LA-ICP-MS zircon U-Pb age and geochemistry of Mengyang granodiorite intrusion in Lianghe area, western Yunnan Province
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摘要:
勐养花岗闪长岩体位于滇西腾冲地块梁河县南勐养镇一带。用LA-ICP-MS技术测得花岗闪长岩锆石U-Pb年龄为115.2±1.0Ma，该年龄被解释为花岗闪长岩的形成年龄，表明该区花岗闪长岩体的形成时代为早白垩世。岩石地球化学特征表明，花岗闪长岩中SiO2含量为62.39%～67.97%，Na2O+K2O为6.26%～7.80%，K2O为1.98%～4.11%，具有贫钾（K2O/Na2O值为0.45～1.11）、低P2O5（0.09%～0.38%）的特征；MgO为1.78%～1.98%，Mg#为34.90～48.40，属于准铝质-弱过铝质钙碱性系列。微量元素具有相对富集大离子亲石元素（U、Th、Rb、Ba）、亏损高场强元素（Tb、Nb、Zr、Hf）的特点。该花岗闪长岩具有I型花岗岩的特征，同时兼有S型花岗岩之特点，具有明显的岩浆混合作用特征。岩石具有岛弧或活动陆缘岩系的微量元素分布特征。地球化学特征和微量元素构造判别图解揭示，勐养早白垩世花岗闪长岩形成于碰撞后岩浆弧环境。花岗闪长岩为幔源岩浆与高黎贡山群古老地壳部分熔融的岩浆混合的产物。该区早白垩世花岗闪长岩是腾冲地块早白垩世侵入岩与班公湖-怒江-泸水-瑞丽洋盆的闭合、洋壳向南西俯冲及板块间的碰撞造山作用的产物。
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关键词:
- 花岗闪长岩 /
- LA-ICP-MS锆石U-Pb年龄 /
- 岩石成因 /
- 腾冲地块 /
- 滇西
Abstract:Mengyang granodiorite intrusion is located in Mengyang area of Tengchong block, western Yunnan Province. LA-ICPMS zircon dating indicates that the granodiorite was emplaced at 115.2±1.0Ma. The granite mass was formed in the Early Creta-ceous. Geochemical data show that the granodiorites has the following data:SiO2=62.39%~67.97%, Na2O+K2O=6.26%~7.80%, K2O/Na2O=0.45~1.11, rich in Si, Na, poor in P, MgO=1.78%~1.98%. Mg#=34.90~48.40, thus belonging to metaluminous to weakly per-aluminous, calc alkaline series. It has both the characteristics of I-type granite and S-type granite in the granodiorite and also has the characteristic of magma mixing. It has Sm/Nd ratios of 0.12~0.20, is enriched in Th, Rb, Ba, Pb and U, and depleted in Ta, Nb, Zr, Hf and Ce, thus similar to features of calc-alkaline rocks in island arc or active continental margin. According to geochemistry and trace element discrimination diagrams for tectonic interpretation, the Early Cretaceous granodiorites are considered to be of the post-collision type formed in a island arc tectonic setting. The granodiorite was from the mixing of mantle-derived magma and par-tial melting crust. The early Cretaceous intrusive rocks in the Tengchong block were intimately related to the closure of the Bangong Co-Nujiang-Longling-Ruili ocean basin and were formed by the subduction of ocean crust and the collision between the Tengchong block and the Zuogong-Baoshan block.
