New progress in the study of Gongyanghe Group in southern Baoshan block, western Yunnan Province
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摘要:
保山地块是滇西特提斯多岛洋的重要组成部分,属滇-缅-马-泰微大陆的北端。出露的最老地层被称为公养河群,主要分布于保山地块南部酒房-旧城-大汪塘和镇安街-绕廊街-公养河-芒海-瑞丽2个片区,为一套厚度巨大的砂岩、长石石英砂岩-砂质板岩-泥质板岩组合,夹硅质岩、泥质硅质岩、薄层灰岩,具有典型的浊流沉积特征,部分地段有低级变质现象。公养河群中生物化石稀少,缺乏年代学依据,其时代被推测为震旦纪-中寒武世。近年来的1:25万、1:5万区域地质调查项目对公养河群进行了深入研究,在新发现的中酸性火山熔岩、凝灰岩夹层中获得了一批可靠的LA-ICP-MS锆石U-Pb年龄(925.0±9.2~499.2±2.1Ma)。结合岩性组合、沉积环境的差异,建议将公养河群自下而上细分为青白口-南华系大汪塘组、震旦系-中寒武统公养河组、上寒武统-奥陶系蒲满哨组3个组级岩石地层单元。主要介绍大汪塘组的分布、岩性组合、沉积环境、时代依据。
Abstract:Located at the northern end of the Yunnan-Myanmar-Malaysia-Thailand microcontinent, the Baoshan block is an important part of multi-island ocean in Paleozoic Tethys, western Yunnan Province. The oldest exposed stratum is known as the Gongyanghe Group on the Baoshan block. It is mainly exposed in two areas, i.e., Jiufang-Jiucheng-Dawangtang and Zhen'anjie-Raolangjie-Gongyanghe-Manhai-Ruili. It is a lithological association with huge thickness, consisting of sandstone, feldspar quartz sandstone, sandy slate and muddy slate, intercalated with siliceous rocks, argillaceous siliceous rocks, thin limestone, with the typical turbidity sedimentary characteristics and some low grade metamorphic features. Few fossils exist in the Gongyanghe Group, causing the lack of the chronological information, and hence its geological time was previously inferred to be Sinian to Middle Cambrian. In recent years, 1:250000 and 1:50000 regional geological survey conducted further research on Gongyanghe Group. A number of reliable LA-ICP-MS zircon U-Pb ages (925.0±9.2~500.0±1.0Ma) were obtained from newly discovered intermediate-acid volcanic lava and tuff interlayer. Combined with the differences of lithological association and sedimentary environment, it is suggested that Gongyanghe Group should be subdivided into 3 formations from bottom to top, namely Qingbaikou to Nanhua System Dawangtang Formation, Sinian-Middle Cambrian Gongyanghe Formation, and Early Cambrian-Ordovician Pumanshao Formation. This paper mainly describes the distribution, lithological association, sedimentary environment and geological epoch of the Dawangtang Formation.
