LA-ICP-MS zircon U-Pb ages and geological sig-nificance of granodiorite from Zongwulong tectonic belt in Delingha, Qinghai Province
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摘要:
对德令哈市石底泉地区宗务隆构造带内花岗闪长岩进行了锆石U-Pb测年和岩石地球化学分析。岩石地球化学分析结果显示，其具有岛弧或活动大陆边缘花岗岩的属性，原岩可能为新元古代早期（870.0±4.5Ma左右）硅铝地壳或地壳物质熔融的产物，它们的形成与板块的俯冲作用有关LA-ICP-MS锆石U-Pb测年显示2组年龄，分别为870.0±4.5Ma和443.3±2.3Ma。其中870.0±4.5Ma代表源区继承锆石的年龄，反映了新元古代时期的构造岩浆事件；443.3±2.3Ma代表花岗闪长岩岩浆锆石的结晶年龄，即花岗闪长岩侵位于晚奥陶世。综合分析可以确定，宗务隆构造带内花岗闪长岩与柴达木盆地北缘加里东期的板块汇聚碰撞造山作用有关，证实了宗务隆构造带内岩体形成时代并非全部是海西期一印支期。
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关键词:
- 宗务隆构造带 /
- 花岗闪长岩 /
- LA-ICP-MS锆石U-Pb年龄 /
- 地球化学特征
Abstract:Based on a study of zircon U-Pb dating and rock geochemical analysis of granodiorite from Zongwulong tectonic belt in Shidiquan area of Delingha, the authors revealed that the granodiorite has the characteristics of island arc or active continental margin granite. The original rock may be salic crust or the product of crustal melting formed in Early Neoproterozoic (870.0±4.5Ma). The granodiorite samples yielded ages of 870.0±4.5Ma and 443.3±2.3Ma respectively. The age of 870.0±4.5Ma represents provenance in-herited zircon age, which reflects the tectonic magmatic event during the Neoproterozoic, whereas the other age of 443.3±2.3Ma in-dicates the time of zircon crystallization of the granodiorite, which shows that the emplacement occurred in the Late Ordovician. Comprehensive analyses suggest that the granodiorite in the Zongwulong tectonic belt was related to plate convergent collisional orogeny of the Caledonian period on the northern margin of the Qaidam Basin, confirming that the formation of the rock in the Zongwulong tectonic belt did not wholly occurred in Hercynian-Indosinian period.
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致谢: 中国地质调查局西安地质调查中心余吉远高级工程师、李向民研究员对本文提出了宝贵的修改意见，野外工作中得到项目组同事的大力支持和帮助，在此一并表示感谢。
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图 1 石底泉地区地质简图
①—祁连地块；②—宗务隆山-青海南山晚古生代-早古生代裂陷带；③—欧龙布鲁克地块；④—赛什腾-锡铁山-哇洪山早古生代结合带；⑤—柴达木地块
Figure 1. Geological sketch map of Shidiquan area
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图 2 石底泉地区花岗闪长岩野外（a）和显微（b）照片
Figure 2. The macrophotograph(a) and microphotograph(b) of the granodiorite in Shidiquan avea
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图 3 石底泉地区花岗闪长岩R1-R2岩石分类（a）和SiO2-K2O图解（b）（a据参考文献[16]，b据参考文献[17]）
