Zircon U-Pb ages, geochemical characteristics and geo-logical significance of Yaganbuyang gneiss in Qingbaikou period along the Altun orogenic belt
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摘要:
出露于阿中地块库木塔什萨依一带的亚干布阳片麻岩主要岩性为黑云斜长片麻岩、黑云二长片麻岩。利用LA-ICPMS方法进行锆石微区U-Pb同位素定年，得到206Pb/238U年龄加权平均值为900.2±2.9Ma，表明亚干布阳片麻岩原岩形成于新元古代早期青白口纪；地球化学结果显示，主量元素具有高SiO2、Al2O3、K2O+Na2O含量，低Na2O、MgO、CaO和TiO2含量的特征，A/CNK值介于0.95~1.22之间，属于高钾钙碱性系列的过铝质花岗岩。岩石富集Rb、Th、K等大离子亲石元素，亏损Nb、Sr、P、Hf、Ti等高场强元素；岩石轻稀土元素分馏较强而重稀土元素分馏较弱，具有明显的负Eu异常，总体呈右倾的“Ⅴ”字形稀土元素配分模式，显示典型的地壳重熔型花岗岩特征。亚干布阳片麻岩的源岩主要为地壳中沉积岩类的部分熔融，形成于俯冲-同碰撞构造环境。综上说明亚干布阳片麻岩是新元古代早期俯冲碰撞热事件的产物，反映阿中地块和柴达木地块青白口纪处于汇聚碰撞阶段，构造岩浆活动强烈，与Rodinia超大陆汇聚事件具有一致性。
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关键词:
- 亚干布阳片麻岩 /
- LA-ICP-MS锆石U-Pb定年 /
- 地球化学 /
- 罗迪尼亚超大陆 /
- 阿尔金
Abstract:The Yaganbuyan gneiss is outcropped in the Kumutashisayi area of the Azhong Block. The gneiss rocks are composed mainly of biotite plagioclase gneiss and biotite monzonitic gneiss. The U-Pb dating of zircons from the gneiss using LA-ICP-MS yielded an age of 900.2 ±2.9Ma, which indicates that Yaganbuyan gneiss was generated in Early Neoproterozoic. Geochemical analy-sis shows that major elements are characterized by high SiO2, Al2O3 and K2O+Na2O content, and low Na2O, MgO, CaO and TiO2 content, with A/CNK being 0.95~1.22, suggesting that the granite belongs to the typical high-K calc-alkaline series with peralumi-nous nature. The gneisses are enriched in large ion lithophile elements of Rb, Th, K and depleted in high field strength elements of Nb, Sr, P, Hf, Ti. These characteristics are similar to features of the continental collision type granite. REE distribution patterns show negative anomaly of Eu and distinct enrichment of LREE relative to HREE. The chondrite-normalized REE patterns are right-in-clined, with a clear Ⅴ trough. The source rock of the gneiss was mainly from the partial melting of sedimentary rocks in the crust and generated in a subduction-collisional environment. These features indicate that the Yaganbuyan gneiss was formed in the Neopro-terozoic, and that a subductional collision event took place in the Qaidam microplate and the Azhong plate, which coincides with the assembly event of the supercontinent Rodinia.
