LA-ICP-MS U-Pb geochronology of detrital zircons from the Gudongjing Complex-Group in Pantuoshan area of Beishan region within Inner Mongolia during Changchengian Period and its geological significance
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摘要:
长城纪古硐井群作为内蒙古北山地区古老褶皱基底之上的第一个沉积盖层，尚未获得可靠的年龄资料，前人只是根据其产出的层位和岩石组合特征与燕山地区的长城系对比后，将其置于中元古代长城纪。对古硐井群变质长石石英砂岩中碎屑锆石进行了LA-ICP-MS U-Pb测年，结果显示，锆石207Pb/206Pb年龄数据90%介于1.3~2.2Ga之间，其余年龄介于2.4~3.2Ga之间，峰期在1.6~2.0Ga之间，最年轻的碎屑锆石207Pb/206Pb年龄为1393±50Ma。通过对比碎屑锆石的年龄频谱和周围古地块的形成时代，碎屑锆石的U-Pb年龄限制了古硐井群的沉积时代，应为中元古代蓟县纪，古硐井群的沉积物可能来自北山-阿拉善和塔里木-敦煌地块。
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关键词:
- 碎屑锆石 /
- LA-ICP-MS U-Pb年龄 /
- 古硐井群 /
- 内蒙古北山 /
- 盘陀山
Abstract:Changchengian Period Gudongjing Complex-Group serves as the first sedimentary cover on the ancient folded base-ment in Beishan region of Inner Mongolia, but without reliable dating data. Previous researchers assigned it to Mesoproterozoic Changchengian Period only on the basis of the contrast with the Changchengian system of the Yanshan area in such aspects as for-mation layers and rock association characteristics. In this paper, the LA-ICP-MS zircon U-Pb method was used for the determi-nation of the age of the detrital zircon in metamorphic quartz sandstone of the Gudongjing Complex-Group, and the test results show that the 90% ages of zircon 207Pb/206Pb data are 1.3~2.2Ga, the rest of ages are 2.4~3.2Ga, peak period ages are 1.6~2.0Ga, and the youngest 207Pb/206Pb age of detrital zircon is 1393±50Ma. Based on comparing the age spectrum of the detrital zircon with the formation age of the surrounding massif, the dertital zircon limits the sedimentary age of the Gudongjing Complex-Group as the Mesoproterozoic Jixianian Period. The sediments of the Gudongjing Complex-Group might have come from Beishan-Alxa and Tarim-Dunhuang blocks.
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致谢: 河北省区域地质矿产调查研究所胡醒民教授级高级工程师和中国地质科学院地质研究所李锦轶研究员对本文提出了宝贵的修改意见，在此表示诚挚的谢意。
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图 1 北山地区构造格架简图[7]（a）和研究区地质简图（b）
Ⅰ—红石山-百合山-蓬勃山蛇绿岩带；Ⅱ—芨芨台子-小黄山蛇绿岩带；Ⅲ—红柳河月牙山洗肠井蛇绿岩带；Ⅳ—辉铜山-帐房山蛇绿岩带
Figure 1. Tectonic framework sketch map of the Beishan area (a) and simplified geological map of the study area (b)
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图 2 古硐井群变质长石石英砂岩野外（a）及显微（b）照片
Figure 2. Field photo (a) and microphotograph (b) of metamorphic quartz sandstone in the Gudongjing Complex-Group
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图 3 古硐井群变质长石石英砂岩碎屑锆石阴极发光图像
Figure 3. Cathodoluminescene images of detrital zircons from metamorphic quartz sandstone of the Gudongjing Complex-Group
表 1 古硐井群变质长石石英砂岩碎屑锆石LA-ICP-MS U-Th-Pb同位素测年结果
