Geochemical characteristics and formation age of Keke Pluton in South Qilian Mountain, Qinghai Province
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摘要:
为探讨南祁连喀克图蒙克山科克岩体的构造属性,对南祁连喀克图蒙克山中奥陶世科克岩体进行了详细的地球化学和定年研究。研究结果表明,该岩体主体岩性为正长花岗岩,具有高SiO2(68.41%~73.10%)、高Al2O3(13.03%~14.35%)的特征,亏损高场强元素Nb、P、Ti和重稀土元素,发育明显的负Eu异常,反映岩石经历了强烈的分离结晶作用,其稀土元素配分曲线类型与壳源花岗岩相似;构造成因分类图解表明,这些花岗岩属同碰撞环境的产物。LA-ICP-MS锆石U-Pb测年结果表明,岩体形成于461±2.7Ma,时代为中奥陶世,表明该岩体的源岩为壳源或壳幔混合的产物。结合区域地质特征认为,该岩体为同碰撞作用的产物,佐证了南祁连地块在奥陶纪处于挤压状态,对进一步研究南祁连造山带的演化具有重要意义。
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关键词:
- LA-ICP-MS锆石U-Pb测年 /
- 地球化学 /
- 南祁连
Abstract:Lying in the middle of Kaketumengke Mountain, the Keke pluton which was formed in Middle Ordovician is located in the southeastern part of South Qilian massif. Geochemical and geochronological studies were conducted to investigate the tectonic at-tribute of the Keke pluton. The pluton is mainly composed of syenogranite and is characterized by high content of SiO2 (68.41%~73.10%) and high content of Al2O3 (13.03%~14.35%). Geochemical data also show depletion of Nb, P, Ti and HREE with Eu nega-tive anomaly. The REE patterns show the characteristics of crustal anatectic granite, and the genetic classification diagram shows that the granite was formed in a syn-collisional setting. LA-ICP-MS zircon U-Pb dating shows that gneissic granite was formed at 461±2.7Ma. Combined with regional geology, the authors hold that Keke pluton was probably derived from the source of the crust and re-sulted from syn-collision, which supports the argument of compressive regime of the Qilian block during the Mid-Ordovician and is of great significance for the further study of the evolution of the Qilian block.
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Key words:
- LA-ICP-MS zircon U-Pb dating /
- geochemistry /
- South Qilian Mountain
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图 4 科克岩体微量元素原始地幔标准化蛛网图和稀土元素原始地幔标准化分布型式(原始地幔标准化值据参考文献[12])
Figure 4.
表 1 科克侵入岩主量、微量和稀土元素含量及特征值
Table 1. Major, trace, REE compositions features in Keke pluton
样品编号 PM17-YQ1 PM17-YQ2 PM17-YQ3 PM17-YQ4 PM17-YQ5 PM17-YQ6 PM17-YQ7 SiO2 73.10 69.91 70.00 69.74 69.05 68.41 72.50 Al2O3 13.03 13.40 13.54 13.49 14.35 13.67 14.14 Fe2O3 0.73 1.24 1.13 1.07 0.99 0.79 0.44 FeO 1.55 3.25 3.21 3.09 2.44 3.83 1.63 CaO 1.10 1.95 1.85 2.25 2.00 1.95 1.80 MgO 0.37 0.59 0.60 0.69 0.66 1.05 0.48 K2O 5.77 4.14 4.31 4.88 5.63 4.57 5.30 Na2O 2.67 2.84 2.85 2.26 2.51 2.60 2.58 TiO2 0.31 0.62 0.62 0.62 0.63 0.71 0.33 P2O5 0.10 0.14 0.14 