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Key words:
- Yaganbuyan gneiss /
- LA-ICP-MS zircon U-Pb dating /
- geochemistry /
- Rodinia supercontinent /
- Alun
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表 1 亚干布阳片麻岩(样品PM003-11) LA-ICP-MS锆石U-Th-Pb同位素分析结果
Table 1. LA-ICP-MS zircon U-Th-Pb isotopic analyses of Yaganbuyang gneiss(sample PM003-11)
点号 Th/
U同位素比值 年龄/Ma 207Pb/
206Pb1σ 207Pb/
235U1σ 206Pb/
238U1σ 208Pb/
232Th1σ 207Pb/
206U1σ 207Pb/
235U1σ 206Pb/
238Th1σ 208Pb/
232Th1σ 01 0.37 0.07287 0.0017 1.502 0.01881 0.1496 0.00137 0.04434 0.00047 1010 46 931 8 899 8 877 9 02 0.48 0.07402 0.00164 1.5351 0.01579 0.1505 0.00133 0.04529 0.00039 1042 44 945 6 904 7 895 8 03 0.23 0.0755 0.00182 1.56755 0.02218 0.15066 0.00142 0.04619 0.00066 1082 48 958 9 905 8 913 13 04 0.61 0.07716 0.00178 1.58381 0.01937 0.14894 0.00136 0.04588 0.00044 1125 45 964 8 895 8 907 8 05 0.43 0.07338 0.00164 1.50659 0.01674 0.14896 0.00134 0.04456 0.00041 1025 45 933 7 895 8 881 8 06 0.31 0.07498 0.00166 1.55528 0.01668 0.1505 0.00134 0.04863 0.00045 1068 44 953 7 904 8 960 9 07 0.36 0.07397 0.00163 1.53618 0.0164 0.15065 0.00135 0.0453 0.00042 1041 44 945 7 905 8 896 8 08 0.33 0.07279 0.00273 1.4987 0.04774 0.14935 0.00199 0.04425 0.00129 1008 74 930 19 897 11 875 25 09 0.41 0.07103 0.00165 1.46069 0.01921 0.14915 0.00139 0.04153 0.00046 958 47 914 8 896 8 822 9 10 0.34 0.07048 0.00294 1.05167 0.03843 0.10822 0.00152 0.04075 0.00133 942 83 730 19 662 9 807 26 11 0.31 0.07293 0.00159 1.51547 0.01582 0.1507 0.00135 0.04552 0.00042 1012 43 937 6 905 8 900 8 12 0.32 0.07529 0.00163 1.55132 0.01625 0.14942 0.00134 0.04821 0.00044 1076 43 951 6 898 8 952 9 13 0.41 0.07345 0.00157 1.52527 0.01556 0.15057 0.00135 0.04583 0.0004 1026 43 941 6 904 8 906 8 14 0.35 0.07087 0.00189 1.47007 0.02761 0.1504 0.00155 0.04464 0.00071 954 54 918 11 903 9 883 14 15 0.37 0.07156 0.00153 1.48314 0.01535 0.15027 0.00135 0.0452 0.00041 973 43 924 6 903 8 894 8 16 0.47 0.07736 0.00167 1.60998 0.01725 0.15088 0.00136 0.04908 0.00044 1131 42 974 7 906 8 968 9 17 0.30 0.07127 0.00158 1.4785 0.0177 0.15039 0.00138 0.04589 0.0005 965 45 922 7 903 8 907 10 18 0.34 0.06996 0.00149 1.44591 0.01501 0.14983 0.00135 0.04451 0.00041 927 43 908 6 900 8 880 8 19 0.01 0.06056 0.00418 0.53554 0.03495 0.0641 0.00121 0.37075 0.04918 624 142 436 23 401 7 6374 725 20 0.38 0.07105 0.00153 1.46619 0.01627 0.14959 0.00136 0.04507 0.00044 959 43 917 7 899 8 891 8 21 0.34 0.07168 0.0015 1.4754 0.0149 0.14922 0.00134 0.04684 0.00042 977 42 920 6 897 8 925 8 22 0.01 0.0571 0.00639 0.50629 0.05498 0.06427 0.00179 0.2096 0.04759 495 230 416 37 402 11 3846 795 23 0.60 0.07831 0.00168 1.60843 0.01792 0.14889 0.00136 0.04978 0.00047 1155 42 974 7 895 8 982 9 24 0.36 0.08287 0.00173 1.71677 0.01731 0.15017 0.00136 0.06023 0.00054 1266 40 1015 6 902 8 