刘汉仑, 毛景文, 段士刚, 王梦琦, 王英超, 董泽宝. 浙江治岭头地区玄武岩U-Pb年龄、地球化学特征及构造背景[J]. 地质通报, 2023, 42(5): 753-770. DOI: 10.12097/j.issn.1671-2552.2023.05.008
    引用本文: 刘汉仑, 毛景文, 段士刚, 王梦琦, 王英超, 董泽宝. 浙江治岭头地区玄武岩U-Pb年龄、地球化学特征及构造背景[J]. 地质通报, 2023, 42(5): 753-770. DOI: 10.12097/j.issn.1671-2552.2023.05.008
    LIU Hanlun, MAO Jingwen, DUAN Shigang, WANG Mengqi, WANG Yingchao, DONG Zebao. U-Pb age, geochemistry characteristics and tectonic setting of basalt in the Zhilingtou area, Zhejiang Province[J]. Geological Bulletin of China, 2023, 42(5): 753-770. DOI: 10.12097/j.issn.1671-2552.2023.05.008
    Citation: LIU Hanlun, MAO Jingwen, DUAN Shigang, WANG Mengqi, WANG Yingchao, DONG Zebao. U-Pb age, geochemistry characteristics and tectonic setting of basalt in the Zhilingtou area, Zhejiang Province[J]. Geological Bulletin of China, 2023, 42(5): 753-770. DOI: 10.12097/j.issn.1671-2552.2023.05.008

    浙江治岭头地区玄武岩U-Pb年龄、地球化学特征及构造背景

    U-Pb age, geochemistry characteristics and tectonic setting of basalt in the Zhilingtou area, Zhejiang Province

    • 摘要: 为加深对华南地区东部白垩纪构造演化及壳幔作用的认识,对浙江省治岭头地区发育的玄武岩进行了U-Pb年龄、地球化学和Sr-Nd-Hf同位素分析。玄武岩呈块状构造,斑状结构,斑晶以斜长石、角闪石为主。LA-ICP-MS锆石U-Pb定年结果显示年龄为101±1 Ma,为早白垩世岩浆活动的产物。岩石地球化学分析结果表明,玄武岩整体具有富碱、高K2O/Na2O、高K2O+Na2O值和高Al2O3含量的特征,富集大离子亲石元素(Rb、Sr等)及轻稀土元素,亏损高场强元素(Nb、Ta、Ti、Hf等),稀土元素配分曲线整体右倾,具有微弱的正Eu异常,应属于钾玄岩系列。岩浆演化过程中经历了一定程度的分离结晶作用,Th/La、Th/Ce、Lu/Yb等值更接近于幔源岩浆的比值;(87Sr/86Sr)i=0.70729~0.71029, εNd(t)值及εHf(t)值范围分别为-19.7~-11.8和-9.7~-0.8,指示玄武岩源区具有EMⅠ富集地幔的特征,地壳物质亦有少量参与。结合华南地区晚中生代基性岩浆时空分布及地球化学特征,随着古太平洋板块的持续后撤作用,华南地区早白垩世为弧后扩张环境,由俯冲板片脱水产生的流体交代地幔形成的EMⅠ型富集地幔部分熔融,喷出地表形成了治岭头地区的玄武岩。

       

      Abstract: In order to deepen the understanding of the Cretaceous tectonic setting in the eastern part of South China, the petrological, geochemical and Sr-Nd-Hf isotope analyzes of the basalt in the Zhilingtou area of Zhejiang Province were carried out.The basalt are massive and porphyritic, and the phenocrysts consist of plagioclase and hornblende.LA-ICP-MS zircon U-Pb dating shows that the age is 101±1 Ma, which is the product of Early Cretaceous magmatic activity.The results of geochemical analyzes show that the basalt has the characteristics of rich alkali, high K2O/Na2O ratio, high K2O+Na2O value, and high Al2O3 content, enrichment in large ion lithophile elements(Rb, Sr)and light rare earth elements, depletion in high field strength elements(Nb, Ta, Ti, Hf).The distribution curve of rare earth elements is generally right-sloping, with a weak positive Eu anomaly, which should belong to potash basalt series, and has experienced a certain degree of fractional crystallization during the magma evolution process.The ratios of Th/La, Th/Ce and Lu/Yb are closer to the ratio of mantle-derived magma.(87Sr/86Sr)i=0.70729-0.71029, εNd(t) and εHf(t) values range from -19.7 to -11.8 and -9.7 to -0.8, respectively, indicating that the source area of basalt has the characteristics of EMⅠ-enriched mantle, and a small amount of crustal material is also involved.Structural discriminant diagrams show that basalt was formed in an intraplate extensional environment.In combination with the spatiotemporal distribution and geochemical characteristics of Late Mesozoic basic magma in South China, and with the continuous rollback of the paleo-Pacific plate, South China was a backarc spreading tectonic environment in the Early Cretaceous.The EMⅠ-type enriched mantle formed by fluid metasomatism generated by dehydration of subduction plates partially melted and ejected from the surface to form the basalt in the Zhilingtou area.

       

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