| 鲁西地区新生代周村玄武岩的成因研究 |
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| 引用本文： | 张银慧,任钟元,洪路兵,张乐,钱生平,吴亚东,丁相礼,徐义刚,陈林丽.鲁西地区新生代周村玄武岩的成因研究[J].大地构造与成矿学,2017,41(1). |
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| 作者姓名： | 张银慧 任钟元 洪路兵 张乐 钱生平 吴亚东 丁相礼 徐义刚 陈林丽 |
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| 作者单位： | 1. 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,广东广州510640;中国科学院大学,北京100049;2. 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,广东广州510640;3. 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,广东广州510640;中国科学院 南海海洋研究所,广东广州510301 |
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| 基金项目： | 国家自然科学基金重大研究计划 |
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| 摘 要： | 山东地区新生代玄武岩主要分布在郯庐断裂带及其以东地区,在鲁西地区分布较少。本文报道了鲁西地区周村玄武岩的全岩主、微量元素组成、橄榄石斑晶及其熔体包裹体Pb同位素组成。结果表明,周村玄武岩为弱碱性玄武岩,其主量元素具有较高SiO_2和Al_2O_3,较低碱(Na_2O+K_2O)、CaO/Al_2O_3、Fe_2O_3~T(Fe_2O_3~T=Fe O/0.8998+Fe_2O_3)的特征;微量元素在原始地幔标准化蛛网图上与EMI洋岛玄武岩(OIB)相似,表现为明显的Ba、K和Sr正异常,Th和Pb负异常,无Nb、Ta和Ti异常;熔体包裹体~(207)Pb/~(206)Pb和~(208)Pb/~(206)Pb分别为0.894~0.921和2.166~2.213,略高于EMI-OIB。这些特征和鲁西地区无棣大山玄武岩有明显区别,但与山东其它地区的弱碱性-拉斑玄武岩相似。周村玄武岩的橄榄石斑晶Ni、Fe/Mn和Ca分别为1403~2611μg/g,70~93和824~2003μg/g。与橄榄岩熔体结晶的橄榄石成分相比,给定橄榄石Fo值,周村玄武岩橄榄石斑晶具有高Ni和Fe/Mn比值,低Ca的特征。结合全岩低CaO和高FeO/MnO比值,橄榄石成分指示周村玄武岩的源区岩性为辉石岩,其形成需要高比例的来自再循环地壳的英安质熔体交代地幔橄榄岩。高比例的英安质熔体和周村玄武岩的微量元素特征,进一步说明该再循环地壳为含辉长岩洋壳。本文的研究结果暗示山东地区弱碱性-拉斑玄武岩的源区辉石岩,主要与再循环洋壳有关。
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| 关 键 词： | 华北克拉通 新生代玄武岩 辉石岩 熔体包裹体 橄榄石 |
Petrogenesis of Cenozoic Zhoucun Basalts,Western Shandong |
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| Abstract: | Cenozoic basalts in Shandong province are mainly distributed along and east to Tanlu Fault Zone,with minor in West Shandong.This study reported major and trace element compositions of bulk rocks,in situ Pb isotope compositions of melt inclusions and their host olivine chemistry in Zhoucun basalts,Western Shandong to constrain their petrogenesis.The results show that the Zhoucun basalts are weakly alkali basalts,with high SiO2 and A12O3,low total alkali contents,CaO/A12O3 and Fe2O3T in major elements.Their trace element compositions have EMI-oceanic island basalts' flavor,with LILE enrichment,significant positive anomalies of Ba,K and Sr,negative anomalies of Thand Pb,and no anomalies of Nb-Ta and Ti.Pb isotope compositions of the melt inclusions hosted in the melt inclusions ranges from 0.894-0.921 for 207pb/206pb and 2.166-2.213 for 208pb/206pb,overlapping but generally a little higher than EMI-oceanic island basalts'.These features are distinctively different from those of the Dashan basalts in Wudi,Western Shandong,but comparable to those of the weakly alkali-tholeiitic basalts in the other locations in Shandong province.Olivine phenocrysts in Zhoucun basalts have Ni 1403-2611 μg/g,Fe/Mn ratios 70-93,Ca 824-2003 μg/g.Comparing with the peridotitic melts-derived olivine phenocrysts,they generally have higher Ni and Fe/Mn,lower Ca at given Fo values.Together with low CaO and high FeO/MnO of their bulk rocks,the olivine chemistry in Zhoucun basalts argue for pyroxenite as the source lithology,which were formed via high proportion of recycled crust-derived dacitic melts reacting with the surrounding peridotite.Such high proportion of dacitic melts,together with the trace element compositions,further indicates that the recycled crust is gabrro-bearing oceanic crust.The outcomes of this study suggest that the ubiquitous pyroxenite in the source of the weakly-theloiitic basalts in Shandong province is likely associated with the recycled oceanic crust. |
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| Keywords: | North China Craton Cenozoic basalts pyroxenite melt inclusion olivine |
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