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摘要:
通过对澜沧江北段卡贡地区出露的纽多黑云母二长花岗岩的岩石学、岩石地球化学及锆石U-Pb年龄的研究，分析了纽多黑云母二长花岗岩的地球化学和原岩特征。黑云母二长花岗岩中的锆石具有明显的振荡环带，较高的Th/U值（普遍大于0.4），属于典型的岩浆成因锆石，用LA-ICP-MS测得锆石206Pb/238U年龄为243.6±1.4Ma（MSWD=1.00，n=15），时代为中三叠世。岩石地球化学特征表明，该黑云母二长花岗岩具有较高的SiO2、Al2O3及高钾富碱的特征，A/CNK值为1.05~1.08，为过铝质高钾钙碱性系列；稀土元素配分模式显示，配分曲线为右倾型，具有明显的负Eu异常和弱负Ce异常，表现为Nb、Ta、P、Zr、Ti等高场强元素相对亏损，相对富集Rb、K、Th、U等大离子亲石元素。岩石地球化学特征表明，纽多黑云母二长花岗岩为S型花岗岩，形成于地壳加厚增温环境下的深熔作用。
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关键词:
- 黑云母二长花岗岩 /
- 地球化学 /
- LA-ICP-MS锆石U-Pb测年 /
- 西藏纽多
Abstract:This paper presents geochronological and whole-rock geochemical data of Niuduo biotite monzogranite exposed in the north of Lancang granitoids to discuss the origin of the Niuduo biotite monzogranite and its geochemical characteristics. Zircons of biotite monzogranite show no euhedral crystals and have clear oscillatory zones as well as high Th/U ratios, suggesting magmatic origin. Zircon LA-ICP-MS dating of the biotite monzogranite yielded an age of 243.6±1.4Ma(MSWD=1.00, n=15), implying that the crystallization of the biotite monzogranite body took place in Middle Triassic. Petrological and geochemical studies show that it is characterized by high silicon and aluminum as well as abundant alkali, with A/CNK being 1.05~1.08, thus belonging to high-K calc-alkaline series. The whole-rock geochemical characteristics such as strongly fractionated REE pattern, apparently negative Eu anomalies and Ce anomalies, depleted Nb, Ta, P, Zr, Ti, and high Rb, K, Th, U suggest that it belongs to S-type granite. The authors hold that the melting took place at about 25km in the middle crust due to extension of the thickened crust after the closure of the paleo-Lancang Ocean. The results obtained by the authors support the hypothesis that the Lancang River tectonic zone represents a remnant Paleo-Tethyan main ocean preserved in the collision suture along a Gondwana-derived microcontinent.
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Key words:
- biotite monzogranite /
- geochemistry /
- LA-ICP-MS zircon U-Pb dating /
- Niuduo, Tibet
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表 1 纽多黑云母二长花岗岩全岩主量、微量和稀土元素分析结果
Table 1. Whole-rock major, trace and rare earth element data of the Niuduo biotite monzogranite
样品号 D6057H1 D6058H1 D6059H1 D6116H1 SiO2 69.70 71.08 72.84 72.52 Al2O3 14.46 14.53 14.08 14.36 TFe2O3 3.29 1.82 2.86 2.57 CaO 1.06 1.33 1.68 1.70 Na2O 4.09 4.96 3.65 4.50 K2O 4.76 2.77 3.65 2.94 MnO 0.067 0.028 0.046 0.049 MgO 0.33 0.81 0.19 0.21 P2O5 0.065 0.056 0.063 0.039 TiO2 0.36 0.25 0.32 0.32 H2O+ 1.58 1.88 0.92 1.20 烧失量 2.69 2.01 1.03 1.36 总量 100.86 99.64 100.41 100.58 Na2O+K2O 8.85 7.73 7.30 8.44 A/NK 1.22 1.30 1.41 1.36 A/CNK 1.05 1.07 1.08 1.05 Li 16.4 7.08 19.5 17.1 Be 4.70 1.91 4.23 7.10 Sc 6.51 5.77 7.45 5.58 V 13.1 6.95 8.09 