| 滇东南建水地区高镁火山岩包体的成因和构造背景 |
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| 引用本文： | 刘德民,郭宏杰,张根袁,孔令昊,邵俊琦,张婧琪.滇东南建水地区高镁火山岩包体的成因和构造背景[J].地球科学,2019,44(5):1749-1760. |
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| 作者姓名： | 刘德民 郭宏杰 张根袁 孔令昊 邵俊琦 张婧琪 |
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| 作者单位： | 1.中国地质大学地球科学学院, 湖北武汉 430074 |
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| 基金项目： | 苏北盆地干热岩控热构造背景研究项目2018016417中国地质调查局项目1212011220400 |
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| 摘 要： | 在滇东南建水地区发现产于峨眉山玄武岩中的高镁火山岩包体,这对于地幔柱的形成演化具有重要研究意义.对这些包体进行了锆石U-Pb年代学、地球化学和岩矿分析.高镁火山岩包体具斑状结构,致密块状构造,斑晶主要为贵橄榄石和透辉石.13颗锆石U-Pb LA-ICP-MS加权平均年龄为259±2Ma(MSWD=1.9),显示与寄主岩石同期形成.包体岩石具有高镁(Mg~#=68～75)、低硅(SiO_2=45.11%～45.93%)特征,轻稀土元素(LREE)、高场强元素(HFSE)富集而重稀土元素(HREE)亏损,属于亚碱性、拉斑玄武岩系列,具有板内玄武岩(IPB)特征.火山岩包体的原始岩浆起源于石榴子石二辉橄榄岩低程度部分熔融的产物,岩浆演化过程中发生了橄榄石和单斜辉石的分离结晶作用,在侵位上升过程中未受明显的地壳混染作用.该高镁火山岩的存在,显示地幔柱除了垂直上升运动外,在地球深部不同的边界还有多次侧向扩展移动,表明滇东南晚二叠世存在峨眉山地幔柱的一个分支-地幔枝活动.
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| 关 键 词： | 高镁火山岩包体 峨眉山玄武岩 岩石成因 地幔枝 滇东南建水 构造地质 |
| 收稿时间： | 2019-04-11 |
Petrogenesis and Tectonic Setting of High-Mg Volcanic Rock Xenoliths in Jianshui Area,Southeast Yunnan,China |
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| Affiliation: | (School of Earth Sciences,China University of Geosciences,Wuhan 430074,China;Qinghai Geological Survey Institute,Xining 810012,China;Institute of Geological Survey,China University of Geosciences,Wuhan 430074,China) |
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| Abstract: | It reports for the first time the presence of a suite of high-Mg volcanic xenoliths in Jianshui area of Southeast Yunnan, western Yangtze platform, China, which provides new insights into mantle plume activity in the platform during the Permian. Zircon U-Pb dating, geochemistry and petrology of the xenoliths were studied to assess the petrogenetic origin and geodynamic setting of these high-Mg volcanic rocks in this paper. The high-Mg volcanic xenoliths are porphyritic texture and contain only large phenocrysts of olivine, which show as dense mass, develop as lenticulars in the Permian Emeishan basalts in Jianshui area, Southeast Yunnan. The igneous zircons from the volcanic xenoliths yield a weighted age of ca. 259±2 Ma that is interpreted to be the formation age of the magmatic protolith, which is the same as the host rocks of the Emeishan basalts. The volcanic xenoliths are characterized by low SiO2, moderate TiO2 and high Mg#. All the volcanic xenoliths are enriched in LREE but depleted in HREE. The geochemical characteristics of the xenoliths show that they belong to sub-alkali basalts and intra-plate tholeiitic basalts, suggesting that the primary magma of the high-Mg volcanic rock is likely produced by low partial melting of garnet lherzolite. The original magma may have undergone the process of fractional crystallization of olivines and clinopyroxenes. The original magma has not been affected obviously by crustal material contamination in the emplacement and uplifting. The high-Mg volcanic xenoliths may origin from riched-mantle and may be the product of the main stage of the mantle plume activity. All above indicates that there was a mantle branch developed in the study area in Late Permian. It is proposed that several mantle branches have not only ascending motion but also lateral movement while the thermal melting mantle plume arrives at the boundary of mantle and crust. |
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| Keywords: | high-Mg volcanic xenolith Emeishan basalt petrogenesis mantle branch Jianshui area Southeast Yunnan tectonics |
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