SHRIMP zircon ages of the Dagangou volcanic rocks in the Eastern Kunlun orogenic belt and their implications
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摘要:
东昆仑大干沟以北地区造山后形成的牦牛山组磨拉石建造不整合覆盖于前泥盆系之上,其形成时代对限定柴达木盆地加里东造山作用的结束时间及晚古生代裂解作用的开始时间具有重要意义。应用单颗粒锆石离子探针质谱仪(SHRIMP)方法,对牦牛山组上部火山岩段的样品进行精确的锆石U-Pb测年。结果表明,牦牛山组上段火山岩样品DG01和DG02中的岩浆锆石206Pb/238U平均年龄分别为403.6±5.1Ma和409±3.4Ma。综合前人研究认为,造山后牦牛山组伸展型磨拉石的形成时代为晚志留世-早泥盆世,限定了晚古生代裂解的开始时间,也意味着早古生代加里东造山运动在晚志留世-早泥盆世之前已经结束。
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关键词:
- 东昆仑大干沟 /
- 火山岩 /
- SHRIMP锆石U-Pb年龄 /
- 早泥盆世 /
- 东昆仑造山带
Abstract:The Maoniushan Formation of molasse, formed in a post-orogenic environment in Dagangou area of the Eastern Kunlun Mountains, rests unconformably on pre-Devonian strata. Its formation time is critical for determining the terminal of the Caledonian orogeny and the initiation of splitting in the Late Paleozoic. The authors conducted zircon U-Pb dating for volcanic rocks of the Up-per Maoniushan Formation by SHRIMP. The samples(DG01 and DG02) of the Upper Maoniushan Formation yielded two average zircon U-Pb ages of 403.6±5.1Ma and 409±3.4Ma. Combined with the previous studies, the formation time of the Maoniushan For-mation should be Late Silurian-Early Devonian. This provides a constraint on the starting time of splitting in the Late Paleozoic and also means that the Caledonian orogeny ended before the Late Silurian-Early Devonian.
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图 1 研究区地质略图及采样点位置（据参考文献[①]修改）
QSS—商丹缝合带;Zd—宗务隆构造带;DMS—东昆仑-勉略缝合带
Figure 1. Geological map of the study area showing sampling sites
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图 2 测试样品镜下特征（50倍正交偏光）
a、b—大干沟凝灰岩样品 DG01；c、d—大干沟流纹岩样品DG02。Q—石英； Kfs—钾长石；Pl—斜长石
Figure 2. Microphotographs of samples from volcanic rocks in Dagangou area
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图 3 大干沟火山岩锆石CL图像、测点位置及年龄
Figure 3. CL images of the zircons from the Dagangou volcanic rocks
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图 4 大干沟火山岩样品锆石U-Pb年龄谐和图
Figure 4. Zircon U-Pb concordia diagram of the testing samples from the Dagangou area
表 1 大干沟火山岩SHRIMP锆石U-Th-Pb同位素测定结果
Table 1 SHRIMP U-Th-Pb dating results for zircons from volcanic rocks in Dagangou area
样品 U/10-6 Th/10-6 Th/U 207Pb/206Pb ±% 207Pb/235U ±% 206Pb/238U ±% 206Pb/238U
年龄/Ma207Pb/206Pb