11.7 Cr 5.89 8.40 5.99 6.22 Co 1.76 3.65 3.31 2.34 Ni 2.27 38.5 4.74 2.86 Cu 5.50 6.99 21.9 6.22 Zn 90.0 94.2 262 107 Ga 25.3 24.2 26.0 29.6 Rb 179 96.3 172 73.3 Sr 113 133 109 120 Zr 16.9 27.4 20.0 18.8 Nb 48.1 50.0 46.2 36.5 Mo 1.08 1.53 1.10 0.87 Ba 528 158 417 142 Hf 0.81 0.56 0.58 0.36 Ta 3.34 2.55 3.11 2.12 Pb 79.1 57.7 184 41.9 Bi 0.36 0.11 0.13 0.05 Th 41.0 23.1 32.4 20.5 U 7.95 2.68 4.80 3.17 Y 79.5 30.8 53.0 34.4 La 103 45.0 58.4 47.2 Ce 200 92.8 123 82.5 Pr 18.1 14.2 21.6 17.7 Nd 68.9 53.9 79.4 66.9 Sm 12.3 8.28 11.9 8.77 Eu 1.51 0.86 1.49 1.14 Gd 11.1 6.89 9.87 7.04 Tb 1.97 0.95 1.41 0.96 Dy 13.8 5.73 9.12 5.69 Ho 2.80 1.01 1.67 1.07 Er 7.99 2.70 4.97 3.04 Tm 1.29 0.39 0.75 0.35 Yb 8.90 2.56 7.69 3.13 Lu 1.25 0.35 0.75 0.56 ΣREE 452.79 235.61 332.49 246.08 LREE 403.70 215.04 296.26 224.24 HREE 49.09 20.57 36.24 21.84 LREE/HREE 8.22 10.45 8.18 10.27 (La/Yb)N 8.29 12.63 5.45 10.81 δEu 0.39 0.34 0.41 0.43 δCe 1.05 0.89 0.85 0.70 注：主量元素含量单位为%，微量和稀土元素为10-6 
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表 2 纽多黑云母二长花岗岩(D6116样品) LA-ICP-MS锆石U-Th-Pb分析结果
Table 2. LA-ICP-MS zircon U-Th-Pb analytical data of the Niuduo biotite monzogranite
测点号 Pb Th U Th/U 同位素比值 年龄/Ma /10-6 207Pb/
206Pb1σ 207Pb/
235U1σ 206Pb/
238U1σ 207Pb/
206Pb1σ 207Pb/
235U1σ 206Pb/
238U1σ 01 30.5 258 695 0.37 0.0495 0.0014 0.2644 0.0074 0.0386 0.0004 172 64.8 238 5.9 244 2.4 04 38.6 457 857 0.53 0.0503 0.0013 0.2648 0.0068 0.0380 0.0004 206 59.3 239 5.5 240 2.2 05 10.7 153 222 0.69 0.0503 0.0022 0.2655 0.0115 0.0385 0.0005 209 104 239 9.3 243 3.3 06 46.4 526 1016 0.52 0.0557 0.0018 0.2956 0.0112 0.0380 0.0004 443 76.8 263 8.8 240 2.5 07 18.0 188 403 0.47 0.0569 0.0022 0.2998 0.0121 0.0381 0.0005 487 87.0 266 9.5 241 3.0 08 21.1 241 474 0.51 0.0514 0.0016 0.2714 0.0090 0.0382 0.0004 257 69.4 244 7.2 241 2.7 09 8.7 111 182 0.61 0.0555 0.0030 0.2974 0.0150 0.0390 0.0006 432 119 264 11.8 247 3.7 10 29.5 271 685 0.40 0.0504 0.0016 0.2653 0.0083 0.0381 0.0004 217 74.1 239 6.7 241 2.4 12 17.7 150 408 0.37 0.0494 0.0023 0.2645 0.0124 0.0388 0.0005 169 111 238 10.0 245 2.9 13 16.2 182 359 0.51 0.0467 0.0022 0.2513 0.0115 0.0391 0.0005 35.3 107 228 9.3 247 3.4 14 8.6 93.6 193 0.49 0.0505 0.0025 0.2691 0.0132 0.0389 0.0005 220 117 242 10.6 246 3.3 15 29.4 414 626 0.66 0.0528 0.0018 0.2841 0.0096 0.0391 0.0005 320 75.9 254 7.6 247 2.9 16 34.9 313 801 0.39 0.0550 0.0019 0.2915 0.0098 0.0384 0.0004 413 71.3 260 7.7 243 2.7 17 11.9 163 257 0.63 0.0549 0.0033 0.2933 0.0162 0.0392 0.0006 409 103 261 12.7 248 3.8 18 20.2 238 444 0.54 0.0549 0.0020 0.2957 0.0104 0.0392 0.0005 409 81.5 263 8.1 248 3.0 02 57.3 472 943 0.50 0.1193 0.0048 0.7123 0.0296 0.0427 0.0004 1946 71.3 546 17.6 270 2.7 03 17.5 210 359 0.59 0.0725 0.0028 0.3948 0.0162 0.0389 0.0005 1011 79.6 338 11.8 246 3.1 11 91.6 632 1838 0.34 0.1204 0.0068 0.7710 0.0661 0.0405 0.0011 1962 102 580 37.9 256 6.9