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Key words:
- Baoshan block /
- Gongyanghe Group /
- Dawangtang Formation /
- zircon U-Pb ages
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表 1 大汪塘凝灰岩、流纹岩LA-ICP-MS锆石U-Th-Pb同位素分析数据
Table 1. LA-ICP-MS zircon U-Th-Pb isotopic analytical results of tuff and rhyolite from Dawangtang
锆石编号 元素含量/10-6 232Th/238U 同位素比值 年龄/Ma 206Pb 207Pb 208Pb 232Th 238U 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 208Pb/232Th 1σ 207Pb/206Pb 1σ 207Pb/235U 1σ 206Pb/238U 1σ 208Pb/232Th 1σ 凝灰岩(D007) D007-1 105 26.3 72.2 71.6563 168.9811 0.42 0.07022 0.00118 1.54125 0.02919 0.15922 0.00206 0.10605 0.00629 935 29 947 12 952 11 2037 115 D007-2 41.4 11.0 19.8 16.0297 62.8223 0.26 0.07576 0.00261 1.61418 0.05814 0.15488 0.00321 0.13238 0.00958 1089 60 976 23 928 18 2513 171 D007-3 126 30.7 79.3 80.4011 205.1132 0.39 0.06756 0.0012 1.43182 0.03042 0.15352 0.00202 0.14461 0.01026 855 35 902 13 921 11 2730 181 D007-4 72.3 18.0 88.4 82.5218 108.6238 0.76 0.07032 0.00157 1.48512 0.03423 0.15361 0.00213 0.18156 0.01411 938 39 924 14 921 12 3372 241 D007-5 163 41.1 130 132.1459 291.6048 0.45 0.07077 0.00129 1.54652 0.03745 0.15849 0.00283 0.20482 0.0162 951 34 949 15 948 16 3766 272 D007-6 58.8 14.6 41.3 21.6171 83.9071 0.26 0.06982 0.00168 1.49885 0.03812 0.15601 0.00236 0.1781 0.01405 923 43 930 15 935 13 3313 241 D007-7 87.5 22.3 95.8 89.2643 138.9721 0.64 0.0721 0.00129 1.5923 0.03366 0.16033 0.00248 0.15443 0.01101 989 30 967 13 959 14 2903 193 D007-8 48.2 12.1 45.2 53.4107 91.0493 0.59 0.07203 0.00142 1.50056 0.02908 0.15178 0.00209 0.11642 0.00758 987 28 931 12 911 12 2226 137 D007-9 26.9 7.16 33.0 31.8882 44.2257 0.72 0.07156 0.00187 1.49792 0.04754 0.15072 0.00225 0.09669 0.00547 973 58 930 19 905 13 1866 101 D007-10 68.0 17.0 64.9 59.7428 105.3733 0.57 0.07037 0.00145 1.53924 0.03423 0.15821 0.00196 0.04753 0.00082 939 39 946 14 947 11 939 16 D007-11 45.4 10.9 36.7 36.7151 75.5737 0.49 0.06978 0.0014 1.47795 0.03094 0.15343 0.00185 0.04525 0.00077 922 36 921 13 920 10 895 15 D007-12 58.6 14.9 84.2 92.6872 98.4853 0.94 0.07243 0.00146 1.55564 0.03476 0.15556 0.00227 0.0453 0.00075 998 35 953 14 932 13 895 14 D007-13 95.1 23.0 97.1 93.0429 133.7704 0.70 0.07091 0.00123 1.48002 0.0242 0.15182 0.00206 0.04342 0.00058 955 19 922 10 911 12 859 11 D007-14 90.1 21.6 72.9 62.7348 133.1195 0.47 0.06891 0.0012 1.44786 0.03017 0.15168 0.00183 0.0454 0.00069 896 36 909 13 910 10 897 13 D007-15 180 43.8 167 174.8778 312.0432 0.56 0.06843 0.00099 1.44079 0.02699 0.15244 0.00228 0.04424 0.00068 882 24 906 11 915 13 875 13 D007-16 85.9 22.3 83.4 115.9802 203.3275 0.57 0.06806 0.00103 1.40579 0.0239 0.14944 0.00165 0.0448 0.00063 870 27 891 10 898 9 886 12 D007-17 97.4 25.0 40.4 39.1472 161.4160 0.24 0.07183 0.00104 1.58387 0.03145 0.1593 0.00213 0.04612 0.00078 981 31 964 12 953 12 911 15 