| 西藏洞错地区郎山组晚白垩世火山岩的厘定——新特提斯洋北向俯冲导致增厚下地壳部分熔融的新证据 |
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| 引用本文：次琼,阿旺旦增,索朗顿旦,倪金海,王新录,翟杰.2021.西藏洞错地区郎山组晚白垩世火山岩的厘定——新特提斯洋北向俯冲导致增厚下地壳部分熔融的新证据[J].地球学报,42(1):55-62. |
| DOI：10.3975/cagsb.2020.061502 |
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| 基金项目:中国地质调查局地质调查项目(编号: 121201103000150004) |
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| 中文摘要:郎山组地层是西藏冈底斯带中最具代表性的白垩纪地层, 其时代与形成环境对于认识藏南地区的大地构造演化具有重要意义。基于最近在西藏改则县洞错地区郎山组中新发现的火山岩夹层, 对该火山岩(英安岩)进行了LA-ICP-MS锆石U-Pb定年, 获得年龄值为(88.7±1.1) Ma, 指示该区的郎山组地层应属于上白垩统, 而非之前认为的下白垩统。进一步通过岩石化学分析发现, 该火山岩具有与埃达克岩相似的地球化学特征显示出LREE富集且有轻微的负Eu异常特征, 表明冈底斯带北部地区在晚白垩世早期因新特提斯洋的北向俯冲作用曾发生显著的岩浆活动, 导致增厚下地壳物质部分熔融形成郎山组地层中的火山岩夹层。对郎山组地层时代的重新认定结果以及其中火山岩夹层所反映的深部构造特征, 为研究该区晚白垩世岩浆作用动力学机制提供了新的依据, 也表明需要重新认识藏南地区郎山组地层的区域地质与构造意义。 |
| 中文关键词:西藏改则 晚白垩世火山 新特提斯洋 地壳增厚 板块俯冲 |
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| Identification of Late Cretaceous Volcanic Rocks of Langshan Formation in Dongco Area, Southern Tibet: New Evidence for Partial Melting of a Thickened Lower Crust Triggered by the Northward Subduction of Neo-Tethys |
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| Abstract:The Langshan Formation is the most representative Cretaceous formation in the Gangdise belt of Tibet. LA-ICP-MS zircon U-Pb dating of the volcanic rock (dacite) in the Langshan Formation of Dongco area, Gerze County, Tibet, was conducted based on the newly discovered volcanic intercalation in the Langshan Formation (dacite) in Dongco area, and the obtained age is (88.7±1.1) Ma, indicating that the formation of the Langshan Formation in this area should belong to the Upper Cretaceous rather than the Lower Cretaceous as previously thought. Further rock chemical analysis shows that the volcanic rocks have features similar to those of MrTak rock. Geochemical characteristics exhibit LREE enrichment and slightly negative Eu anomaly, suggesting that the northern Gangdise belt experienced significant magmatic activity in the early Late Cretaceous due to northward subduction of Neo-Tethys, which led to partial melting of thickened crust material to form Langshan Formation volcanic intercalation. The reidentification results of the stratigraphic age of the Langshan Formation and the deep tectonic features reflected by the volcanic intercalation provide a new basis for the study of the dynamic mechanism of Late Cretaceous magmatism in this region, and also indicate that it is necessary to reunderstand the regional geological and tectonic significance of the Langshan Formation in southern Tibet. |
| keywords:Gerze of Tibet Late Cretaceous volcanoes New-Tethys Ocean crustal thickening plate subduction |
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