Zircon U-Pb age and geochemistry of the Guangmashan monzonitic porphyry in Ninglang, Yunnan Province
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摘要:
宁蒗光马山二长斑岩位于扬子陆块西缘、金沙江断裂带小金河断裂与宾川-程海断裂夹持部位。通过对宁蒗光马山二长斑岩进行锆石U-Pb定年，获得年龄为33.37±0.26Ma（MSWD=1.7，1σ），表明其形成时代为渐新世早期，与盐源-丽江富碱斑岩带主体侵位时代一致。岩石SiO2含量为61.55%~69.13%，全碱（Na2O+K2O）含量为8.85%~10.92%，N/K值为0.88~1.07，A/NK值为1.54~1.84，A/CNK值为1.23~1.72，属过铝质碱性石英二长斑岩。同时富集轻稀土元素、亏损重稀土元素，高La/Yb值，低Y、Yb和镁值（Mg# < 0.5），表明其具有大陆型或钾质C型埃达克岩的特征。该岩石可能形成于区内加厚地壳变泥质岩部分熔融，其起源演化受金沙江-红河走滑断裂系控制，是新生代印度-欧亚板块碰撞后伸展构造背景的产物。
Abstract:The Guangmashan monzonitic porphyry in Ninglang is located between Xiaojinhe and Binchuan-Chenhai faults in western Yangtze block. In this paper, the authors carried out LA-ICP-MS zircon U-Pb dating for the monzonite porphyry and obtained a weighted mean age of 33.37±0.26Ma, suggesting Oligocene, which is consistent with the main formation age of Lijiang-Beiya alkali-rich porphyritic belt. The monzonite porphyry shows peraluminous alkaline affinities, with SiO2 content of 61.55%~69.13%, (Na2O+K2O) content of 8.85%~10.92%, N/K ratio of 0.88~1.07, A/NK ratio of 1.54~1.84, and A/CNK ratio of 1.23~1.72. It is also enriched in LREE but depleted in HREE, with high ratio La/Yb, low Y and Yb content, and low values of Mg#(< 0.5). The porphyry shows continent-type potassium C-type adakite characteristics, and might have been derived by partial melting of the thickened lower crust caused by Jinshajiang-Red River strike-slip fault system, formed in an extensional setting at post-collisional stage, caused by the collision between the India and Eurasian blocks.
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Key words:
- zircon U-Pb age /
- geochemistry /
- monzonitic porphyry /
- Ninglang
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表 1 光马山二长斑岩LA-ICP-MS锆石U-Th-Pb同位素分析结果
Table 1. LA-ICP-MS zircon U-Th-Pb dating data for the Guangmashan monzonitic porphyry
测点号 Th/10-6 U/10-6 Th/U Pb/10-6 普通铝(207法)校对后同位素比值 普通铝(207法)校对后表生年龄/Ma 207Pb/206Pb ±1σ 207Pb/U235 ±1σ 206Pb/238U ±1σ 207Pb/206Pb ±1σ 207Pb/235U ±1σ 206Pb/238U ±1σ PM15b5-01 561 637 0.88 3.88 0.0477 0.0034 0.0325 0.0022 0.0050 0.0001 83.4 172 32.5 2.2 32.3 0.5 PM15b5-02 607 767 0.79 4.57 0.0494 0.0038 0.0330 0.0021 0.0050 0.0001 165 180 33.0 2.0 32.4 0.5 PM15b5-03 353 384 0.92 2.46 0.0504 0.0046 0.0346 0.0027 0.0052 0.0001 217 196 34.5 2.6 33.7 0.6 PM15b5-04 549 687 0.80 4.00 0.0469 0.0029 0.0317 0.0018 0.0050 0.0001 42.7 141 31.7 1.7 32.0 0.5 PM15b5-05 662 756 0.88 4.70 0.0477 0.0037 0.0326 0.0021 