D007-18 108 30.5 98.0 84.0635 183.1318 0.46 0.07163 0.00435 1.50361 0.08851 0.15224 0.00225 0.04608 0.00068 975 127 932 36 914 13 911 13 D007-19 38.6 9.62 40.9 40.0219 61.4038 0.65 0.0696 0.00164 1.5136 0.03632 0.15826 0.00236 0.04374 0.0008 916 40 936 15 947 13 865 16 流纹岩(D594) D594-1 151.7 11 11.18 133.22 268.61 0.50 0.06553 0.00224 1.21507 0.02859 0.13445 0.00234 0.04213 0.00073 792 70 808 13.1 813.2 13 834.1 14.22 D594-2 61.96 4.65 8.85 111.66 109.62 1.02 0.06773 0.00267 1.25609 0.03834 0.13447 0.00248 0.03978 0.00072 860 79.8 826 17.3 813.3 14 788.5 14.06 D594-3 153.9 11.1 16.24 221.8 275.01 0.81 0.06522 0.0022 1.19659 0.02742 0.13304 0.00231 0.03674 0.00058 781 69.3 799 12.7 805.2 13 729.3 11.33 D594-4 147.3 10.8 8.8 109.98 258.79 0.42 0.06643 0.00229 1.23505 0.02955 0.13482 0.00236 0.04011 0.00075 820 70.3 817 13.4 815.3 13 794.8 14.52 D594-5 109.2 8.13 20.77 325.71 191.35 1.70 0.06736 0.0023 1.25299 0.02944 0.13488 0.00235 0.03194 0.00047 849 69.4 825 13.3 815.6 13 635.6 9.26 D594-6 77.09 5.62 12.05 151.67 136.08 1.11 0.06603 0.0024 1.21742 0.03232 0.13369 0.00238 0.03975 0.00064 807 74.4 809 14.8 808.9 14 788 12.53 D594-7 145.7 11 7.22 98.08 255.22 0.38 0.06845 0.00226 1.27039 0.0279 0.13458 0.00233 0.03685 0.00066 882 67 833 12.5 813.9 13 731.4 12.85 D594-8 361.5 27 11.15 131.57 629.89 0.21 0.06773 0.00213 1.25446 0.02435 0.13431 0.00229 0.04229 0.00072 860 63.9 825 11 812.4 13 837.1 13.97 D594-9 183.2 13.6 11.63 133.09 313.14 0.43 0.06784 0.00227 1.25715 0.02809 0.13438 0.00234 0.04312 0.00074 864 67.8 827 12.6 812.8 13 853.2 14.41 注:由西北大学大陆动力学国家重点实验室测试,2014 表 2 凝灰岩LA-ICP-MS锆石U-Th-Pb同位素分析数据
Table 2. LA-ICP-MS zircon U-Th-Pb isotopic analytical results of tuff
锆石编号 元素含量/10-6 232Th/238U 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th 207Pb/206Pb 207Pb/235U 206Pb/238U 208Pb/232Th Pb Pb 232Th 238U 比值 1σ 比值 1σ 比值 1σ 比值 1σ 年龄 1σ 年龄 1σ 年龄 1σ 年龄 1σ D250-1 1.54 80.8 274 433 0.63 0.0680 0.0026 1.3523 0.0501 0.1422 0.0019 0.0392 0.0013 878 78.55 869 21.6 857 10.9 777 25.6351 D250-2 1.58 65.8 213 381 0.56 0.0649 0.0028 1.2698 0.0500 0.1387 0.0025 0.0467 0.0021 772 90.73 832 22.4 837 14 923 39.774 D250-3 0.79 13.52 66.1 74.2 0.89 0.0663 0.0041 1.2579 0.0748 0.1355 0.0027 0.0416 0.0018 817 127.8 827 33.7 819 15.1 823 34.0644 D250-4 0.82 23.29 63.1 131 0.48 0.0704 0.0031 1.4026 0.0584 0.1427 0.0022 0.0418 0.0015 940 86.58 890 24.7 860 12.7 828 29.7789 D250-5 0.36 29.38 92.5 168 0.55 0.0665 0.0030 1.2866 0.0578 0.1385 0.0021 0.0382 0.0013 833 93.36 840 25.7 836 11.6 757 25.8159 D250-6 0.019 90.7 930 369 2.52 0.0646 0.0027 1.2316 0.0485 0.1349 0.0020 0.0402 0.0013 761 61.11 815 22.1 816 11.4 797 25.3684 D250-7 0.00 70.5 517 360 1.43 0.0694 0.0027 1.3230 0.0530 0.1364 0.0024 0.0340 0.0012 909 81.48 856 23.2 824 13.8 675 23.181 注:由武汉上谱分析科技有限责任公司测试完成,2017 -
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