Zircon U-Pb age and geochemical characteristics of Langding intrusion of Shangri-La, Yunnan Province
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摘要:
香格里拉地区广泛分布印支期中-中酸性浅成-超浅成岩体,位于西斑岩带的浪丁岩体主要由角闪闪长玢岩、石英闪长玢岩、含辉石角闪闪长玢岩组成。锆石U-Pb年龄显示岩体侵位于206.4±3.9 Ma。其地球化学特征与埃达克岩相似:SiO2含量为56.66%~64.84%,平均60.42%;Eu异常不明显(Eu/Eu*为0.90~1.23,平均为1.08);富集轻稀土元素和大离子亲石元素,亏损重稀土元素,贫高场强元素;高Sr(490~1165×10-6,平均842×10-6)、Sr/Y(37.4~77.2,平均56.9)、La/Yb(21.7~28.4,平均25.6),低Y(13.1×10-6~17.4×10-6,平均14.6×10-6)、Yb(1.20×10-6~1.56×10-6,平均1.37×10-6)。年代学和地球化学研究结果显示,浪丁岩体形成于岛弧环境下,其形成与晚三叠世甘孜理塘洋壳板片的部分熔融有关,该地区的甘孜-理塘洋壳向西俯冲时,可能以较低的角度进入中咱地块之下。
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关键词:
- LA-ICP-MS锆石U-Pb /
- 构造背景 /
- 角闪闪长玢岩 /
- 义敦岛弧 /
- 香格里拉
Abstract:The west porphyry belt and east porphyry belt in Shangri-La are mainly composed of Indosinian intermediate-acidic intrusive complex rocks.In the western porphyry belt, there are Luanitang porphyry, Xuejiping porphyry, Chundu porphyry, Are porphyry and Langding porphyry from north to south.In the eastern porphyry belt, there are Disuga porphyry, Songnuo porphyry, Pulang porphyry and Lanzhong porphyry from north to south.The Langding porphyry is mainly composed of hornblende diorite porphyrite, quartz diorite porphyrite and pyroxene diorite porphyrite.The zircon U-Pb age indicates that the intrusive rock has an age of 206.4±3.9 Ma.Geochemical characteristics of the Langding porphyry are similar to those of adakite, whose SiO2 is higher than 56.66, averaging 60.42%, and whose δEu is not distinct (0.90~1.23, averaging 1.08).Chondrite-normalized REE patterns show right-inclined feature, and are characterized by enrichment of LREE and LILE, heavy depletion of HREE, high Sr (490×10-6~1165×10-6, averaging 842×10-6), Sr/Y (37.4~77.2, averaging 56.9) and La/Yb (21.7~28.4, averaging 25.6), but low Y (13.1×10-6~17.4×10-6, averaging 14.6×10-6) and Yb (1.20×10-6~1.61×10-6, averaging 1.37×10-6).The results of the studies of major oxides, REEs, trace elements and zircon U-Pb age show that the Langding rock body was formed in an island arc environment, and its formation was related to the partial melting of the low-angle subduction of Garze-Litang oceanic crust slab.
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图 1 香格里拉地区印支期中酸性岩体分布略图(a, 据参考文献[13]修改)和浪丁岩体地质简图(b)
Figure 1.
图 5 浪丁岩体稀土元素配分型式(a)和微量元素蛛网图(b)(球粒陨石标准值和原始地幔标准值据参考文献[22])
Figure 5.
图 6 浪丁岩体构造判别图解[23]
Figure 6.
表 1 浪丁岩体角闪闪长玢岩(AD0526t1)锆石U-Th-Pb同位素数据
Table 1. The zircon U-Th-Pb analytical data of hornblende diorite porphyrite(AD0526t1)of Langding intrusive rock
测点点号 Pb/10-6 U/10-6 U-Pb比值 年龄/Ma 206Pb/238U 1σ 207Pb/235U 1σ 207Pb/206Pb 1σ 206Pb/238U 1σ 207Pb/235U 1σ 207Pb/206Pb 1σ 1 27 627 0.0357 0.0003 0.2538 0.0022 0.0515 0.0004 226 2 230 2 263 17 2 17 390 0.0361 0.0006 0.2626 0.0042 0.0526 0.0007 229 4 237 4 311 28 3 36 763 0.0365 0.0004 0.2622 0.0023 0.0522 0.0004 231 2 236 2 293 17 4 10 243 0.0365 0.0003 0.2557 0.0053 0.0508 0.0010 231 2 231 5 233 47 5 17 439 0.0330 0.0003 0.2273 0.0047 0.0500 0.0010 209 2 208 4 195 48 6 17 402 0.0363 0.0003 0.2613 0.0040 0.0522 0.0008 230 2 236 4 292 34 7 20 434 0.0350 0.0003 0.2570 0.0089 0.0533 0.0015 222 2 232 8 342 65 8 30 723 