0.0051 0.0001 83.4 174 32.6 2.1 33.0 0.5 PM15b5-06 536 694 0.77 4.34 0.0483 0.0032 0.0346 0.0023 0.0053 0.0001 122 143 34.5 2.2 33.9 0.5 PM15b5-07 943 959 0.98 6.15 0.0472 0.0025 0.0333 0.0018 0.0051 0.0001 61.2 122 33.2 1.7 33.0 0.5 PM15b5-08 535 669 0.80 4.20 0.0472 0.0029 0.0340 0.0019 0.0053 0.0001 57.5 141 33.9 1.9 33.9 0.5 PM15b5-09 608 590 1.03 3.93 0.0468 0.0030 0.0330 0.0019 0.0052 0.0001 39.0 148 33.0 1.8 33.5 0.6 PM15b5-10 619 738 0.84 4.68 0.0486 0.0034 0.0338 0.0022 0.0052 0.0001 128 156 33.7 2.1 33.4 0.5 PM15b5-11 268 245 1.10 1.69 0.0494 0.0045 0.0346 0.0029 0.0053 0.0001 169 200 34.5 2.8 33.9 0.7 PM15b5-12 844 916 0.92 5.85 0.0475 0.0026 0.0326 0.0017 0.0050 0.0001 76.0 122 32.6 1.7 32.4 0.5 PM15b5-13 504 695 0.73 4.27 0.0468 0.0026 0.0327 0.0018 0.0051 0.0001 39.0 126 32.7 1.8 33.0 0.5 PM15b5-14 470 444 1.06 3.09 0.0489 0.0039 0.0344 0.0023 0.0054 0.0001 143 178 34.3 2.3 34.6 0.6 PM15b5-15 655 794 0.82 4.97 0.0474 0.0027 0.0340 0.0020 0.0052 0.0001 77.9 120 33.9 2.0 33.6 0.5 PM15b5-16 598 540 1.11 3.78 0.0483 0.0031 0.0350 0.0021 0.0053 0.0001 122 131 34.9 2.1 34.0 0.6 PM15b5-17 527 590 0.89 3.87 0.0483 0.0034 0.0344 0.0023 0.0053 0.0001 122 150 34.3 2.2 33.8 0.5 PM15b5-18 903 832 1.09 5.55 0.0478 0.0025 0.0334 0.0017 0.0051 0.0001 87.1 122 33.3 1.7 32.9 0.4 PM15b5-19 606 684 0.89 4.42 0.0473 0.0033 0.0335 0.0022 0.0051 0.0001 64.9 156 33.5 2.2 33.1 0.5 PM15b5-20 456 675 0.67 4.19 0.0479 0.0033 0.0337 0.0021 0.0052 0.0001 98.2 156 33.6 2.1 33.2 0.4 PM15b5-21 403 397 1.02 2.72 0.0491 0.0046 0.0349 0.0029 0.0054 0.0001 154 207 34.8 2.8 34.5 0.7 PM15b5-22 527 634 0.83 4.30 0.0480 0.0030 0.0357 0.0021 0.0054 0.0001 98.2 141 35.6 2.0 34.9 0.5 PM15b5-23 619 459 1.35 3.26 0.0480 0.0040 0.0345 0.0027 0.0053 0.0001 98.2 185 34.4 2.7 34.1 0.6 PM15b5-24 840 811 1.03 5.52 0.0482 0.0030 0.0342 0.0020 0.0052 0.0001 109 141 34.1 2.0 33.6 0.6 PM15b5-25 304 302 1.01 2.03 0.0473 0.0046 0.0329 0.0030 0.0051 0.0001 77.9 202 32.9 3.0 32.8 0.6 PM15b5-26 516 693 0.74 4.43 0.0470 0.0032 0.0331 0.0021 0.0052 0.0001 50.1 161 33.0 2.1 33.1 0.5 PM15b5-27 424 366 1.16 2.60 0.0500 0.0047 0.0349 0.0028 0.0053 0.0001 198 268 34.8 2.8 34.0 0.7 PM15b5-28 533 632 0.84 4.19 0.0474 0.0032 0.0340 0.0022 0.0053 0.0001 77.9 156 34.0 2.1 33.8 0.6 PM15b5-29 355 492 0.72 3.09 0.0481 0.0036 0.0344 0.0024 0.0052 0.0001 106 170 34.3 2.4 33.7 0.7 PM15b5-30 357 469 0.76 2.98 0.0475 0.0036 0.0331 0.0023 0.0052 0.0001 72.3 183 33.1 2.3 33.4 0.6 
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表 2 光马山二长斑岩主量、微量和稀土元素分析结果
