14.8 14.2 Cu 4.78 7.8 4.68 2.62 2.55 1.98 2.59 2.07 Zn 37.6 40.9 56.1 32.2 29.1 22.7 30.3 26.8 Mo 2.33 3.46 1.93 0.714 0.907 1.26 0.448 0.817 Cd 0.18 0.203 0.219 0.122 0.094 0.088 0.094 0.082 In 0.047 0.05 0.039 0.024 0.02 0.018 0.023 0.016 Sb 0.554 0.689 0.562 0.038 0.022 0.062 0.033 0.084 Cs 7.34 9.31 6.05 1.54 1.68 1.91 1.77 1.59 W 1.45 1.43 1.04 0.172 0.306 0.221 0.191 0.264 Re 0.004 0.003 0.003 0.006 0.004 0.005 < 0.002 0.004 Tl 0.932 0.982 0.956 0.527 0.436 0.431 0.462 0.428 Bi 0.053 0.093 0.074 0.012 0.032 0.035 0.019 0.03 注:主量元素含量单位为%,微量和稀土元素为10-6 -
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