0.14 0.14 0.20 0.10 MnO 0.05 0.08 0.08 0.09 0.07 0.09 0.05 烧失量 0.93 1.22 1.08 1.06 1.11 1.52 0.71 H2O+ 0.68 1.20 1.12 1.18 1.06 1.36 0.42 TFe2O3 2.45 4.85 4.70 4.50 3.70 5.05 2.25 总计 0.98 1.01 1.01 1.01 1.01 1.01 1.01 A/CNK 1.03 1.06 1.07 1.03 1.04 1.07 1.07 SI 3.34 4.89 4.96 5.76 5.40 8.18 4.60 AR 2.22 2.17 2.18 1.81 1.89 2.00 1.96 σ 2.36 1.81 1.90 1.91 2.55 2.01 2.11 R1 2513.00 2555.00 2515.00 2572.00 2276.00 2450.00 2588.00 R2 393.00 503.00 495.00 539.00 527.00 536.00 490.00 DI 89.72 81.02 81.55 80.03 82.10 78.84 85.29 Rb 37.1 78.8 73.5 76.2 62.5 73.5 38.8 K 47900 34368 35779 40511 46737 37938 43998 Ba 937 1080 1090 1220 1100 957 560 Th 20.3 26.9 27.1 31.1 42.6 7 24.6 U 1.3 1.85 1.88 2 1.94 1.44 2.83 Nb 11 15.2 16.9 18.4 24.7 21.5 9.14 La 65.94 102.31 151 116.24 124.53 107.03 75.1 Ce 118.36 166.96 227 203.11 187.57 130.09 128 Sr 92.4 161 157 170 104 140 128 Nd 43.58 70.92 111.6 81.09 71.69 69.88 52.81 Zr 166 342 320 337 531 214 132 Hf 5.85 9.76 9.83 9.58 15.1 6.77 5.79 Sm 7.96 12.92 18.27 14.37 13.42 14.53 10.59 Ti 1858 3717 3717 3717 3777 4257 1978 Y 39.78 57.02 60.71 57.24 52.49 72.86 53.28 Yb 4.36 5.78 5.83 5.69 4.53 6.31 4.43 Lu 0.67 0.86 0.86 0.86 0.72 0.94 0.65 La 65.94 102.31 151 116.24 124.53 107.03 75.1 Ce 118.36 166.96 227 203.11 187.57 130.09 128 Pr 11.77 19.04 30.19 21.89 20 18.47 14.71 Nd 43.58 70.92 111.6 81.09 71.69 69.88 52.81 Sm 7.96 12.92 18.27 14.37 13.42 14.53 10.59 Eu 1.08 2.38 2.71 2.48 1.91 3.27 1.71 Gd 7.32 11.51 16.17 12.94 11.88 13.7 9.84 Tb 1.32 2.06 2.67 2.24 2.06 2.63 1.83 Dy 6.75 10.04 11.97 10.69 10.19 12.93 9.06 样品号 PM17-1 PM17-2 PM17-3 PM17-4 PM17-5 PM17-6 PM17-7 Ho 1.25 1.77 1.99 1.82 1.88 2.39 1.7 Er 3.64 5.05 5.69 5.2 4.89 6.56 4.74 Tm 0.68 0.87 0.93 0.91 0.76 1.08 0.76 Yb 4.36 5.78 5.83 5.69 4.53 6.31 4.43 Lu 0.67 0.86 0.86 0.86 0.72 0.94 0.65 Y 39.78 57.02 60.71 57.24 52.49 72.86 53.28 ΣREE 274.66 412.48 586.86 479.53 456.02 389.79 315.93 LREE 248.69 374.54 540.77 439.17 419.12 343.27 282.93 HREE 25.97 37.94 46.09 40.36 36.9 46.53 33 LREE/HREE 9.57 9.87 11.73 10.88 11.36 7.38 8.57 LaN/YbN 14.26 16.68 24.43 19.24 25.88 15.98 15.99 δEu 0.46 0.63 0.51 0.58 0.49 0.75 0.54 δCe 0.74 0.67 0.6 0.71 0.64 0.51 0.69 注:测试单位为国土资源部西安矿产资源监督检测中心;主量元素含量单位为%,微量和稀土元素含量为10-6 表 2 正长花岗岩岩体锆石U-Th-Pb测试结果
Table 2. Zircon U-Th-Pb analytical results of syenogranite
测点编号 元素含量/10-6 Th/
