| 羌塘地块南部晚白垩世火山岩离子探针测年及其对红层时代的约束 |
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| 引用本文：吴珍汉,吴学文,赵珍,陆露,叶培盛,张耀玲.2014.羌塘地块南部晚白垩世火山岩离子探针测年及其对红层时代的约束[J].地球学报,35(5):567-572. |
| DOI：10.3975/cagsb.2014.05.06 |
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| 基金项目:青藏高原地质矿产调查评价专项“羌塘盆地油气地质构造保存条件研究”(编号: 1212011221111) |
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| 中文摘要:羌塘地块南部广泛出露陆相红层, 1:25万区域地质调查将大部分红层划归为中新统康托组, 但缺乏可靠的年代学依据。野外观测发现火山岩与红层之间存在喷发不整合接触关系, 室内从火山岩选出很多岩浆锆石; 应用离子探针U-Pb同位素测年方法精确测定岩浆锆石年龄, 能够为研究火山喷发期次和红层形成时代提供重要依据。对羌塘地块南部红层内部粗面安山岩夹层—比洛错火山岩和扎加藏布北侧红层上覆安山岩, 挑选岩浆锆石进行高精度的离子探针U-Pb同位素测年, 发现比洛错粗面安山岩锆石206Pb/238U同位素年龄为(83.3?1.3) Ma, 扎加藏布北侧安山岩锆石206Pb/238U同位素年龄为(75.65?0.82) Ma。这些年龄良好地揭示了晚白垩世不同期次的火山喷发时代, 同时为红层形成时代和红层盆地演化提供了重要的年代学约束。根据比洛错和扎加藏布北侧火山岩的锆石U-Pb同位素测年资料, 将羌塘盆地南部红层时代归属上白垩统阿布山组, 这对分析羌塘地块南部油气地质构造保存条件和构造地貌演化具有重要意义。 |
| 中文关键词:陆相红层 火山岩 晚白垩世 离子探针U-Pb同位素测年 羌塘地块南部 |
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| SHRIMP U-Pb Isotopic Dating of the Late Cretaceous Volcanic Rocks and Its Chronological Constraint on the Red-beds in Southern Qiangtang Block |
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| Abstract:Although no qualified chronological data are available for the red-beds, stratigraphic systems of redbeds outcropped widely in southern Qiangtang Block have been mostly regarded as belonging to the Miocene Kangtuo Formation according to regional geological survey at a scale 1:250,000. In this study, the red beds intercalated with volcanic rocks were discovered in the field, and magmatic zircons were selected from the volcanic rocks, which were suitable for the SHRIMP U-Pb isotopic dating so as to provide isotopic ages of high resolution for volcanic eruptions and further to give constraint on geological time of the related red-beds. The SHRIMP 206Pb/238U isotopic ages of magmatic zircons are (83.3?1.3) Ma and (75.65?0.82) Ma respectively for the trachyte-andesite intercalations in red beds of northern Belog Co and the andesite overlying red-beds in northern Zagya Zangbu. These high-resolution isotopic ages not only well reveal periods of volcanic eruptions in Late Cretaceous but also provide chronological evidence for the Late Cretaceous basins of red-beds in southern Qiangtang Block. Geological time of the terrestrial red-beds outcropped widely in southern Qiangtang basin should be changed from the Miocene Kangtuo Formation to the Upper Cretaceous Abushan Formation according to the SHRIMP U-Pb isotopic dating of volcanic rocks in northern Belog Co and Zagya Zangbu. Such change is significant for the better understanding of tectonic evolution and geological preservation conditions of oil-gas systems in southern Qiangtang Block. |
| keywords:terrestrial red-beds volcanic rocks Late Cretaceous SHRIMP U-Pb isotopic dating southern Qiangtang Block |
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