Volcanic rock geochemical characteristics and zircon U-Pb age of the Kulapuhe Formation-complex in the west of East Kunlun Mountains, Xinjiang
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摘要:
对东昆仑西段库拉甫河岩组火山岩地球化学进行研究,结果显示,主量元素MgO、FeO含量较高,TiO2和K2O含量分别为1.12%、0.63%,与岛弧拉斑玄武岩(0.84%、0.43%)接近;微量元素具有Sr富集,高场强元素Nb、Ta略亏损,P无明显分馏或未分馏的特征,稀土元素球粒陨石标准化配分曲线显示良好的同源性(配分曲线变化规律近似一致),且与富集型洋脊玄武岩配分趋势一致。结合构造环境判别,认为其形成于岛弧环境,具有岛弧拉斑玄武岩的特征,来源于与岛弧相关的富集地幔。利用锆石U-Pb测年获得2组年龄,其中一组年龄为688.7±5.1Ma,代表捕获晶年龄,另一组年龄483.4±3.3Ma为结晶年龄,代表玄武岩的形成年龄,属于早奥陶世。结合其构造环境、岩石地球化学特征和年龄数据,认为其是原特提斯洋俯冲消减环境下的产物,且原特提斯洋俯冲至少持续到早奥陶世。
Abstract:In this paper, the authors conducted the study of volcanic rock geochemistry of the Kulapuheyan Formation-complex in the western part of East Kunlun Mountains. The results show that the values of MgO and FeO are1.12% and 0.63%, respectively, the values of TiO2 and K2O are close to the value of island-arc tholeiite (0.84%, 0.43%, respectively), the distribution of trace elements shows enrichment of Sr, slight depletion of HFSE Nb and Ta, and no significant fractionation or no fractionation of P, with rare earth pellet meteorite distribution curve showing good homologous nature (similar distribution curve variations). And it is consistent with the distribution trend of E-MORB. It is concluded that it was in an island arc environment and had the characteristics of islandarc tholeiite. It was derived from island-related enrichment mantle. The 688.7±5.1Ma represents the age of the captured crystal, and 483.4±3.3Ma is the age of the representative age of the basalts, and belongs to the Early Ordovician. In combination with its tectonic setting, geochemical characteristics and chronology, the authors hold that it was produced by the subtraction of the original Tethys Ocean subduction, and the original Tethys ocean subducted continuously at least until the Early Ordovician.
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Keywords:
- basalt /
- zircon U-Pb dating /
- tectonic evolution /
- East Kunlun
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图 1 东昆仑构造简图(a)[24]、区域地质图(b)①和A-B剖面(c)
Ⅰ-1-1—塔里木南缘中新生代盆地;Ⅱ-2-1—北昆仑早古生代岩浆弧;Ⅱ-2-2—库地-其曼于特混杂岩带;Ⅱ-2-3—中昆仑微地块;Ⅱ-2-4—南昆仑古生代增生杂岩楔;Ⅲ—昆南-羌北缝合带
Figure 1. East Kunlun tectonic map(a), regional geological map of the study area(b)and geological section A-B (c)
图 7 岩石稀土元素球粒陨石标准化配分模式图(a)和微量元素原始地幔标准化蛛网图(b)[36]
OIB—洋岛玄武岩;N-MORB—亏损型洋脊玄武岩;E-MORB—富集型洋脊玄武岩
Figure 7. Chondrite-normalized REE patterns(a)and primitive mantle-normalized spidergrams of trace elements(b)
表 1 样品1411AY-D2-TW1锆石U-Th-Pb年龄分析结果
Table 1 Zircon U-Th-Pb dating results of sample 1411AY-D2-TW1
测点 含量/10-6 Th/U 同位素比值 表面年龄/Ma Th U Pb 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 1 890 534 312 1.67 0.0595 0.0024 0.9244 0.0352 0.1128 0.0013 584 63 665 19 689 7 2 81 332 114 0.24 0.0559 0.0022 0.5992 0.0229 0.0777 0.0008 449 67 477 15 483 5 3 289 230 130 1.25 0.0610 0.0052 0.9482 0.0798 0.1127 0.0019 640 154 677 42 689 11 4 114 178 103 0.64 0.1378 0.0039 2.0777 0.0545 0.1094 0.0013 2200 30 1141 18 669 7 5 107 126 60 0.85 0.0721 0.0079 0.9804 0.1044 0.0986 0.0031 989 167 694 54 606 18 6 261 450 160 0.58 0.0567 0.0033 0.6066 0.0343 0.0776 0.0012 481 98 481 22 482 7 