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表 3 纽多黑云母二长花岗岩(D6116样品)锆石微量元素LA-ICP-MS分析结果
Table 3. Zircon trace element data obtained by LA-ICP-MS for migmatite from the Niuduo biotite monzogranite
测点号 01 04 05 06 07 08 09 10 12 13 14 15 16 17 18 02 03 11 P 888 479 267 1061 5015 561 339 462 307 446 358 538 496 386 411 507 491 639 Ti 3.00 4.23 10.90 3.98 6.40 6.39 9.49 3.98 4.72 6.37 8.74 8.64 3.90 8.90 3.86 3.67 9.49 6.71 Y 1297 2198 2026 2871 1405 1355 1526 1258 927 1094 927 3521 1427 1831 1646 2332 1062 1696 Nb 16.60 12.60 2.79 9.74 11.30 11.10 2.52 17.40 10.50 8.97 4.60 8.73 19.80 3.73 9.47 16.90 8.70 24.00 La 4.11 1.05 0.03 18.20 65.00 0.03 0.01 0.16 0.00 0.00 0.00 0.11 0.01 0.07 0.02 2.63 0.07 19.01 Ce 19.20 16.80 5.31 60.10 208.00 9.73 4.52 10.40 7.90 8.64 5.11 10.40 11.20 6.25 9.08 23.23 7.47 51.35 Pr 1.68 0.62 0.52 6.88 30.70 0.10 0.14 0.09 0.05 0.06 0.08 0.58 0.07 0.35 0.18 1.06 0.11 6.97 Nd 9.19 4.60 7.29 34.2 168 2.00 3.79 1.70 0.79 1.30 1.55 8.57 1.13 4.26 3.09 6.52 2.13 32.95 Sm 5.16 7.95 11.41 17.01 50.52 4.68 7.19 3.13 2.54 3.53 2.84 14.70 3.20 8.19 6.41 8.24 3.25 13.84 Eu 0.026 0.22 0.74 0.20 0.32 0.08 0.36 0.11 0.08 0.08 0.17 0.39 0.12 0.36 0.18 0.55 0.14 4.81 Gd 25.3 43.0 52.2 65.4 74.9 26.9 39.0 20.8 16.4 22.3 21.4 81.5 22.9 43.5 35.2 45.5 21.1 36.1 Tb 9.11 15.74 17.91 22.01 16.72 9.84 12.81 8.71 5.84 7.82 6.54 28.10 9.57 15.60 12.70 17.46 7.48 11.70 Dy 111 194 195 266 154 119 151 108 78.3 94.8 85.9 328 122 174 148 210.0 93.75 130.6 Ho 45.8 76.1 71.2 102.0 49.8 47.2 54.8 43.9 31.8 38.2 32.2 124 48.6 64.5 57.7 81.9 36.5 52.7 Er 209 341 298 443 202 212 230 198 150 171 143 522 225 270 249 364 166 276 Tm 42.6 68.2 58.6 88.2 39.5 43.2 45.3 42.3 31.5 35.6 29.4 101 48.9 53.6 50.9 73.4 34.6 70.3 Yb 394 592 504 765 337 393 401 382 294 327 263 859 429 477 445 641 307 761 Lu 78.7 112 97.9 142 65.3 76.6 76.0 75.5 59.2 63.0 52.0 166.0 83.7 90.9 87.5 120.0 61.4 177.9 Hf 10773 9765 7929 11069 10335 9820 8933 10922 11422 10322 8817 8682 11410 9459 9773 10342 8327 10721 Ta 7.15 5.26 1.24 4.91 4.57 4.54 1.16 7.24 5.14 3.41 1.87 3.58 8.03 1.63 3.82 7.16 3.54 16.69 ΣREE 955 1473 1319 2029 1461 944 1025 895 678 773 643 2243 1004 1209 1105 1595 741 1645 LREE 39.40 31.21 25.32 136.68 521.88 16.63 16.01 15.55 11.36 13.61 9.75 34.67 15.71 19.49 18.95 42.23 13.17 128.93 HREE 915.53 1442.08 1294.11 1892.33 938.80 927.26 1008.93 879.09 666.30 759.12 633.58 2208.95 988.72 1189.19 1086.08 1552.71 728.29 1516.45 LREE/HREE 0.04 0.02 0.02 0.07 0.56 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.03 0.02 0.09 δEu 0.01 0.03 0.08 0.02 0.02 0.02 0.05 0.03 0.03 0.02 0.05 0.03 0.03 0.05 0.03 0.07 0.04 0.62 δCe 1.80 5.00 3.09 1.32 1.13 27.40 9.48 20.30 53.51 46.37 19.62 5.18 49.83 5.10 15.39 3.42 16.80 1.09 注：微量元素含量单位为10-6
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