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Keywords:
- granodiorite /
- LA-ICP-MS zircon U-Pb ages /
- rock genesis /
- Tengchong block /
- western Yunnan
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致谢: 审稿专家对本文进行了详细的评审，提出了许多宝贵意见。锆石LA-ICP-MS分析和阴极发光照片得到中国地质大学（武汉）地质过程与矿产资源国家重点实验室胡初、郑曙教授和宗克清博士的帮助，在此一并致以诚挚谢意。
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图 1 研究区区域地质简图及采样位置
Figure 1. Simplified geological map and sampling position of the study area
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图 6 滇西梁河县勐养花岗闪长岩体稀土元素配分模式图（标准化值据参考文献[23]）
Figure 6. REE patterns for trace elements of Mengyang granodiorite in western Yunnan
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图 7 滇西梁河县勐养岩体微量元素原始地幔标准化蛛网图（标准化值据参考文献[23]）
Figure 7. Normalized diagram for trace elements of Mengyang intrusion in western Yunnan
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图 8 勐养花岗闪长岩的锆石CL图像
Figure 8. CL images and U-Pb ages of zircons from granodiorite in Mengyang intrusion
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图 9 勐养花岗闪长岩的锆石U-Pb谐和图(a)和206Pb/238U年龄图(b)
Figure 9. U-Pb concordia diagram and 206Pb/238U age plot of zircon from the granodiorite in Mengyang intrusion
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表 1 勐养花岗闪长岩体的主量、微量和稀土元素的地球化学分析数据
Table 1 Major, trace, and rare earth elements compositions of the Mengyang granodiorite
样品号 D0032 D2346 Pm12-20 D4124 D4179 PM11-45GS1 PM11-63GS1 样品号 D0032 D2346 Pm12-20 D4124 D4179 PM11-45GS1 PM11-63GS1 SiO2 64.70 62.39 62.60 63.46 64.99 63.74 67.97 Hf 3.68 2.68 3.57 7.57 5.57 5.97 4.88 AI2O3 16.68 16.20 16.64 15.54 15.88 16.70 15.48 Sr 425 228 280 489 572 427 222 Fe203 1.21 2.35 3.42 3.54 2.65 3.40 2.35 Cs 2.76 3.70 4.95 1.16 1.42 4.16 4.42 FeO 2.95 3.46 2.41 1.71 1.28 1.64 1.13 Pb 14.30 21.76 17.15 33.30 26.20 18.20 21.30 CaO 4.05 4.56 4.09 3.60 4.06 3.58 2.47 La 63.9 33.8 57.4 101.0 57.4 132.0 78.6 MgO 1.78 1.98 1.92 1.49 1.58 1.32 0.80 Ce 115.0 66.1 108.0 173.0 102.0 189.0 140.0 K2O 1.98 2.37 2.72 3.59 2.76 2.68 4.11 Pr 12.40 7.77 11.50 19.40 11.20 21.60 14.50 Na2O 4.41 3.89 3.90 3.44 3.56 3.64 3.69 Nd 42.4 29.7 41.9 67.7 39.1 67.2 46.9 Ti02 0.51 0.81 0.93 0.92 0.59 0.76 0.50 Sm 7.75 5.87 7.56 11.10 6.10 8.39 7.56 P205 0.09 0.23 0.24 0.38 0.20 0.24 0.15 Eu 1.450 1.460 1.580 2.087 1.364 1.944 1.354 Mn0 0.21 0.10 0.09 0.08 0.07 0.06 0.06 Gd 6.230 5.490 6.650 7.722 4.551 5.580 5.703 烧失量 0.89 1.16 0.62 2.30 2.20 1.16 0.76 Tb 1.080 0.951 1.010 1.230 0.723 0.713 0.860 总量 99.46 99.53 99.58 100.05 99.82 98.92 99.47 Dy 6.06 5.25 5.35 6.17 3.62 3.02 4.38 A/CNK 1.00 0.94 0.99 0.97 0.98 1.08 1.03 Ho 1.290 1.150 1.140 1.290 0.757 0.599 0.914 Mg# 48.0 42.8 42.4 39.8 48.4 37.9 34.9 Er 3.51 3.23 3.03 3.51 2.00 1.72 2.53 Rb 116.0 122.0 138.0 111.0 87.3 125.0 152.0 Tm 0.460 0.437 0.423 0.457 0.277 0.206 0.348 Ba 436 481 960 1190 964 2380 800 Yb 2.91 2.93 2.56 3.07 1.83 1.40 2.21 Th 14.7 