LA-ICP-MS zircon U-Pb dating of monzogranite in Bayintolgoi, Gobi-Altay, Mongolia, and its geological implications
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摘要:
蒙古戈壁阿尔泰省巴音陶勒盖地区地处南戈壁-阿尔泰构造带南缘, 区内构造活动活跃, 中酸性侵入岩比较发育。采用LA-ICP-MS锆石U-Pb测年技术, 对区内二长花岗岩中的锆石进行同位素年龄研究。阴极发光图像显示, 锆石颗粒多为自形-半自形, 且有明显的初始岩浆振荡环带, 少见蚀变微区, 结合较高的Th/U值(0.65~1.79), 断定其为典型的岩浆成因锆石; 30颗锆石的206Pb/238U年龄加权平均值为300.2± 0.9Ma, 显示二长花岗岩成岩时代为晚石炭世, 代表了华力西中期的一次构造-岩浆事件, 为约束南戈壁-阿尔泰构造带晚石炭世深成岩浆活动时限提供了新证据。
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关键词:
- 二长花岗岩 /
- LA-ICP-MS锆石U-Pb年龄 /
- 南戈壁-阿尔泰 /
- 蒙古
Abstract:Bayintolgoi region in Mongolia is located in the southern South-Gobi-Altay tectonic zone. In this region, tectonic move-ment is active and intermediate-acidic intrusive rocks are well developed. Analysis of LA-ICP-MS zircon U-Pb ages was conduct-ed for zircons from monzogranite in Bayintolgoi, Mongolia. As revealed by the cathodoluminescence images, all the zircons from monzogranite are euhedral-subhedral and have oscillatory zoning, with almost all the zircons having high Th/U ratios. These charac-teristics suggest a magmatic genesis of the analyzed zircons. 30 zircons yielded a weighted mean 206Pb/238U age of 300.2± 0.9Ma. The results show that the monzogranite was formed in Upper Carboniferous and there existed a tectonic-magmatic event in the Middle Variscan. These data provide new evidence for the Upper Carboniferous orogeny in South-Gobi-Altay tectonic zone.
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Keywords:
- monzogranite /
- LA-ICP-MS zircon U-Pb ages /
- South-Gobi-Altay /
- Mongolia
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致谢: 在中国地质调查局天津地质调查中心实验过程和后期数据处理中，得到同位素实验室耿建珍高级工程师和王家松工程师的悉心指导和热情帮助；蒙古野外路线地质调查期间，得到蒙古矿产资源管理局地质调查局、地质信息中心Deegir D、Enkhbat T、Oyuntuya N工程师等的支持和帮助，谨此一致表达衷心的感谢。
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图 1 蒙古巴音陶勒盖一带大地构造简图（a）及地质图（b）（据参考文献[1, 3]修改）
Qph—更新统-全新统；Qp—更新统；N2—上新统；E3—渐新统；K2—上白垩统；C1nn—Noyonuul组；D1ul—Ulgii组；1—花岗岩；2—花岗闪长岩；3—闪长岩；4—辉长岩；5—正长花岗岩；6—二长花岗岩；7—断裂；8—整合界线；9—不整合界线；10—采样位置。Ⅰ-3-1—萨吾尔-二台-Hrairhan弧盆带；Ⅰ-3-2—洪古勒楞-阿尔曼太-Baitag弧盆带；Ⅰ-3-3—谢米斯台-库兰喀孜干弧盆带；Ⅰ-3-4—三塘湖弧盆带；Ⅰ-3-5—唐巴勒-喀拉麦里缝合带；Ⅰ-5-1—南戈壁-阿尔泰构造带
Figure 1. Tectonic sketch map （a）and geological map （b）of Bayintolgoi, Mongolia
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图 2 蒙古巴音陶勒盖地区二长花岗岩野外露头（a）和手标本（b）
Figure 2. The outcrop(a) and specimen(b) of monzogranite in Bayintolgoi, Mongolia
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图 3 蒙古巴音陶勒盖地区二长花岗岩中锆石阴极发光（CL）图像
Figure 3. Zircon CL images of the monzogranite sample in Bayintolgoi, Mongolia
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图 4 蒙古巴音陶勒盖二长花岗岩锆石U-Pb谐和图
Figure 4. U-Pb concordia diagrams of zircons from the monzogranite sample in Bayintolgoi, Mongolia
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图 5 蒙古巴音陶勒盖二长花岗岩锆石年龄直方图
Figure 5. Histograms of zircons from the monzogranite sample in Bayintolgoi, Mongolia
表 1 蒙古巴音陶勒盖二长花岗岩LA-ICP-MS锆石U-Th-Pb同位素分析结果