7 135 181 147 0.75 0.0743 0.0026 1.7632 0.0594 0.1722 0.0019 1049 51 1032 22 1024 10 8 240 251 50 0.96 0.0538 0.0132 0.3059 0.0743 0.0413 0.0017 361 399 271 58 261 11 9 221 414 146 0.53 0.0547 0.0015 0.5871 0.0145 0.0779 0.0006 399 41 469 9 484 4 10 56 375 183 0.15 0.0625 0.0014 0.9686 0.0204 0.1125 0.0009 691 32 688 11 687 5 11 68 180 386 0.38 0.1512 0.0025 9.2475 0.1375 0.4437 0.0041 2359 13 2363 14 2367 18 12 117 484 165 0.24 0.0558 0.0015 0.5974 0.0145 0.0777 0.0006 444 40 476 9 482 4 13 221 131 77 1.7 0.0588 0.0031 0.9123 0.0462 0.1126 0.0013 558 90 658 25 688 8 14 95 405 138 0.23 0.0548 0.0016 0.5887 0.0164 0.0780 0.0006 403 48 470 10 484 4 15 139 238 124 0.58 0.0634 0.0029 0.9904 0.0443 0.1133 0.0015 723 73 699 23 692 9 16 434 483 90 0.9 0.0494 0.0022 0.2655 0.0114 0.0390 0.0004 164 82 239 9 247 2 17 92 170 82 0.54 0.0659 0.0035 0.9518 0.0490 0.1047 0.0016 804 83 679 25 642 9 18 281 765 265 0.37 0.0569 0.0012 0.6120 0.0118 0.0780 0.0006 489 30 485 7 484 3 19 256 337 180 0.76 0.0657 0.0017 1.0208 0.0239 0.1126 0.0009 798 35 714 12 688 5 20 126 251 118 0.5 0.0651 0.0038 0.9186 0.0520 0.1023 0.0016 779 92 662 28 628 10 21 883 1767 559 0.5 0.0602 0.0012 0.5757 0.0096 0.0694 0.0005 611 25 462 6 432 3 22 56 133 108 0.42 0.0744 0.0025 1.8333 0.0582 0.1787 0.0020 1053 46 1057 21 1060 11 23 77 205 103 0.38 0.0598 0.0029 0.9350 0.0440 0.1135 0.0015 595 79 670 23 693 9 24 70 168 103 0.42 0.0666 0.0018 1.2486 0.0311 0.1360 0.0012 825 38 823 14 822 7 表 2 样品主量、微量和稀土元素分析结果
Table 2 Major, trace elements and REE analyses of samples
编号 1311AY-P12-1 1311AY-P12-2 1311AY-P12-4 1311AY-P12-4 1311AY-P12-5 岩石名称 灰绿色块状玄武岩 灰绿色块状玄武岩 紫红色杏仁状玄武岩 玄武岩 玄武岩 SiO2 47.86 47.52 45.61 49.27 48.11 TiO2 1.49 0.94 1.23 1.10 0.84 Al2O3 16.10 15.18 14.71 16.22 16.73 Fe2O3 3.18 1.64 7.79 4.29 3.96 FeO 9.65 7.62 4.24 6.79 7.38 MnO 0.16 0.15 0.19 0.20 0.20 MgO 5.73 7.04 5.00 3.75 5.24 CaO 6.36 7.13 8.33 9.94 9.34 Na2O 2.94 2.95 3.30 2.99 2.80 K2O 0.13 0.32 1.89 0.07 0.05 P2O5 0.21 0.15 0.19 0.15 0.09 烧失量 5.19 8.74 7.89 5.06 5.05 Rb 14.59 9.00 27.18 6.30 6.80 Sr 531.00 260.00 252.00 151.00 249.00 Ba 102.00 120.00 250.00 65.11 85.39 Nb 5.36 6.62 6.00 5.32 4.86 Ta 0.29 0.20 0.20 0.53 0.34 Zr 68.22 56.00 52.72 33.91 52.05 Hf 1.87 1.48 1.74 1.05 1.64 Th 2.60 0.66 1.30 2.20 1.20 K 1078.72 2655.32 15682.98 580.85 414.89 P 916.90 654.93 829.58 654.93 392.96 Ti 8940.00 5640.00 7380.00 6600.00 5040.00 Cr 36.50 170.00 41.90 35.08 26.42 U 0.84 0.36 0.39 0.34 0.60 Y 19.70 14.60 18.10 15.80 17.90 La 8.20 6.20 8.50 6.30 6.40 Ce 16.40 12.80 15.80 13.10 12.70 Pr 2.30 1.90 2.30 1.60 1.70 Nd 10.80 8.80 10.60 7.40 8.40 Sm 2.80 2.20 2.40 2.00 2.30 Eu 1.10 0.88 0.96 0.80 0.98 Gd 3.10 2.50 2.90 2.10 2.50 Tb 0.57 0.46 0.51 0.43 0.51 Dy 3.60 2.80 3.20 2.90 3.30 Ho 0.78 0.62 0.71 0.61 0.67 Er 2.00 1.60 1.90 1.80 2.00 Tm 0.29 0.24 0.29 0.29 0.32 Yb 2.00 1.60 2.00 2.00 2.00 Lu 0.28 0.20 0.27 0.31 0.35 ∑REE 54.22 42.80 52.34 41.64 44.13 LREE/HREE 3.30 3.27 3.44 2.99 2.79 δEu 1.14 1.14 1.11 1.18 1.24 (La/Yb)N 2.94 2.78 3.05 2.26 2.30 (La/Sm)N 1.89 1.82 2.29 2.03 1.80 (Gd/Yb)N 1.28 1.29 1.20 0.87 1.03 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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