1182 10 25 0.70 0.07706 0.00176 1.58798 0.02224 0.14939 0.00144 0.0439 0.00047 1123 45 966 9 898 8 868 9 26 0.42 0.0708 0.00146 1.47026 0.0148 0.15054 0.00136 0.04402 0.00039 952 42 918 6 904 8 871 8 27 0.43 0.06884 0.00145 1.42215 0.01552 0.14975 0.00137 0.04434 0.00042 894 43 898 7 900 8 877 8 28 0.41 0.06886 0.00143 1.41493 0.01495 0.14897 0.00136 0.04108 0.00039 894 42 895 6 895 8 814 7 29 0.47 0.07157 0.00147 1.46948 0.01504 0.14885 0.00135 0.04702 0.00042 974 41 918 6 895 8 929 8 30 0.38 0.06662 0.00137 1.37652 0.01399 0.14979 0.00136 0.04493 0.00041 826 42 879 6 900 8 888 8 
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表 2 亚干布阳片麻岩主量、微量和稀土元素分析结果
Table 2. Major, trace and REE contents of the Yaganbuyang gneiss
样品号 SiO2 TiO2 Al2O3 Fe2O3 FeO MgO MnO CaO Na2O K2O PM030/20-1 66.33 0.70 15.28 0.86 4.45 0.09 1.50 3.38 2.84 2.81 PM030/21-1 67.62 0.47 14.25 1.17 2.77 0.07 1.44 2.79 3.11 4.42 PM030/22-1 68.39 0.58 14.97 0.71 3.61 0.08 1.07 1.96 2.36 4.49 PM030/23-1 67.72 0.59 14.62 0.74 3.80 0.07 1.13 2.24 2.28 4.70 PM030/26-1 66.66 0.71 15.47 0.83 4.62 0.08 1.38 3.20 2.80 2.71 样品号 P2O5 烧失量 总计 AR σ A/NK A/CNK K2O+Na2O Na2O/K2O Mg# PM030/20-1 0.14 0.91 99.29 1.88 1.37 1.98 1.10 5.65 1.01 33.84 PM030/21-1 0.09 1.32 99.52 2.15 2.30 1.44 0.95 7.53 0.70 40.16 PM030/22-1 0.15 1.10 99.47 1.77 1.85 1.71 1.22 6.85 0.53 30.99 PM030/23-1 0.14 1.42 99.45 1.74 1.97 1.65 1.13 6.98 0.49 31.10 PM030/26-1 0.14 0.70 99.30 1.86 1.28 2.05 1.16 5.51 1.03 31.44 样品号 La Ce Pr Nd Sm Eu Gd Tb Dy Ho PM030/20-1 57.4 116 15 56 10 1.42 8.94 1.19 6.37 1.15 PM030/21-1 35.5 72 7.4 27.7 4.74 0.94 5.32 0.71 5 0.92 PM030/22-1 39.4 84.7 9.35 36.6 7.26 0.96 7.44 1.02 6.73 1.18 PM030/23-1 40.7 86.4 9.34 37 7.28 1.16 7.19 0.94 5.92 0.99 PM030/26-1 43.2 85.1 11 41.12 7.39 1.52 6.85 0.963 5.34 1.02 样品号 Yb Lu Y ∑REE LREE HREE LREE/
HREEδEu δCe （La/Yb）N PM030/20-1 3.24 0.52 33.40 314.36 255.82 58.54 4.37 0.45 0.91 11.97 PM030/21-1 3.34 0.45 30.70 198.25 148.28 49.97 2.97 0.57 1.00 7.18 PM030/22-1 3.32 0.45 36.00 238.41 178.27 60.14 2.96 0.40 1.01 8.02 PM030/23-1 2.61 0.34 30.40 233.59 181.88 51.71 3.52 0.48 1.01 10.54 PM030/26-1 3.01 0.49 29.70 240.07 189.33 50.74 3.73 0.64 0.90 9.70 样品号 Rb Ba Th U Ta Nb Sr Nd Zr Hf PM030/20-1 161.40 645.20 15.60 3.81 0.35 15.00 150.30 56.00 204.20 5.32 PM030/21-1 152.10 600.60 25.90 2.16 0.79 11.50 193.40 27.70 151.50 2.61 PM030/22-1 236.60 434.00 21.40 3.12 2.60 15.70 90.80 36.60 182.70 2.40 PM030/23-1 174.20 672.10 24.80 2.52 1.33 18.40 136.10 37.00 175.60 1.33 PM030/26-1 153.00 595.00 14.90 3.22 0.33 14.80 153.00 41.12 195.00 5.30 注：样品PM030/20-1、PM030/21-1、PM030/26-1为黑云斜长片麻岩；PM030/22-1、PM030/23-1为黑云二长片麻岩；主量元素含量单位为%，微量和稀土元素含量为10-6
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② 中国地质调查局西安地质调查中心. 新疆1: 5万阿尔金山清水泉地区四幅区调查成果报告. 2010.
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