Table 1 LA-ICP-MS U-Th-Pb isotopic data of zircons from the monzogranite sample in Bayintolgoi, Mongolia
测点 Pb/10-6 U/10-6 Th/U 206Pb/238U 207Pb/235U 207Pb/206Pb 206Pb/238U 207Pb/235U 207Pb/206Pb 比值 1σ 比值 1σ 比值 1σ 年龄/Ma 1σ 年龄/Ma 1σ 年龄/Ma 1σ MND202-1 25 443 1.060 0.04757 0.00035 0.3359 0.0054 0.05122 0.00079 300 2 294 5 251 35 MND202-2 18 306 1.347 0.04776 0.00035 0.3561 0.0082 0.05406 0.00119 301 2 309 7 374 49 MND202-3 14 244 1.436 0.04738 0.00037 0.3396 0.0088 0.05199 0.00133 298 2 297 8 285 58 MND202-4 37 688 1.065 0.04714 0.00031 0.3408 0.0040 0.05244 0.00060 297 2 298 3 304 26 MND202-5 29 529 1.098 0.04572 0.00029 0.3933 0.0074 0.06238 0.00115 288 2 337 6 687 39 MND202-6 17 274 1.800 0.04756 0.00032 0.4313 0.0117 0.06577 0.00176 300 2 364 10 799 56 MND202-7 37 672 1.103 0.04862 0.00031 0.3523 0.0037 0.05255 0.00055 306 2 306 3 310 24 MND202-8 40 791 0.779 0.04613 0.00029 0.3410 0.0047 0.05361 0.00072 291 2 298 4 355 30 MND202-9 18 286 1.678 0.04785 0.00032 0.3664 0.0093 0.05553 0.00138 301 2 317 8 434 55 MND202-10 64 1175 0.962 0.04784 0.00031 0.3683 0.0035 0.05583 0.00051 301 2 318 3 446 20 MND202-11 34 626 0.852 0.04768 0.00031 0.3551 0.0045 0.05403 0.00066 300 2 309 4 372 27 MND202-12 25 469 0.883 0.04760 0.00031 0.3406 0.0053 0.05189 0.00078 300 2 298 5 280 35 MND202-13 39 703 1.084 0.04745 0.00031 0.3688 0.0044 0.05637 0.00064 299 2 319 4 467 25 MND202-14 51 943 1.028 0.04451 0.00028 0.5130 0.0089 0.08358 0.00138 281 2 420 7 1283 32 MND202-15 32 622 0.733 0.04742 0.00032 0.3334 0.0049 0.05100 0.00071 299 2 292 4 241 32 MND202-16 34 672 0.654 0.04749 0.00031 0.3341 0.0044 0.05103 0.00066 299 2 293 4 242 30 MND202-17 39 701 1.120 0.04789 0.00038 0.3488 0.0044 0.05282 0.00062 302 2 304 4 321 27 MND202-18 16 289 1.096 0.04804 0.00036 0.3450 0.0089 0.05209 0.00132 302 2 301 8 289 58 MND202-19 42 947 0.063 0.04786 0.00037 0.3526 0.0038 0.05344 0.00050 301 2 307 3 347 21 MND202-20 37 706 0.845 0.04787 0.00036 0.3432 0.0045 0.05201 0.00060 301 2 300 4 286 27 MND202-21 14 263 0.803 0.04789 0.00039 0.3531 0.0099 0.05347 0.00149 302 2 307 9 349 63 MND202-22 38 643 1.289 0.04802 0.00037 0.3484 0.0045 0.05262 0.00064 302 2 304 4 312 28 MND202-23 19 337 1.105 0.04785 0.00034 0.3645 0.0069 0.05525 0.00104 301 2 316 6 422 42 MND202-24 17 309 0.859 0.04805 0.00035 0.3234 0.0075 0.04881 0.00111 303 2 285 7 139 53 MND202-25 12 202 1.193 0.04693 0.00032 0.3455 0.0116 0.05339 0.00175 296 2 301 10 346 74 MND202-26 41 818 0.879 0.04389 0.00028 0.3536 0.0084 0.05842 0.00137 277 2 307 7 546 51 MND202-27 9 161 1.257 0.04711 0.00033 0.3511 0.0138 0.05406 0.00205 297 2 306 12 373 85 MND202-28 41 811 0.966 0.04422 0.00030 0.3543 0.0056 0.05812 0.00082 279 2 308 5 534 31 MND202-29 24 454 0.936 0.04735 0.00039 0.3476 0.0062 0.05324 0.00086 298 2 303 5 339 37 MND202-30 47 845 1.077 0.04768 0.00034 0.3853 0.0046 0.05862 0.00062 300 2 331 4 553 23 
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