0.0362 0.0003 0.2650 0.0023 0.0531 0.0005 230 2 239 2 332 19 9 39 920 0.0359 0.0003 0.2537 0.0019 0.0512 0.0003 227 2 230 2 252 15 10 15 360 0.0364 0.0003 0.2546 0.0037 0.0508 0.0007 230 2 230 3 230 31 11 23 271 0.0730 0.0006 0.5728 0.0088 0.0569 0.0009 454 4 460 7 487 33 12 26 659 0.0366 0.0003 0.2522 0.0024 0.0499 0.0004 232 2 228 2 192 19 13 21 488 0.0360 0.0003 0.2556 0.0049 0.0515 0.0009 228 2 231 4 264 40 14 16 114 0.1272 0.0013 1.1417 0.0131 0.0651 0.0007 772 8 773 9 778 21 15 23 564 0.0317 0.0003 0.2257 0.0048 0.0516 0.0011 201 2 207 4 267 48 16 25 605 0.0362 0.0002 0.2521 0.0023 0.0505 0.0004 229 2 228 2 220 20 17 28 742 0.0328 0.0002 0.2375 0.0022 0.0525 0.0005 208 1 216 2 306 20 18 13 73 0.1686 0.0013 1.7340 0.0349 0.0745 0.0014 1004 8 1021 21 1055 37 19 48 285 0.1313 0.0011 1.2081 0.0086 0.0668 0.0004 795 6 804 6 830 13 20 15 373 0.0361 0.0004 0.2555 0.0049 0.0513 0.0009 229 2 231 4 255 41 21 35 967 0.0357 0.0003 0.2534 0.0024 0.0514 0.0004 226 2 229 2 261 20 22 26 609 0.0357 0.0003 0.2546 0.0105 0.0517 0.0017 226 2 230 9 270 76 23 24 655 0.0327 0.0002 0.2318 0.0026 0.0514 0.0005 208 1 212 2 258 24 24 24 804 0.0323 0.0003 0.2291 0.0023 0.0514 0.0004 205 2 209 2 260 20 25 20 498 0.0361 0.0003 0.2504 0.0054 0.0503 0.0009 229 2 227 5 209 44 26 34 818 0.0365 0.0003 0.2533 0.0023 0.0504 0.0004 231 2 229 2 212 19 27 25 588 0.0360 0.0003 0.2580 0.0040 0.0520 0.0008 228 2 233 4 286 34 28 22 520 0.0367 0.0004 0.2630 0.0031 0.0520 0.0005 232 3 237 3 283 23 29 26 570 0.0359 0.0002 0.2529 0.0043 0.0510 0.0008 228 2 229 4 242 38 表 2 浪丁岩体主量、微量和稀土元素分析结果
Table 2. The content of major, trace and rare earth elements of Langding intrusive rock
样品 AD526 AD527 AD528 AD529 AD531 SiO2 60.9 56.6 64.8 59.2 60.5 TiO2 0.63 0.89 0.51 0.70 0.60 Al2O3 13.9 14.5 14.8 14.9 14.7 Fe2O3 0.65 1.11 0.73 2.18 1.34 FeO 3.83 6.15 3.16 4.13 3.48 MnO 0.09 0.17 0.13 0.14 0.09 MgO 3.51 4.89 2.21 3.77 3.37 CaO 4.71 4.71 2.42 4.11 4.55 Na2O 5.33 3.49 3.49 3.61 5.32 K2O 3.81 3.86 5.18 5.04 3.76 P2O5 0.45 0.79 0.29 0.58 0.54 烧失量 1.50 2.16 1.94 1.76 1.33 氧化物总量 99.3 99.4 99.7 100 99.6 TFeO 4.44 7.19 3.84 6.13 4.72 Mg# 59.5 55.7 50.9 49.5 54.5 Cr 36.9 41.4 23.1 36.3 38.6 Ni 13.8 16.8 12.9 16.6 16.0 Rb 54.4 100 71.2 98.0 57.0 Sr 537 1143 873 1164 490 Y 13.6 17.4 13.5 15.1 13.1 Zr 194 184 216 119 117 Nb 10.1 15.3 16.8 11.7 9.7 Ba 2082 2411 2079 3196 2022 La 35.8 41.4 31.2 34.6 32.5 Ce 68.6 77.8 55.7 65.9 60.1 Pr 7.86 9.29 6.23 8.11 7.29 Nd 30.5 35.6 23.4 31.1 27.8 Sm 6.86 7.87 5.56 6.73 5.74 Eu 2.19 2.54 1.89 1.90 1.50 Gd 4.34 5.26 3.41 4.55 4.12 Tb 0.57 0.68 0.48 0.63 0.57 Dy 2.70 3.41 2.45 3.28 2.87 Ho 0.50 0.62 0.48 0.55 0.49 Er 1.37 1.83 1.43 1.57 1.33 Tm 0.20 0.24 0.21 0.23 0.20 Yb 1.26 1.56 1.44 1.41 1.20 Lu 0.21 0.25 0.22 0.23 0.19 Hf 4.75 4.50 5.30 4.30 4.19 Ta 0.64 0.83 0.96 0.76 0.66 Pb 21.2 71.9 83.4 35.9 20.1 Th 11.9 12.9 16.6 11.6 10.0 Sc 15.7 23.8 9.2 15.3 10.0 Eu/Eu* 1.15 1.14 1.23 0.99 0.90 Sr/Y 39.4 65.6 64.5 77.2 37.4 La/Yb 28.4 26.5 21.6 24.6 26.9 注:Mg#=100×Mg/(Mg+Fe2+),FeO=FeO+0.9×Fe2O3;Eu/Eu*(δEu)=2×EuN/(SmN+GdN),N-球粒陨石标准化值据参考文献[22]。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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