1—厄塞岩；2—碱性辉长岩；3—橄榄辉长岩；4—辉长苏长岩；5—正长辉长岩；6—二长辉长岩；7—辉长岩；8—正长闪长岩；9—二长岩；10—二长闪长岩；11—闪长岩；12—霞石正长岩, 13—正长岩；14—石英正长岩；15—石英二长岩；16—英云闪长岩；17—碱性花岗岩；18—正长花岗岩；19—二长花岗岩；20—花岗闪长岩
Figure 3. R1-R2 rock classification (a) and SiO2-K2O (b) diagrams of the granodiorite in Shidiquan area
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图 4 稀土元素球粒陨石标准化图解（a）及微量元素地幔标准化图解（b）
Figure 4. Chondrite-normalized REE patterns and primitive mantle-normalized multi-element diagram
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图 5 石底泉地区花岗闪长岩锆石阴极发光图像
Figure 5. Cathodoluminescence image of zircons from the granodiorite in Shidiquan area
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图 6 花岗闪长岩锆石U-Pb谐和曲线和206Pb/238U年龄加权平均值图
Figure 6. U-Pb concordia diagrams of the zircons and weighted mean 206Pb/238U age from the granodiorite
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图 7 花岗闪长岩R1-R2 (a)、SiO2-TFeO/(TFeO+MgO)(b)、（Yb+Ta）-Rb(c)和（Y+Nb）-Rb(d)图解
①—地幔斜长花岗岩；②—破坏性活动板块边缘(板块碰撞前)花岗岩; ③—板块碰撞后隆起期花岗岩；④—晚造期花岗岩；⑤—非造山区A型花岗岩；⑥—同碰撞(S型)花岗岩；⑦—造山期后A型花岗岩; IAG—岛弧花岗岩类；CAG—大陆弧花岗岩类；CCG—大陆碰撞花岗岩类；POG—后造山花岗岩类；RRG—与裂谷有关的花岗岩类；CEUG—与大陆的造陆抬升有关的花岗岩类
Figure 7. R1-R2(a), SiO2-TFeO/(TFeO+MgO)(b), (Yb+Ta) -Rb(c) and (Y+Nb) -Rb(d) diagrams of the granodiorite
表 1 石底泉地区花岗闪长岩主量、微量和稀土元素分析结果
Table 1 Content of major, trace and rear earth elements of the granodiorite in Shidiquan area
样号 D1392-YQ1 D1392-YQ2 D1392-YQ3 SiO2 69.28 69.85 70.85 TiO2 0.25 0.26 0.24 Al2O3 11.76 11.76 11.75 Fe2O3 0.15 0.06 0.24 FeO 1.96 2.18 1.74 MnO 0.07 0.07 0.07 MgO 1.12 1.20 1.03 CaO 3.67 3.75 3.59 Na2O 3.12 3.11 3.12 K2O 3.68 3.57 3.78 P2O5 0.07 0.07 0.07 烧失量 3.17 3.39 2.95 总量 98.29 99.29 99.43 A/CNK 0.75 0.74 0.75 Rb 110.06 104.24 115.88 Sr 158.91 153.70 164.12 Ba 747.11 745.87 748.35 Th 14.41 16.75 12.06 U 1.82 1.92 1.71 Nb 11.18 11.25 11.10 Ta 0.69 0.60 0.77 Zr 120.13 137.13 103.13 Hf 1.48 1.66 1.30 La 26.92 26.56 27.27 Ce 47.42 48.60 46.24 Pr 5.78 5.89 5.66 Nd 20.63 20.90 20.36 Sm 4.44 4.60 4.28 Eu 0.93 1.02 0.84 Gd 4.27 4.39 4.14 Tb 0.67 0.71 0.63 Dy 3.66 3.82 3.50 Ho 0.74 0.74 0.73 Er 2.10 2.10 2.10 Tm 0.31 0.30 0.31 Yb 1.94 2.10 1.77 Lu 0.29 0.26 0.31 Y 18.34 18.78 17.89 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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表 2 研究区花岗闪长岩锆石U-Th-Pb同位素分析结果
Table 2 Results of zircon U-Th-Pb isotope analysis of the granodiorite in the study area
测点编号 元素含量/10-6 Th/