12.1 11.7 23.5 17.0 33.9 29.6 Lu 0.410 0.418 0.352 0.435 0.282 0.230 0.307 U 1.72 1.87 1.57 2.86 2.37 2.05 2.40 Y 35.3 29.7 28.6 35.2 20.0 15.5 25.1 Nb 16.2 11.2 13.4 25.9 11.8 13.6 15.5 ∑REE 300.15 194.26 277.06 433.37 251.29 449.10 331.27 Ta 0.82 0.93 1.07 1.42 0.68 0.50 0.87 SEu 0.21 0.26 0.22 0.23 0.26 0.28 0.21 Zr 147.0 95.1 146.0 338.0 245.0 274.0 219.0 (La/Yb)N 14.20 7.46 14.50 21.30 20.30 61.00 23.00 注：主量元素含量单位为%，微量和稀土元素单位为10-6 
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表 2 腾冲地块勐养花岗闪长岩的LA-ICP-MS锆石U-Th-Pb同位素分析结果
Table 2 LA-ICP MS zircon U-Th-Pb data of Mengyang intrusion from Tengchong block
点号 Pb/10-6 Th/10-6 U/10-6 Th/U 同位素比值 年龄/Ma 207Pb/206Pb ±1σ 207Pb/235U ±1σ 206Pb/238U ±1σ 207Pb/235U ±1σ 206Pb/238U ±1σ 01 8.43 257 442 0.58 0.0511 0.0021 0.1257 0.0053 0.0179 0.0002 120.0 4.7 114.3 1.0 02 6.48 210 290 0.72 0.0818 0.0041 0.1995 0.0099 0.0179 0.0002 185.0 8.0 114.0 1.0 03 10.72 377 519 0.73 0.0487 0.0020 0.1224 0.0050 0.0183 0.0002 117.2 4.5 117.0 1.0 04 15.60 292 871 0.34 0.0491 0.0015 0.1207 0.0037 0.0178 0.0002 115.7 3.3 113.5 1.0 05 20.8 1168 860 1.36 0.0493 0.0017 0.1203 0.0041 0.0177 0.0002 115.3 3.7 112.9 1.0 06 20.5 918 864 1.06 0.0497 0.0015 0.1289 0.0039 0.0188 0.0002 123.1 3.5 120.3 1.4 07 19.1 1130 810 1.40 0.0486 0.0021 0.1175 0.0048 0.0177 0.0002 112.8 4.4 112.9 1.5 08 23.35 831 1145 0.73 0.0500 0.0015 0.1212 0.0034 0.0176 0.0002 116.1 3.1 112.6 1.0 09 25.22 776 1259 0.62 0.0489 0.0013 0.1214 0.0032 0.0180 0.0001 116.3 2.9 115.0 1.4 10 15.42 684 664 1.03 0.0607 0.0030 0.1555 0.0094 0.0182 0.0002 146.8 8.3 116.0 1.4 11 17.40 709 832 0.85 0.0493 0.0018 0.1218 0.0043 0.0181 0.0002 116.7 3.9 115.5 1.0 12 26.37 652 1380 0.47 0.0489 0.0014 0.1263 0.0035 0.0188 0.0002 120.7 3.1 120.0 1.0 13 5.44 154 273 0.56 0.0611 0.0036 0.1570 0.0097 0.0187 0.0002 148.1 8.5 119.4 1.5 14 9.96 315 484 0.65 0.0473 0.0020 0.1196 0.0048 0.0185 0.0002 114.7 4.4 118.3 1.3 15 9.73 315 458 0.69 0.0490 0.0020 0.1257 0.0050 0.0186 0.0002 120.2 4.5 118.7 1.1 16 43.51 835 2362 0.35 0.0477 0.0010 0.1174 0.0024 0.0178 0.0001 112.8 2.2 113.5 0.8 17 6.05 189 304 0.62 0.0496 0.0028 0.1188 0.0063 0.0177 0.0002 114.0 5.7 113.2 1.5 18 7.25 232 351 0.66 0.0473 0.0023 0.1160 0.0053 0.0180 0.0002 111.5 4.8 114.9 1.3 19 20.52 768 971 0.79 0.0482 0.0016 0.1178 0.0037 0.0177 0.0001 113.1 3.3 113.1 0.9 20 17.86 929 773 1.20 0.0460 0.0020 0.1130 0.0049 0.0178 0.0002 108.7 4.5 114.6 1.4 21 13.97 404 722 0.56 0.0490 0.0038 0.1187 0.0094 0.0175 0.0003 113.9 8.5 111.6 1.6 22 19.8 951 850 1.12 0.0471 0.0017 0.1167 0.0041 0.0180 0.0002 112.0 3.7 115.1 1.0 23 9.00 584 358 1.63 0.0583 0.0038 0.1430 0.0091 0.0177 0.0003 135.7 8.1 113.1 1.9 24 24.43 451 1323 0.34 0.0559 0.0024 0.1378 0.0058 0.0178 0.0002 131.0 5.2 113.6 1.4 25 15.40 624 675 0.92 0.0522 0.0021 0.1331 0.0053 0.0187 0.0002 126.9 4.8 119.2 1.4
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