LA-ICP-MS zircon U-Pb dating and geochemical characteris-tics of Baoxing rock mass in Xifeng area of northern Liaoning Province
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摘要:
宝兴岩体位于华北板块北缘陆缘活动带东段,岩性为花岗闪长岩,LA-ICP-MS锆石206Pb/238U年龄加权平均值为235.0±1.3Ma,属于中三叠世。岩石的K2O/Na2O平均值为1.07,属高钾钙碱性系列;富集大离子亲石元素,亏损高场强元素,具有活动陆缘钙碱性岩系特征;稀土元素总量平均值为147×10-6,稀土元素配分曲线右倾,属具中等负Eu异常的轻稀土元素富集、重稀土元素亏损型。通过岩石学、岩石地球化学及年代学研究,结合邻区构造演化研究,认为中三叠世研究区在伸展作用下岩石圈进行拆沉,从而形成大规模的岩浆活动。
Abstract:Located on the northern margin of North China Block, the Baoxing rock mass is mainly composed of granodiorite. According to LA-ICP-MS zircon U-Pb dating, it was formed in Middle Triassic, with the 206Pb/238U age of 235.0±1.3Ma. The average K2O/Na2O ratio is 1.07, indicating that the rocks belong to high-K calc-alkaline series. The rocks are enriched in LILE and depleted in HFSE, showing typical features of calc-alkaline series on an active continental margin. The average total amount of REE is 147×10-6, and the curve exhibits obvious right-inclined feature on REE distribution pattern, suggesting that the rocks are of the type of LREE enrichment and HREE depletion with medium negative Eu anomaly. According to the petrology, geochemistry and geochronology in combination with the tectonic evolution research on adjacent areas, lithospheric delamination occurred under the extension in the study area, and then caused a large-scale magmatic activity in the Middle Triassic.
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图 1 研究区地质简图(大地构造位置图据参考文献①修改)
Figure 1.
表 1 宝兴岩体主量、微量和稀土元素分析结果
Table 1. The analyses of major, trace and rare earth elements of Baoxing rock mass
样品编号 PM023-4-TY1 PM023-11-TY1 PM023-11-TY2 PM023-16-TY1 PM023-20-TY1 平均值 SiO2 68.24 74.06 52.36 57.02 60.98 62.53 TiO2 0.58 0.16 0.82 1.11 0.65 0.66 Al2O3 15.12 14.5 15.97 17.34 15.7 15.73 Fe2O3 2.69 1.27 3.83 3.3 2 2.62 FeO 1.35 0.58 3.86 5.02 3.6 2.88 MnO 0.18 0.05 0.2 0.18 0.12 0.15 MgO 1.64 0.61 3.13 3.66 3.28 2.46 CaO 0.76 0.44 5.45 2.97 4.43 2.81 Na2O 3.48 3.00 0.76 3.96 3.55 2.95 K2O 3.2 3.95 4.27 1.86 2.51 3.16 P2O3 0.18 0.04 0.15 0.24 0.22 0.17 烧失量 2.55 1.32 8.37 3 2 3.45 合计 99.97 99.98 99.17 99.66 99.04 99.57 K 26553 32776 35431 15434 20827 26204 Rb 107 109 179 62.2 62 103.84 Ba 588 500 432 886 868 654.8 Th 10.1 8.05 6.18 8.86 5.23 7.68 Ta 0.73 0.37 0.47 0.73 0.46 0.55 Nb 11 8.52 6.86 17.5 13.9 11.56 Zr 112 100 116 210 257 159 Hf 3.58 3.71 4.33 7.3 6.79 5.14 Sr 234 208 354 431 675 380.4 La 36.9 27 19.9 38.5 33.3 31.12 Ce 66.1 45 40.9 77.1 67.3 59.28 Pr 8.64 5.24 5.03 10.3 8.41 7.52 Nd 31.8 16.1 17.9 39.8 33.8 27.88 Sm 5.97 2.63 3.80 7.61 6.99 5.4 Eu 1.56 0.72 1.17 1.78 1.67 1.38 Gd 5.37 2.39 3.32 6.74 5.98 4.76 Tb 0.77 0.3 0.58 1.03 0.86 0.71 Dy 4.47 1.6 3.46 5.65 4.85 4.01 Ho 0.86 0.29 0.72 1.27 0.92 0.81 Er 2.32 0.82 1.98 3.41 2.64 2.23 Tm 0.35 0.1 0.32 0.56 0.43 0.35 Yb 1.97 0.71 1.97 3.41 2.54 2.12 Lu 0.32 0.1 0.35 0.53 0.47 0.35 Y 22.5 9.68 20.1 32.3 27.1 22.34 ΣREE 167.4 103 101.4 197.69 170.16 147.93 LREE 150.97 96.69 88.70 175.09 151.47 132.58 HREE 22.90 38.84 15.76 16.84 17.63 15.35 LREE/HREE 9.19 15.34 6.98 7.75 8.10 9.47 (La/Yb)N 12.63 25.64 6.81 7.61 8.84 12.31 δEu 0.83 0.86 0.99 0.74 0.77 0.84 (La/Sm)N 3.89 6.46 3.29 3.18 3 3.63 (Gd/Yb)N 2.20 2.72 1.36 1.59 1.90 1.81 Sm/Nd 0.19 0.16 0.21 0.19 0.21 0.19 A/CNK 1.43 1.45 1.01 1.25 0.95 1.22 σ43 1.74 1.55 2.09 2.27 1.97 1.92 注:主量元素含量单位为%,微量和稀土元素单位为10-6 表 2 宝兴岩体花岗闪长岩LA-ICP-MS锆石U-Th-Pb同位素分析结果