U同位素比值 年龄/Ma Pb Th U 207Pb/206Pb 207Pb/235U 206Pb238U 207Pb/206Pb 207Pb/235U 206Pb/238U 谐和度 测值 1σ 测值 1σ 测值 1σ 测值 1σ 测值 1σ 测值 1σ D1392-01 182 460 874 0.53 0.0696 0.0012 1.3932 0.0251 0.1449 0.0010 917 36 886 11 872 6 98% D1392-02 110 548 1009 0.54 0.0578 0.0016 0.5695 0.0152 0.0716 0.0010 520 63 458 10 446 6 97% D1392-03 243 255 1530 0.17 0.0695 0.0009 1.3877 0.0213 0.1444 0.0014 915 19 884 9 869 8 98% D1392-04 394 407 2510 0.16 0.0689 0.0009 1.3904 0.0278 0.1462 0.0024 894 29 885 12 880 14 99% D1392-05 167 443 2040 0.22 0.0571 0.0009 0.5669 0.0101 0.0718 0.0007 494 35 456 7 447 4 98% D1392-06 204 632 2319 0.27 0.0570 0.0008 0.5682 0.0088 0.0720 0.0006 494 31 457 6 448 3 98% D1392-07 307 325 1920 0.17 0.0698 0.0009 1.3927 0.0205 0.1443 0.0012 924 26 886 9 869 7 98% D1392-08 220 907 2187 0.41 0.0575 0.0010 0.5707 0.0104 0.0719 0.0007 522 39 458 7 448 4 97% D1392-09 83 34 1190 0.03 0.0576 0.0017 0.5646 0.0182 0.0709 0.0008 517 69 455 12 441 5 97% D1392-10 126 574 1239 0.46 0.0616 0.0014 0.6011 0.0136 0.0708 0.0007 661 49 478 9 441 4 91% D1392-11 221 372 1219 0.31 0.0703 0.0011 1.3879 0.0263 0.1431 0.0017 937 31 884 11 862 10 97% D1392-12 239 312 1411 0.22 0.0702 0.0010 1.3886 0.0243 0.1432 0.0016 1000 30 884 10 863 9 97% D1392-13 109 486 1041 0.47 0.0587 0.0015 0.5743 0.0154 0.0708 0.0007 554 56 461 10 441 4 95% D1392-14 315 311 2041 0.15 0.0709 0.0009 1.3899 0.0221 0.1420 0.0016 967 25 885 9 856 9 96% D1392-15 194 380 972 0.39 0.0700 0.0012 1.3860 0.0258 0.1437 0.0018 929 35 883 11 866 10 98% D1392-16 164 785 1493 0.53 0.0578 0.0011 0.5678 0.0146 0.0711 0.0012 520 41 457 9 443 7 96% D1392-17 261 521 1297 0.40 0.0692 0.0010 1.3849 0.0252 0.1448 0.0016 903 28 883 11 872 9 98% D1392-18 272 1020 2710 0.38 0.0605 0.0009 0.5914 0.0091 0.0708 0.0005 620 30 472 6 441 3 93% D1392-19 120 199 626 0.32 0.0684 0.0010 1.3807 0.0213 0.1461 0.0010 883 35 881 9 879 6 99% D1392-20 287 863 3159 0.27 0.0562 0.0009 0.5538 0.0088 0.0714 0.0005 457 31 447 6 445 3 99% D1392-21 151 821 1261 0.65 0.0598 0.0011 0.5807 0.0121 0.0703 0.0008 594 41 465 8 438 5 94% D1392-22 325 1475 2952 0.50 0.0618 0.0010 0.5961 0.0083 0.0703 0.0007 665 33 475 5 438 4 91% D1392-23 171 372 810 0.46 0.0696 0.0012 1.3804 0.0276 0.1436 0.0018 917 33 881 12 865 10 98% D1392-24 200 226 1190 0.19 0.0699 0.0010 1.3907 0.0254 0.1442 0.0019 924 30 885 11 868 11 98% D1392-25 260 385 1402 0.27 0.0691 0.0011 1.3874 0.0250 0.1456 0.0018 902 27 884 11 876 10 99% 注：所列误差均为1σ；样品测试单位为西北大学大陆动力学国家重点实验室
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