| 鄂尔多斯盆地南部延长组长7段凝灰岩形成时代、物质来源及其意义 |
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| 引用本文： | 王建强,刘池洋,李行,吴桐桐,吴经理.鄂尔多斯盆地南部延长组长7段凝灰岩形成时代、物质来源及其意义[J].沉积学报,2017,35(4):691-704. |
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| 作者姓名： | 王建强 刘池洋 李行 吴桐桐 吴经理 |
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| 作者单位： | 1.西北大学地质系, 西安 710069; |
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| 基金项目： | 国家自然科学基金项目，陕西省教育厅基金项目，国家科技重大专项，中国地质调查局项目(12120114009201)National Natural Science Foundation of China |
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| 摘 要： | 鄂尔多斯盆地南部延长组长7段优质烃源岩以含众多凝灰岩夹层为显著特点，其中长7段底部长73层凝灰岩最为发育。凝灰岩的形成时代及火山物质来源，对探讨延长期湖盆优质烃源岩形成、富烃凹陷发育及周邻同期构造-岩浆事件等均具有重要的意义。本文以盆地南部铜川何家坊剖面长73层凝灰岩夹层为重点研究对象，利用岩石薄片、扫描电镜及主微量元素等方法，明确了该区凝灰岩岩石学和地球化学特征；同时对凝灰岩夹层及其间的砂岩层开展了锆石U-Pb定年。结果表明该区凝灰岩蚀变强烈，但仍具凝灰岩结构及中酸性火山岩特点；获得的两个凝灰岩样品主组分加权平均年龄分别是（226.5±1.6）Ma（n=24）和（229.7±2.2）Ma（n=21），同期砂岩碎屑锆石最年轻组分为235~243 Ma（n=7，加权平均年龄239.3 Ma）。结合前人研究成果，综合认为长73层凝灰岩形成年龄约在230 Ma±，代表了长7期开始的时间，也是延长期湖盆进入鼎盛发育和盆地坳陷型富烃凹陷形成的时期。依据延长期凝灰岩特征，盆地腹地及秦岭造山带构造-岩浆活动事件，指出延长组长7期凝灰岩的火山物质主要来自秦岭造山带，与勉略洋壳向南秦岭板块下俯冲形成的岛弧火山等联系密切，并将秦岭造山带与延长期湖盆之间的耦合响应过程划分为3个阶段。本文对重新认识鄂尔多斯盆地发育演化过程及长7期湖盆属性具有重要的指示意义。
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| 关 键 词： | 鄂尔多斯盆地 延长期 凝灰岩 锆石U-Pb定年 秦岭造山带 |
| 收稿时间： | 2016-05-11 |
Geochronology,Potential Source and Regional Implications of Tuff Intervals in Chang-7 Member of Yanchang Formation,South of Ordos Basin |
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| WANG JianQiang,LIU ChiYang,LI Hang,WU TongTong,WU JingLi.Geochronology,Potential Source and Regional Implications of Tuff Intervals in Chang-7 Member of Yanchang Formation,South of Ordos Basin[J].Acta Sedimentologica Sinica,2017,35(4):691-704. |
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| Authors: | WANG JianQiang LIU ChiYang LI Hang WU TongTong WU JingLi |
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| Institution: | 1.Department of Geology, Northwest University, Xi'an 710069, China;2.State Key Laboratory of Continental Dynamics, Northwest University, Xi'an 710069, China |
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| Abstract: | Tuff intervals of Yangchang Formation are widespread in the south of Ordos basin, most of them are well documented at the bottom of Chang 7 segment.The geochronology and volcanic matters of tuff intervals have great significance on the formation of high quality source rock, the development time of hydrocarbon-rich sag and the occurrence of synchronous tectonic-magmatic events.This paper focuses on the tuff intervals, which are located at the bottom of Chang 7 segment in Hejiafang outcrop section, southern Ordos basin.Firstly, thin sections, scanning electron microscopy (SEM) and major and trace elements analysis methods were used to identify the petrographic and geochemical characteristics of the tuff.Then, zircon U-Pb dating method was used to study the geochronology of the tuff intervals as well as the sandstone at the same segment.The results indicate that the tuff has the characteristics of intermediate-acidic volcanic rocks with strong alteration.The weighted average ages of the dominant component in the two tuff samples are 226.5 ± 1.6 Ma (n =24) and 229.7 ± 2.2 Ma (n =21), respectively, while the youngest group ages of detrital zircons range from 235 ~ 243 Ma (n =7, the weighted average age is 239.3 Ma).Combined with previous study results, it is concluded that the age of tuff intervals at the bottom of chang7 segment is around 230 Ma±, which can represent the peak period of Ordos basin's evolution and the beginning development of hydrocarbon-rich sag in Yanchang Formation.According to the characteristics of tuff intervals, the syntectonic events of Ordos Basin and Qinling Orogenic belt over this period, it can be deduced that the volcanic matters of tuff invtervals mainly derived from the Qinling area, related closely to the volcanic arc belt caused by the subduction of Mianlue oceanic crust to the south Qinling plate.The coupling process between the Qinling orogenic belt and the southern Ordos basin can be divided into three periods.The results have important indications to re-recognize the evolution of the Ordos Basin and the basin property at Chang 7 period. |
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| Keywords: | Ordos Basin Yanchang Formation tuff U-Pb zircon dating Qinling orogenic belt |
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