年龄/Ma样品DG01 DG01-1.1 358 181 0.52 0.054 2.7 0.475 3 0.064 1.2 397.3 4.8 378 62 DG01-2.1 577 323 0.58 0.056 1.8 0.486 2.2 0.063 1.2 394.1 4.4 447 40 DG01-3.1 680 421 0.64 0.055 2.5 0.465 2.8 0.061 1.1 384.0 4.2 411 56 DG01-4.1 313 143 0.47 0.054 3 0.457 3.2 0.062 1.3 387.3 4.9 353 67 DG01-5.1 553 288 0.54 0.055 3.6 0.434 3.9 0.058 1.3 361.6 4.5 392 82 DG01-6.1 401 223 0.57 0.057 2.4 0.459 2.7 0.058 1.3 365.4 4.6 496 53 DG01-7.1 518 265 0.53 0.054 2.2 0.426 2.5 0.059 1.2 362.3 4.3 348 51 DG01-8.1 524 270 0.53 0.051 3.2 0.396 3.4 0.059 1.3 356.3 4.4 219 73 DG01-9.1 717 471 0.68 0.055 1.7 0.496 2 0.066 1.1 410.2 4.4 403 37 DG01-10.1 630 445 0.73 0.055 1.8 0.501 2.1 0.066 1.1 410.5 4.4 422 41 DG01-11.1 433 225 0.54 0.054 2.2 0.468 2.5 0.065 1.2 391.2 4.5 382 49 DG01-12.1 697 472 0.7 0.056 2.3 0.529 2.6 0.068 1.1 424.8 4.6 463 51 DG01-13.1 1158 897 0.8 0.059 2.1 0.571 2.4 0.07 1.1 434.7 4.5 582 47 DG01-14.1 406 221 0.56 0.057 2.1 0.503 2.4 0.065 1.2 403.4 4.7 472 46 DG01-15.1 600 324 0.56 0.056 3.3 0.506 3.5 0.065 1.3 408.0 5.1 461 73 DG01-16.1 467 267 0.59 0.057 2 0.502 2.3 0.064 1.2 400.0 4.6 489 43 DG01-17.1 620 352 0.59 0.054 1.6 0.487 1.9 0.065 1.1 405.6 4.4 387 36 DG01-18.1 594 319 0.55 0.055 1.7 0.556 2.1 0.073 1.2 455.4 5.2 414 39 样品DG02 DG02-1.1 553 280 0.52 0.054 3.7 0.493 3.9 0.066 1.2 411.6 4.8 380 83 DG02-2.1 466 243 0.54 0.056 4.3 0.509 4.4 0.066 1.2 411.4 5 452 95 DG02-3.1 489 239 0.5 0.054 3.8 0.491 4.2 0.066 1.7 412.9 6.7 366 86 DG02-3.2 386 230 0.61 0.059 2.7 0.531 3 0.066 1.3 410.5 5 552 59 DG02-4.1 650 395 0.63 0.053 2 0.487 2.3 0.067 1.2 417.4 4.7 322 45 DG02-5.1 528 256 0.5 0.056 2.3 0.497 2.6 0.064 1.2 400.9 4.6 460 52 DG02-6.1 626 339 0.56 0.056 2.8 0.514 3 0.066 1.1 413.8 4.6 462 62 DG02-7.1 665 389 0.61 0.058 3.8 0.557 4 0.069 1.1 431.5 4.7 543 83 DG02-8.1 530 271 0.53 0.056 1.9 0.502 2.2 0.065 1.2 403.4 4.6 468 42 DG02-9.1 488 267 0.56 0.056 2.2 0.491 2.5 0.064 1.2 397.1 4.5 456 49 DG02-10.1 567 294 0.54 0.056 2.5 0.495 2.7 0.065 1.2 404.1 4.5 434 55 DG02-11.1 567 292 0.53 0.058 1.7 0.517 2.1 0.064 1.1 402.4 4.5 536 37 DG02-12.1 634 386 0.63 0.055 2.4 0.511 2.6 0.067 1.2 419.3 4.8 418 53 DG02-13.1 382 180 0.49 0.056 3.3 0.498 3.5 0.065 1.2 403.7 4.8 450 73 DG02-14.1 651 410 0.65 0.053 2.5 0.498 2.8 0.068 1.1 421.6 4.6 347 57 DG02-15.1 647 357 0.57 0.055 1.9 0.491 2.2 0.065 1.1 407.5 4.4 395 43 DG02-16.1 529 279 0.55 0.055 2.2 0.497 2.5 0.066 1.2 411.2 4.6 401 50 
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