Table 1 The results of detrital zircon LA-ICP-MS U-Th-Pb dating of metamorphic quartz sandstone from the Gudongjing Complex-Group in Beishan area, Inner Mongolia
点号 Pb/10-6 U/10-6 206Pb/238U 207Pb/235U 207Pb/206Pb 207Pb/206Pb Th/U 比值 1σ 比值 1σ 比值 1σ 年龄/Ma 1σ 1 78 784 0.0908 0.0024 1.2255 0.0509 0.0977 0.0024 1581 46 0.95 3 44 133 0.2549 0.0025 3.3912 0.0965 0.0965 0.0025 1558 48 1.17 4 67 209 0.2619 0.0043 4.1302 0.1112 0.1145 0.0029 1872 46 0.79 5 110 391 0.2437 0.0030 3.3274 0.0863 0.0991 0.0022 1606 42 0.80 6 160 448 0.3019 0.0032 4.6451 0.1194 0.1116 0.0025 1826 41 0.79 7 91 276 0.2936 0.0051 4.4209 0.1296 0.1092 0.0025 1786 41 0.60 8 102 358 0.2174 0.0027 4.0829 0.1293 0.1362 0.0037 2179 48 1.26 9 128 342 0.3169 0.0041 4.9805 0.1332 0.1140 0.0026 1864 41 0.93 10 116 495 0.1987 0.0034 2.8923 0.0795 0.1057 0.0031 1727 53 0.97 11 105 426 0.2479 0.0032 3.3288 0.0894 0.0974 0.0022 1575 43 0.18 12 73 265 0.2338 0.0073 2.9790 0.1203 0.0924 0.0022 1476 45 0.92 13 120 544 0.2041 0.0032 2.9964 0.0811 0.1065 0.0025 1740 43 0.90 14 211 871 0.2217 0.0019 2.8171 0.0724 0.0921 0.0021 1470 44 0.59 15 65 262 0.2060 0.0022 3.0808 0.1020 0.1084 0.0032 1773 54 0.95 16 66 279 0.2086 0.0043 2.8189 0.0797 0.0981 0.0024 1588 46 0.74 17 100 370 0.2310 0.0022 2.8791 0.0734 0.0904 0.0021 1434 44 1.07 18 37 149 0.2012 0.0067 3.1993 0.1222 0.1155 0.0030 1887 47 1.91 19 119 434 0.2362 0.0026 3.6245 0.1187 0.1113 0.0034 1821 55 1.01 20 47 155 0.2442 0.0051 3.8534 0.1113 0.1146 0.0030 1873 48 0.98 21 88 298 0.2820 0.0047 4.2922 0.1179 0.1104 0.0026 1807 42 0.32 22 70 196 0.2899 0.0030 4.8866 0.1554 0.1222 0.0032 1988 47 1.32 23 211 787 0.2332 0.0029 3.5242 0.0902 0.1097 0.0026 1794 43 0.82 24 222 1129 0.2008 0.0021 3.2569 0.0827 0.1176 0.0027 1920 40 0.06 25 35 130 0.2420 0.0025 3.2265 0.0918 0.0967 0.0027 1562 52 0.52 26 155 577 0.2433 0.0042 4.1887 0.1200 0.1251 0.0040 2030 56 0.54 27 167 626 0.2392 0.0023 3.1068 0.0762 0.0942 0.0021 1512 43 0.77 29 75 221 0.2594 0.0023 5.6698 0.3084 0.1583 0.0078 2438 84 0.80 30 149 477 0.2586 0.0059 4.3797 0.1167 0.1231 0.0031 2001 44 0.94 31 46 123 0.3138 0.0027 5.3705 0.1688 0.1241 0.0037 2016 53 0.70 32 130 408 0.2933 0.0025 4.5903 0.1129 0.1135 0.0026 1857 41 0.52 33 75 212 0.3220 0.0029 5.3400 0.1388 0.1203 0.0028 1960 41 0.46 34 188 619 0.2691 0.0024 4.0388 0.1005 0.1089 0.0025 1781 42 0.66 35 68 274 0.2033 0.0016 2.4809 0.0707 0.0885 0.0023 1393 50 1.46 36 179 1147 0.1447 0.0020 2.0297 0.0553 0.1017 0.0023 1656 42 0.99 37 34 161 0.2003 0.0054 2.9217 0.0922 0.1060 0.0029 1731 50 0.52 38 161 733 0.1696 0.0024 2.4345 0.1008 0.1039 0.0033 1696 58 1.37 39 56 213 0.2043 0.0028 3.4852 0.1413 0.1235 0.0039 2007 56 1.45 40 192 288 0.5617 0.0086 17.7007 0.5198 0.2285 0.0052 3041 36 0.52 41 53 161 0.2893 0.0070 5.1710 0.3418 0.1290 0.0058 2084 79 0.57 42 69 273 