| 河北秦皇岛石门寨中生代火山岩的地球化学特征和锆石LA-ICP-MS U-Pb年龄 |
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| 引用本文： | 赵瑞鹏,陈亮,刘道宏,杨潇潇.河北秦皇岛石门寨中生代火山岩的地球化学特征和锆石LA-ICP-MS U-Pb年龄[J].地质论评,2019,65(4):929-947. |
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| 作者姓名： | 赵瑞鹏 陈亮 刘道宏 杨潇潇 |
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| 作者单位： | 西北大学地质学系,大陆动力学国家重点实验室,西安,710069;中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广州,510640;中国科学院大学,北京,100049;西北大学地质学系,大陆动力学国家重点实验室,西安,710069 |
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| 基金项目： | 本文为国家级大学生创新训练计划项目（编号：201510697035）和国家基础科学人才培养基金（编号：XDCX2015- 01）的成果。 |
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| 摘 要： | 中国东部中生代火山岩比较发育，在冀北—辽西、山东、北淮阳、太行山等地区均有分布。在冀北的秦皇岛石门寨地区存在着一套分布广泛的中生代蓝旗组与孙家梁组火山岩，不整合在侏罗系北票组砾岩之上。蓝旗组与孙家梁组之间为整合关系，蓝旗组主体为碱玄岩和玄武粗安岩，孙家梁组主体为英安岩和流纹岩，前人研究认为其时代为晚侏罗世。本研究对该地区火山岩样品进行了全岩地球化学分析和锆石U- Pb定年。蓝旗组火山岩样品总体上以富K、Na和Al为特征，部分样品有较高的Mg和Fe含量，在微量元素组成上，粗面岩和玄武粗安岩富集大离子亲石元素和轻稀土元素，亏损高场强元素和重稀土元素，碱玄岩轻微亏损高场强元素，轻重稀土元素分馏较为明显，玄武岩无明显高场强元素异常，轻稀土无明显富集，重稀土不亏损。孙家梁组火山岩样品均为流纹岩，也以富K、Na和Al为特征，Mg和Fe含量较低，在微量元素组成上，富集轻稀土元素，亏损重稀土元素，具有强烈的Eu负异常。蓝旗组火山岩主要为钾玄岩系列，孙家梁组火山岩为高钾钙碱性系列，蓝旗组粗面岩和玄武粗安岩地球化学特征类似岛弧，可能与受上地壳俯冲脱水交代作用有关，碱玄岩地球化学特征类似HIMU型OIB，源区可能为受俯冲洋壳交代所形成的富集型软流圈地幔，玄武岩地球化学特征类似N- MORB，源区可能为亏损的软流圈地幔。孙家梁组流纹岩可能由早白垩世华北克拉通强烈的伸展作用导致幔源岩浆底侵下地壳，使其部分熔融或古太平洋板块俯冲后撤所导致俯冲洋壳岩石发生部分熔融产生。孙家梁组流纹岩中锆石的LA- ICP- MS U- Pb定年获得了23个颗粒的加权平均年龄1180±11 Ma，为早白垩世，可以与辽西地区义县组相对比。河北秦皇岛石门寨地区蓝旗组和孙家梁组火山岩的成因及形成时代对于探讨中生代华北克拉通减薄的机制与时限具有重要意义。
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| 关 键 词： | 蓝旗组 孙家梁组 中生代火山岩 中国东部 锆石U-Pb年龄 |
| 收稿时间： | 2018/7/21 0:00:00 |
| 修稿时间： | 2019/6/27 0:00:00 |
Geochemical features and zircon LA- ICP- MS U- Pb ages of Mesozoic volcanic rocks in Shimenzhai, Qinhuangdao, Hebei Province |
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| ZHAO Ruipeng,CHEN Liang,LIU Daohong and YANG Xiaoxiao.Geochemical features and zircon LA- ICP- MS U- Pb ages of Mesozoic volcanic rocks in Shimenzhai, Qinhuangdao, Hebei Province[J].Geological Review,2019,65(4):929-947. |
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| Authors: | ZHAO Ruipeng CHEN Liang LIU Daohong and YANG Xiaoxiao |
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| Abstract: | Objectives: Mesozoic volcanic rocks are widespread in eastern China. In Shimenzhai, Qinhuangdao, northern Hebei province, there occur a suite of Mesozoic volcanic rocks of the Lanqi Formation and the Sunjialiang Formation, unconformitly overlying on the Jurassic conglomerate of the Beipiao Formation. The Lanqi Formation consists of tephrites, trachyandesites and tephrites, and the Sunjialiang Formation mainly consists of dacites and rhyolites. The petrogenesis and age of volcanic rocks of the Lanqi Formation and the Sunjialiang Formation in Shimenzhai, Qinhuangdao, Hebei province is important for discussing mechanism and timing of thinning of North China Craton in Mesozoic.
Methods: Whole rock geochemistry analysis and zircon U- Pb age dating are carried out on selective volcanic rocks samples of the Lanqi Formation and the Sunjialiang Formation.
Results: The volcanic rocks of the Lanqi Formation are mafic alkaline, with high K, Na and Al contents, some of samples also have high Mg and Fe contents. Trachytes and trachyandesites are enriched in LILE and LREE, depleted in HFSE and HREE. Tephrites are slightly depleted in HFSE, with significant fractionation between LREE and HREE. Basalts have no HFSE anomaly, LREE enrichment and HREE depletion. The volcanic rocks of the Sunjialiang Formation have high K, Na, Al, and low Mg and Fe contents. They have LREE enriched patterns, with significant negative Eu anomalies. The Lanqi Formation is mainly shoshonite series, and the Sunjialiang Formation is high K calc alkaline series.
Conclusions: The geochemical characteristics of trachyte and basaltic trachy- andesite of the Lanqi Formation are similar to those of island arc, which may be related to the subduction and dehydration metasomatism of the upper crust. The geochemical characteristics of tephrite are similar to those of HIMU type OIB, and the source region may be enriched asthenospheric mantle by metasomatism of the subducted oceanic crust. The geochemical characteristics of basalt are similar to those of N- MORB, and the source area may be depleted asthenospheric mantle. The rhyolites of the Sunjialiang Formation may be partial melting of lower crust by underplating of mantle source magma by the Early Cretaceous extension of North China Craton or the partial melting of subducted oceanic crustal rocks by subduction of the palaeo- Pacific plate. LA- ICP- MS U- Pb dating on zircons from a rhyolite of the Sunjialiang Formation, yield a concordant age of 118.0±1.1Ma. This age indicate that the Sunjialiang Formation is chronologically comparable with Yixian Formation in western Liaoning province. |
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| Keywords: | Lanqi Formation Sunjialiang Formation Mesozoic volcanic rocks Eastern China zircon U- Pb age |
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