U同位素比值 年龄/Ma 谐和度 Pb Th U 207Pb/206Pb 207Pb/235U 206Pb/238U 207Pb/206Pb 207Pb/235U 206Pb/238U 测值 1σ 测值 1σ 测值 1σ 测值 1σ 测值 1σ 测值 1σ 1 75 429 726 0.59 0.0553 0.0014 0.5328 0.0133 0.0700 0.0007 433 54 434 9 436 4 99% 2 46 208 369 0.57 0.0803 0.0039 0.8620 0.0523 0.0743 0.0010 1206 96 631 29 462 6 69% 3 38 206 358 0.58 0.0586 0.0018 0.5634 0.0176 0.0699 0.0009 554 67 454 11 436 5 95% 4 66 236 717 0.33 0.0585 0.0012 0.5660 0.0123 0.0700 0.0006 550 46 455 8 436 3 95% 5 60 221 592 0.37 0.0569 0.0016 0.5779 0.0153 0.0741 0.0007 487 56 463 10 461 4 99% 6 43 246 334 0.74 0.0554 0.0017 0.5806 0.0194 0.0761 0.0012 428 66 465 12 473 7 98% 7 61 264 594 0.44 0.0564 0.0013 0.5771 0.0139 0.0742 0.0008 478 50 463 9 462 5 99% 8 105 364 1198 0.30 0.0562 0.0011 0.5415 0.0110 0.0699 0.0006 461 44 439 7 436 4 99% 9 55 206 577 0.36 0.0582 0.0015 0.5640 0.0157 0.0700 0.0006 539 57 454 10 436 4 95% 10 47 179 452 0.40 0.0585 0.0015 0.5939 0.0139 0.0745 0.0009 550 56 473 9 463 5 97% 11 68 437 521 0.84 0.0570 0.0016 0.5528 0.0146 0.0706 0.0007 500 63 447 10 440 4 98% 12 49 223 421 0.53 0.0696 0.0019 0.6883 0.0197 0.0716 0.0007 917 57 532 12 446 4 82% 13 90 619 698 0.89 0.0638 0.0014 0.6197 0.0136 0.0706 0.0007 744 51 490 9 440 4 89% 14 46 227 380 0.60 0.0571 0.0017 0.5838 0.0171 0.0741 0.0006 494 69 467 11 461 4 98% 15 91 629 706 0.89 0.0628 0.0013 0.5693 0.0116 0.0656 0.0005 702 44 458 8 409 3 88% 16 139 356 782 0.45 0.0693 0.0012 1.1547 0.0247 0.1200 0.0014 909 36 779 12 731 8 93% 17 52 147 506 0.29 0.0831 0.0028 0.8243 0.0300 0.0710 0.0007 1272 67 610 17 442 4 68% 18 49 228 426 0.53 0.0563 0.0015 0.5760 0.0153 0.0742 0.0008 465 57 462 10 461 5 99% 19 47 301 354 0.85 0.0551 0.0016 0.5648 0.0164 0.0745 0.0008 417 65 455 11 463 5 98% 20 40 192 381 0.50 0.0562 0.0016 0.5458 0.0154 0.0705 0.0007 461 61 442 10 439 4 99% 21 55 275 504 0.55 0.0567 0.0013 0.5499 0.0131 0.0703 0.0006 480 52 445 9 438 4 98% 22 41 187 357 0.52 0.0576 0.0021 0.5880 0.0217 0.0739 0.0006 522 80 470 14 460 4 97% 23 48 234 438 0.53 0.0550 0.0014 0.5317 0.0128 0.0703 0.0006 413 49 433 8 438 4 98% 24 57 286 519 0.55 0.0558 0.0013 0.5348 0.0126 0.0697 0.0006 456 54 435 8 435 4 99% 25 119 533 1087 0.49 0.0738 0.0023 0.6903 0.0232 0.0675 0.0005 1035 62 533 14 421 3 76% 26 50 247 403 0.61 0.0559 0.0013 0.5716 0.0139 0.0742 0.0006 450 54 459 9 461 4 99% 27 65 233 692 0.34 0.0575 0.0012 0.5566 0.0126 0.0702 0.0006 522 51 449 8 437 4 97% 28 65 281 642 0.44 0.0559 0.0011 0.5411 0.0107 0.0704 0.0006 456 17 439 7 438 3 99% 29 55 264 502 0.53 0.0554 0.0013 0.5664 0.0131 0.0744 0.0007 428 52 456 8 462 4 98% 30 53 266 488 0.54 0.0569 0.0014 0.5482 0.0133 0.0700 0.0007 487 52 444 9 436 4 98% -
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