0.1996 0.0034 3.1950 0.0879 0.1162 0.0027 1898 42 1.34 43 82 360 0.2083 0.0016 2.6628 0.0734 0.0927 0.0023 1482 47 0.53 44 19 88 0.1835 0.0023 3.2904 0.1191 0.1301 0.0042 2099 57 0.54 45 48 167 0.2581 0.0025 3.9266 0.1047 0.1104 0.0029 1806 47 0.71 46 230 888 0.2643 0.002 3.8895 0.0957 0.1067 0.0024 1744 41 0.22 47 164 616 0.2437 0.0033 3.2583 0.0944 0.097 0.0022 1567 43 0.83 50 85 280 0.2872 0.0019 4.502 0.1078 0.1136 0.0025 1857 40 0.62 51 71 274 0.2096 0.002 2.5869 0.0841 0.0894 0.0026 1413 55 1.22 52 99 305 0.3085 0.0024 4.7707 0.1168 0.112 0.0026 1833 41 0.34 53 140 511 0.2413 0.0033 4.333 0.1115 0.1302 0.0033 2101 45 0.99 54 85 376 0.1997 0.0025 2.808 0.0709 0.102 0.0026 1660 48 0.96 55 156 500 0.262 0.0021 4.0431 0.0997 0.1119 0.0025 1830 41 0.83 56 77 224 0.2557 0.0027 4.6615 0.1248 0.1322 0.0031 2127 41 1.22 57 139 473 0.2319 0.0031 3.6088 0.1093 0.1128 0.0027 1845 43 0.88 58 142 209 0.475 0.004 12.9717 0.4447 0.198 0.0063 2810 52 1.08 59 48 125 0.2952 0.0029 5.0706 0.1452 0.1245 0.0031 2022 45 0.95 60 134 524 0.2198 0.0032 3.4403 0.0983 0.1135 0.0026 1855 41 0.89 61 57 202 0.2618 0.0036 4.1846 0.1165 0.1159 0.0028 1894 43 0.57 62 133 467 0.2577 0.0041 4.2701 0.1275 0.1201 0.0029 1958 43 0.6 63 77 286 0.226 0.0053 3.349 0.1002 0.1077 0.0034 1761 58 1.16 64 43 121 0.3342 0.0036 5.3079 0.1437 0.1152 0.0028 1883 43 0.41 65 102 366 0.253 0.0027 3.3648 0.085 0.0965 0.0022 1557 43 0.67 66 78 342 0.1835 0.0075 4.6039 0.1641 0.1828 0.005 2679 46 2.03 67 45 171 0.162 0.0074 5.7586 0.3066 0.2578 0.0067 3233 41 1.34 68 34 132 0.1952 0.003 3.2099 0.0909 0.1194 0.0033 1947 50 1.93 69 126 365 0.3165 0.0033 5.0471 0.1265 0.1157 0.0026 1890 41 0.53 70 50 221 0.2074 0.0018 3.39 0.0973 0.1186 0.0032 1935 49 0.56 71 158 924 0.1501 0.004 2.3078 0.0814 0.1115 0.0025 1824 41 0.91 72 51 140 0.2892 0.0043 4.2272 0.125 0.106 0.0026 1732 45 1.16 73 237 854 0.2433 0.0064 4.0918 0.1421 0.122 0.0027 1986 40 0.8 74 29 113 0.215 0.0026 3.1312 0.1 0.1056 0.0029 1724 51 0.89 75 33 182 0.1326 0.0054 3.1262 0.1063 0.1723 0.0065 2580 63 1.53 76 61 244 0.2166 0.0074 2.7503 0.1249 0.092 0.0022 1467 46 0.8 77 110 362 0.2878 0.0035 4.4238 0.1137 0.1115 0.0025 1824 41 0.36 78 98 279 0.3078 0.0028 5.2707 0.13 0.1242 0.0028 2017 40 0.57 79 27 119 0.1826 0.0052 2.8241 0.1186 0.1123 0.0037 1837 60 0.91 80 140 564 0.2039 0.0078 3.9925 0.1109 0.143 0.0056 2263 67 1.34 81 103 380 0.2468 0.0051 3.7457 0.1167 0.1101 0.0025 1801 42 0.75 82 113 341 0.2595 0.0021 3.6504 0.0929 0.102 0.0024 1661 43 1.28 83 204 658 0.2976 0.0057 5.2358 0.1374 0.1277 0.0031 2067 42 0.33 84 244 809 0.2793 0.0054 4.7449 0.1358 0.1232 0.0028 2004 40 0.58 85 42 239 0.139 0.0062 2.329 0.0964 0.1221 0.0034 1987 50 2.31 
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