| 内蒙古额济纳地区奥陶纪火山岩地球化学特征及其地质意义 |
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| 引用本文： | 陈智斌,于洋,薄海军.内蒙古额济纳地区奥陶纪火山岩地球化学特征及其地质意义[J].地球科学,2020,45(2):503-518. |
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| 作者姓名： | 陈智斌 于洋 薄海军 |
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| 作者单位： | 1.中国地质大学地质调查研究院, 湖北武汉 430074 |
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| 基金项目： | 中国地质调查局地质调查项目DD2016007802 |
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| 摘 要： | 内蒙古额济纳地区广泛出露的奥陶纪火山岩是中亚造山带南缘中段早古生代地质事件的重要响应，对研究及认识古亚洲洋的演化有着重要的启示.对内蒙古额济纳旗呼仍巴斯克地区咸水湖组火山岩与白云山组凝灰岩进行了岩石学、同位素年代学和全岩主、微量元素地球化学研究.结果显示:咸水湖组为一套基性-酸性熔岩及其同质的火山碎屑岩组合，白云山组凝灰岩为酸性凝灰岩；火山岩与凝灰岩皆属于亚碱性系列岩石，主要表现出钙碱性系列的演化趋势，具有富钙，富铝，贫镁，较大的TFeO/MgO比值的特征，稀土元素配分曲线呈右倾斜型，同时富集大离子亲石元素（LILE）和轻稀土元素（LREE），亏损高场强元素（HFSE）；咸水湖组流纹岩样品的SHRIMP锆石U-Pb同位素谐和年龄为462±3 Ma（MSWD=1.6），显示其形成时代为中奥陶世晚期.通过分析比对认为，不同于其西部希热哈达、伊哈托里等地区的岛弧环境，额济纳旗呼仍巴斯克地区奥陶纪火山岩形成于陆缘弧构造背景，揭示了中-晚奥陶世蒙古国境内Zoolen大洋向内蒙古额济纳地区明水-旱山陆块北缘俯冲作用的存在.
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| 关 键 词： | 火山岩 SHRIMP 年代学 北山弧盆系 额济纳旗 内蒙古 地球化学 |
| 收稿时间： | 2018-11-02 |
Geochemical Characteristics and Geological Significance of the Ordovician Volcanic Rock in Ejiana,Inner Mongolia |
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| Abstract: | As the responses to the geological events on the southern margin of Central Asian Orogenic Belt in early Paleozoic, Ordovician volcanic rocks exposed in Ejin Banner, Inner Mongolia, offer important enlightenment for the evolution of Paleo-Asian Ocean. In this paper, the volcanic rocks and tuffs of Xianshuihu group and Baiyunshan group exposed in Hurengbasike area, Ejin Banner, are studied, including their petrology isotope chronology and geochemical characteristics such as major and trace elements. The results show that the lithology combination of Xianshuihu group is a series of basalt-basaltic andesite-andesite-rhyolite, as well as their volcanic lastic rocks, volcanic debris lava, while tuffs in baiyunshan group are mainly acidic. The volcanic rocks and tuffs belong to the sub-alkaline series, mainly showing the trends of calc-alkaline series evolution, and they are characterized by rich calcium and aluminum, poor magnesium, and larger TFeO/MgO ratios. Besides, the volcanic rocks have enriched LILE, LREE and depleted HFSE, with their REE distribution curves inclining to the right. Test results of SHRIMP zircon U-Pb isotope of the rhyolite sample from xianshuihu group yields a concordia age of 462±3 Ma(MSWD=1.6), indicating its formation era of late Ordovician, The tectonic setting of these volcanic rocks are different from the island arc volcanic rocks of Yihatuoli and Xirehada area in the west, belonging to the active continental margin, revealing the subduction of Zoolen Ocean in Mongolia towards the northern margin of Mingshui-Hanshan block during Middle Ordovician. |
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