鲁西地区新生代周村玄武岩的成因研究

发布时间：2018-10-11 12:17

【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。
[Abstract]:The Cenozoic basalts in Shandong are mainly distributed in the Tanlu fault zone and its east area, but less in the western part of Shandong province. In this paper, the main rock, trace elements, olivine porphyry and Pb isotopic composition of melt inclusions of Zhoucun basalt in western Shandong are reported. The results show that Zhoucun basalt is a weakly alkaline basalt, and its main elements are characterized by higher SiO_2, lower Na_2O K 2O and CaO/Al_2O_3,Fe_2O_3~T (Fe_2O_3~T=Fe O / 0.8998 Fe_2O_3), and trace elements are similar to EMI oceanic basalt (OIB) on the primitive mantle normalized cobweb map. There were significant positive Ba,K and Sr anomalies, negative Th and Pb anomalies, no Nb,Ta and Ti anomalies, and melt inclusions with ~ (207) Pb/~ (206) Pb and ~ (208) Pb/~ (206) Pb were 0.8940.92 and 2.166 ~ 2.213, respectively, slightly higher than EMI-OIB.. These characteristics are distinct from those of Wudi Dashan basalt in western Shandong, but are similar to those of weakly alkaline tholeiite in other areas of Shandong Province. The porphyry Ni,Fe/Mn and Ca of olivine in Zhoucun basalt are 1403 ~ 2611 渭 g / g and 824 渭 g / g respectively. Compared with olivine composition crystallized in peridotite melt, the porphyry crystal of Zhoucun basalt olivine has the characteristics of high Ni and Fe/Mn ratios and low Ca, given the Fo value of olivine. Combined with the low CaO and high FeO/MnO ratios of the whole rock, olivine composition indicates that the lithology of the source area of the basalt in Zhoucun is pyroxenite, and its formation requires a high proportion of peridotite derived from the recirculating crust in the metasomatism of the mantle. The characteristics of trace elements in the high proportion of melts and basalts in Zhoucun further indicate that the crust of the recycling is an oceanic crust containing gabbro. The results of this paper suggest that the source area of weakly alkaline tholeiite in Shandong area is mainly related to the recirculating oceanic crust.
【作者单位】：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;中国科学院大学;中国科学院南海海洋研究所;
【基金】：国家自然科学基金重大研究计划(91214202)资助
【分类号】：P588.145

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