| 引用本文: | 孙载波,段向东,朱才,周坤,刘和松,赵江泰,浦涛,赵毅,赵枫.三江南段勐海布朗山地区浅变质岩系碎屑锆石U-Pb定年及其构造意义[J].沉积与特提斯地质,2022,42(4):613-625.[点击复制] |
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| 三江南段勐海布朗山地区浅变质岩系碎屑锆石U-Pb定年及其构造意义 |
| 孙载波,段向东,朱才,周坤,刘和松,赵江泰,浦涛,赵毅,赵枫 |
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| (云南省地质调查院, 云南 昆明 650216;自然资源部三江成矿作用及资源勘查利用重点实验室, 云南 昆明 650051;云南省地质调查局, 云南 昆明 650061;云南省地质矿产勘查开发局第一地质大队, 云南 曲靖 655000;云南省核工业地质调查院, 云南 昆明 650106;云南大学地球科学学院, 云南 昆明 650500;内江师范学院地理与资源科学学院, 四川 内江 641100) |
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| 摘要: |
| 布朗山位于西南三江南段勐海地区，大面积出露澜沧岩群。澜沧岩群主要由低级变质作用的砂泥质岩石和少量变中基性火山岩组成，其形成时代、物质来源以及地质意义等一系列问题一直存在很多争议。本文选取该地区澜沧岩群上部层位不含变火山岩地层的浅变质岩开展碎屑锆石阴极发光图像分析和LA-ICP-MS U-Pb年代学研究，明显的环带和较高的Th/U比值表明4件浅变质岩的大部分碎屑锆石是岩浆成因。年代学结果显示，该套地层浅变质岩中的锆石记录了与罗迪尼亚、冈瓦纳超大陆拼合及原、古特提斯洋俯冲有关的岩浆作用信息(1182~1104 Ma、593~560 Ma和378 ~328 Ma)，其最年轻的碎屑锆石年龄(328 Ma)，暗示该套地层形成不早于早石炭世，而非以往认为的新元古代。结合其岩石组合特征，推测该套晚古生代浅变质岩系可能为泥盆-石炭系南段组。在澜沧岩群的年龄频谱特征图中，年轻的550 Ma左右峰期年龄与特提斯喜马拉雅碎屑锆石年龄峰期相同，说明其物源主要为东冈瓦纳北缘的特提斯喜马拉雅构造带，与原特提斯洋和古特提斯洋相关。 |
| 关键词: 澜沧岩群 浅变质岩系 碎屑锆石LA-ICP-MS U-Pb定年 晚古生代 勐海布朗山地区 |
| DOI：10.19826/j.cnki.1009-3850.2022.01008 |
| 附件 |
| 投稿时间：2021-10-06修订日期：2021-12-23 |
| 基金项目:国家自然科学基金项目(92055314、42062005、92055027)、云南省自然资源厅地质勘查基金项目(D2017014)和中国地质调查局项目(DD20160345-02)联合资助 |
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| LA-ICP-MS U-Pb dating of detrital zircon from low-grade metamorphic rocks and its tectonic significances in the Bulangshan area, Menghai Country, Southern Sanjiang Tectonic Zone |
| SUN Zaibo,DUAN Xiangdong,ZHU Cai,ZHOU Kun,LIU Hesong,ZHAO Jiangtai,PU Tao,ZHAO Yi,ZHAO Feng |
| (Yunnan Institute of Geological Survey, Kunming 650216, China;Key Laboratory of Sanjiang Metallogeny and Resources Exploration and Utilization, MNR, Kunming 650051, China;Yunnan Geology Survey, Kunming 650061, China;1st Geological Party, Yunnan Bureau of Geology and Mineral Exploration and Mineral Exploration and Development, Qujing 655000, China;Geological Institute, Geological Bureau of Yunnan Nuclear Industry, Kunming 6500106, China;School of Earth Sciences, Yunnan University, Kunming 650500, Yunnan, China;School of Geography and Resource Science, Neijiang Normal University, Neijiang 641100, China) |
| Abstract: |
| Bulangshan is located in the Menghai area, southern Sanjiang area of southwestern China, where Lancang Group is exposed. Lancang Group is mainly composed of sandy and muddy rocks with low-grade metamorphism and a small amount of intermediate and basic volcanic rocks. A series of issues about the Lancang Group such as the formation age, material sources and geological significance of the strata have been disputed for a long time. Detrital zircons from the low-grade metamorphic rocks without metavolcanic strata in the upper layer of the Lancang Group were carried out cathodoluminescence image analysis and LA-ICP-MS U-Pb chronology analysis. Clear oscillatory zoning and higher Th/U ratios indicate that most detrital zircons are magmatic origin. The chronological results show that the magmatism events recorded by the zircons were related to the supercontinent assembly of Rodinia and Gondwana and the subduction of the Proto- and Palaeo-Tethyan ocean (1182-1104 Ma, 593-560 Ma and 378-328 Ma), the youngest detrital zircon ages (328 Ma) suggesting that the strata didn’t form before the Early Carboniferous, rather than the Neoproterozoic. Combined with the rock assemblage characteristics, it is speculated that the Late Paleozoic low-grade metamorphic rocks may be the Carboniferous Nanduan Formation. In the detrital zircon age spectrum of the Lancang Group, the young peak age is ~550 Ma, which is similar to the Tethys Himalayas. So the materials sources of the Lancang Group maybe mainly come from the northerm margin of Eastern Gondwana, and have relationship with the Proto- and Paleo- Tethys oceans. |
| Key words: Lancang Group low-grade metamorphic rocks detrital zircon LA-ICP-MS U-Pb data Late Paleozoic Bulangshan, Menghai area |
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