Table 2. LA-ICP-MS zircon U-Th-Pb isotope analytical data of Baoxing granodiorite rock
点号 Pb/10-6 232Th/10-6 238U/10-6 Th/U 同位素比值 同位素年龄值/Ma 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 208Pb/232Th 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 208Pb/232Th 1σ 1 20.8 330 450 0.73 0.0508 0.002 0.2599 0.011 0.0370 0.001 0.0115 0.001 232 89 235 9 234 3 230 10 2 26.2 459 554 0.83 0.0533 0.003 0.2726 0.016 0.0372 0.001 0.0112 0.001 339 140 245 13 235 4 224 10 3 35.0 520 779 0.67 0.0513 0.002 0.2613 0.008 0.0372 0.001 0.0109 0.001 254 68 236 7 235 3 218 8 4 30.0 819 544 1.50 0.0519 0.002 0.2653 0.009 0.0372 0.001 0.0104 0.001 283 74 239 7 235 3 208 8 5 19.7 336 431 0.78 0.0525 0.002 0.2694 0.010 0.0371 0.001 0.0100 0.001 306 81 242 8 235 3 201 8 6 21.8 224 491 0.46 0.0517 0.002 0.2670 0.009 0.0376 0.001 0.0105 0.001 272 78 240 7 238 3 212 9 7 48.3 1366 879 1.55 0.0514 0.003 0.2649 0.018 0.0373 0.001 0.0104 0.001 257 182 239 14 236 3 209 8 8 14.5 235 314 0.75 0.0532 0.002 0.2718 0.012 0.0374 0.001 0.0108 0.001 339 102 244 10 237 4 217 9 9 33.0 767 658 1.17 0.0518 0.002 0.2657 0.009 0.0374 0.001 0.0104 0.001 276 74 239 7 236 3 210 8 10 22.9 477 467 1.02 0.0541 0.002 0.2720 0.011 0.0366 0.001 0.0103 0.001 376 103 244 9 232 3 208 9 11 24.7 733 528 1.39 0.0530 0.003 0.2683 0.013 0.0369 0.001 0.0058 0.001 328 109 241 10 233 3 116 5 12 21.8 293 493 0.59 0.0521 0.002 0.2654 0.011 0.0372 0.001 0.0106 0.001 287 87 239 9 236 4 212 10 13 32.2 482 689 0.70 0.0528 0.002 0.2698 0.009 0.0372 0.001 0.0104 0.001 317 74 243 7 235 3 208 9 14 29.8 352 644 0.55 0.0519 0.002 0.2671 0.009 0.0377 0.001 0.0106 0.001 280 78 240 7 238 4 213 10 15 30.5 599 607 0.99 0.0515 0.002 0.2619 0.008 0.0370 0.001 0.0105 0.001 261 69 236 7 234 4 210 9 16 21.4 362 433 0.84 0.0526 0.003 0.2669 0.016 0.0369 0.001 0.0103 0.001 309 137 240 13 234 3 208 11 17 30.6 593 613 0.97 0.0515 0.003 0.2570 0.013 0.0363 0.001 0.0099 0.001 261 94 232 11 230 4 200 8 18 22.7 404 447 0.90 0.0522 0.002 0.2655 0.008 0.0372 0.001 0.0104 0.001 295 74 239 7 236 3 210 8 19 25.6 342 544 0.63 0.0513 0.002 0.2617 0.009 0.0371 0.001 0.0105 0.001 254 69 236 7 235 3 212 8 20 28.2 505 551 0.92 0.0528 0.002 0.2687 0.010 0.0370 0.001 0.0107 0.001 320 116 242 8 234 3 216 8 21 37.5 614 758 0.81 0.0508 0.001 0.2567 0.007 0.0366 0.001 0.0105 0.001 232 66 232 6 232 3 211 8 22 33.1 589 621 0.95 0.0513 0.002 0.2627 0.009 0.0374 0.001 0.0107 0.001 254 80 237 7 236 3 215 8 23 26.9 416 526 0.79 0.0518 0.003 0.2692 0.015 0.0374 0.001 0.0104 0.001 280 120 242 12 237 4 209 9 24 16.1 281 304 0.92 0.0529 0.003 0.2700 0.016 0.0371 0.001 0.0110 0.001 324 135 243 13 235 4 221 11 25 7.5 62 157 0.40 0.0515 0.005 0.2619 0.026 0.0370 0.001 0.0125 0.001 265 225 236 21 234 5 252 18 -
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