Table 2. Analytical results of major, trace elements and REE of the Guangmashan monzonitic porphyry
样品编号 GMS1b1 PM15b1 PM15b2 PM15b3 PM15b4 PM15b5 SiO2 61.55 65.42 66.63 69.13 65.96 67.29 TiO2 0.47 0.38 0.38 0.24 0.36 0.21 Al2O3 16.94 16.10 16.28 15.86 15.89 16.96 Fe2O3 1.59 1.97 1.62 1.61 0.95 1.30 FeO 1.75 1.21 1.48 0.59 2.36 1.04 MnO 0.06 0.03 0.04 0.04 0.07 0.02 MgO 1.85 1.53 1.40 0.22 1.62 0.27 CaO 3.55 1.44 0.62 0.65 1.40 0.61 Na2O 4.78 5.14 4.37 5.27 4.73 5.38 K2O 5.42 4.80 4.48 5.03 4.49 5.54 P2O5 0.37 0.27 0.27 0.10 0.24 0.08 烧失量 1.09 1.33 2.09 0.86 1.65 1.02 总量 99.42 99.62 99.66 99.61 99.71 99.72 Na2O+K2O 10.20 9.94 8.85 10.30 9.22 10.92 Na2O/K2O 0.88 1.07 0.98 1.05 1.05 0.97 A/NK 1.66 1.62 1.84 1.54 1.72 1.55 A/CNK 1.23 1.41 1.72 1.45 1.50 1.47 Sc 6.66 5.33 3.65 1.62 2.89 1.38 Ni 22.80 23.10 22.20 22.10 21.90 22.60 Th 39.80 40.30 38.90 38.50 40.60 39.60 U 8.31 8.92 7.68 6.86 8.73 852.00 La 282.00 119.00 221.00 173.00 169.00 96.70 Ce 486.00 270.00 290.00 265.00 346.00 262.00 Pr 32.50 19.40 18.40 23.60 21.80 17.50 Nd 107.00 64.90 56.60 69.30 68.50 54.60 Sm 15.70 9.54 12.51 7.34 8.96 7.80 Eu 3.81 2.50 3.12 1.83 2.01 1.80 Gd 14.00 8.32 11.01 8.06 9.08 7.01 Tb 1.52 0.92 0.85 0.86 0.98 0.79 Dy 7.03 4.21 5.23 3.16 4.45 3.84 Ho 1.11 0.69 1.01 0.89 0.78 0.69 Er 3.00 1.90 2.58 2.01 2.21 2.03 Tm 0.38 0.24 0.33 0.29 0.36 0.31 Yb 2.16 1.53 1.89 1.73 1.68 2.00 Y 34.80 22.50 26.90 21.30 27.60 22.10 Lu 0.31 0.22 0.29 0.28 0.25 0.33 ∑REE 956.43 503.44 624.81 557.32 636.14 457.35 ∑LREE 927.01 485.34 601.63 540.07 616.27 440.40 ∑HREE 29.42 18.10 23.18 17.25 19.87 16.95 ∑LREE/SHREE 31.51 26.81 25.95 31.31 31.02 25.98 LaN/YbN 93.65 55.79 83.87 71.73 72.16 34.68 δEu 0.79 0.86 0.81 0.73 0.68 0.74 δCe 1.24 1.38 1.12 1.02 1.40 1.56 注：主量元素含量单位为%, 微量和稀土元素含量单位为10-6
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表 3 盐源—丽江地区富碱斑岩年龄统计
Table 3. Age information of the alkali-rich porphyry in Yanyuan-Lijiang area
岩体 岩性 分析方法 年龄值/Ma 数据来源 西范坪 石英二长斑岩 LA—ICPMS锆石U—Pb 31.68±0.28 [12] 光马山 石英二长斑岩 LA—ICPMS锆石U—Pb 33.37±0.26 本文 分水岭 花岗闪长斑岩 LA—ICPMS锆石U—Pb 34.5±0.3 [13] 石支 花岗斑岩 LA—ICPMS锆石U—Pb 35.60±0.58 [10] 花岗斑岩 LA—ICPMS锆石U—Pb 35.9±0.5 [22] 老君山 正长岩 SHRIMP锆石U—Pb 34.8±1.6 [11] 正长岩 LA—ICPMS锆石U—Pb 34.56±0.66 [10] 小桥头 石英二长斑岩 LA—ICPMS锆石U—Pb 34.70±0.54 [10] 喇叭山 粗而斑岩 LA—ICPMS锆石U—Pb 34.74±0.70 [10] 桃花 花岗斑岩 SHRIMP锆石U—Pb 36.35±0.35 [23] 北衙 石英正长斑岩 LA—ICPMS锆石U—Pb 34.92±0.66 [8] 石英正长斑岩 LA—ICPMS锆石U—Pb 36.24±0.63 [14] 石英正长斑岩 LA—ICPMS锆石U—Pb 36.48±0.26 [15]
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