| 摘要: |
| 阿拉善北部雅干地区古生代火山岩发育,研究其形成时代和地质特征,对探讨中亚造山带中段南缘北山弧盆系的演化具有重要的意义。对雅干地区原划奥陶系火山岩进行了同位素年代学与地球化学研究,获得流纹岩LA-ICP-MS锆石U-Pb年龄为298.4±1.5Ma,时代为早二叠世初期,结合岩石组合特征和区域对比,将其重新厘定为上石炭统—下二叠统白山组。该套火山岩富SiO2、高K2O、低TiO2,属于钙碱性系列;相对富集Rb、Pb、K等大离子亲石元素,明显亏损Ta、Nb、P、Ti等高场强元素;呈现为轻稀土元素相对富集、重稀土元素相对亏损的的右倾特征,具有较明显的负Eu异常,显示出陆缘弧火山岩的地球化学特征。上述证据表明,雅干地区白山组火山岩形成于古亚洲洋向明水-旱山地块北缘俯冲的陆缘弧构造环境。 |
| 关键词: 白山组火山岩 锆石U-Pb年龄 地球化学 雅干构造带 阿拉善地区 地质调查工程 |
| DOI：10.12097/j.issn.1671-2552.2023.01.012 |
| 分类号:P597+.3;P597 |
| 基金项目:中国地质调查局项目《内蒙古自治区额济纳旗呼仍巴斯克、查布汗其啥尔乌拉、敦德乌苏、勃温陶来幅1：5万区域地质矿产调查》(编号:DD20208005) |
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| Age and geochemistry of volcanic rocks of Baishan Formation in Yagan tectonic zone,Northern Alxa and their constraints on regional tectonic evolution |
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BAI Yuming1, BO Haijun1, HU Haoyuan1, LEI Congcong1, LI Chengyuan1, YU Yang2
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1.Hohhot Center of Natural Resources Comprehensive Survey, China Geological Survey, Hohhot 010010, Inner Mongolia, China;2.Institute of Geological Survey, China University of Geosciences, Wuhan 430074, Hubei, China
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| Abstract: |
| Paleozoic volcanic rocks are developed in Yagan area,northern Alxa,which is of great significance to study their formation age and geological characteristics for the evolution of the North Mountain arc basin system in the southern margin of the Middle Central Asian orogenic belt.In this paper,the isotope chronology and geochemical characterization of the proto-Ordovician volcanic rocks of the Yagan region are studied.The results show that the LA-ICP-MS zircon U-Pb age of the rhyolite is 298.4±1.5 Ma,which belongs to the early Early Permian.It is redetermined to the Upper Carbonifeous-Lower Permian Baishan Formation based on the characteristics of the lithological assemblage.This set of volcanic rocks belong to the calc-alkaline series,which have higher content of SiO2,higher content of K2O and lower content of TiO2.They are relatively enriched in large ion lithophile elements such as Rb,Pb,K,and are obviously depleted high field strength elements such as Ta,Nb,P and Ti.The sample apparent right-leaning distribution patterns of the REE with depletion in LREE and enrichment in HREE and negative Eu anomaly,and they have the geochemistry characteristics of continental arc.The new evidence shows that Baishan Formation in Yagan area formed in the subduction of Paleo-Asian Ocean towards the northern margin of Mingshui-Hanshan block,and it was resulted from magmatism of the active continental margin. |
| Key words: Baishan Formation volcanic rocks zircon U-Pb age geochemistry Yagan tectonic zone Alxa area geological survey engineering |
