张宏辉, 李致伟, 陈贵仁, 吴亮, 张沥元. 0: 乌蒙山地区茅口组中上部火山物质的发现及地质意义:峨眉地幔柱早期活动的证据. 地质通报. DOI: 10.12097/gbc.2023.07.002
    引用本文: 张宏辉, 李致伟, 陈贵仁, 吴亮, 张沥元. 0: 乌蒙山地区茅口组中上部火山物质的发现及地质意义:峨眉地幔柱早期活动的证据. 地质通报. DOI: 10.12097/gbc.2023.07.002
    Honghui ZHANG, Zhiwei LI, Guiren CHEN, Liang WU, Liyuan ZHANG. 0: Discovery of Volcanic Matter in the Upper Maokou Formation in Wumengshan Area and Its Geological Significance:Evidence of Early Activity of the Emeishan Mantle Plume. Geological Bulletin of China. DOI: 10.12097/gbc.2023.07.002
    Citation: Honghui ZHANG, Zhiwei LI, Guiren CHEN, Liang WU, Liyuan ZHANG. 0: Discovery of Volcanic Matter in the Upper Maokou Formation in Wumengshan Area and Its Geological Significance:Evidence of Early Activity of the Emeishan Mantle Plume. Geological Bulletin of China. DOI: 10.12097/gbc.2023.07.002

    乌蒙山地区茅口组中上部火山物质的发现及地质意义:峨眉地幔柱早期活动的证据

    Discovery of Volcanic Matter in the Upper Maokou Formation in Wumengshan Area and Its Geological Significance:Evidence of Early Activity of the Emeishan Mantle Plume

    • 摘要: 为了加深对滇东北乌蒙山地区峨眉地幔柱活动演化的认识,对该区的的茅口组中上部凝灰质灰岩的同位素年代学、锆石微量元素、锆石Hf同位素及牙形刺生物地层等进行了研究,研究表明:茅口组中上部最底层凝灰岩的锆石U-Pb年龄为268.7±1.7Ma,发现的牙形刺为Jinogondolella aserrata,是二叠系瓜德鲁普统沃德阶的典型分子,与锆石U-Pb年龄对应。锆石微量元素特征显示其与峨眉山玄武岩一致,为基性岩浆锆石,且其与峨眉山玄武岩凝灰岩均为大陆弧型构造背景,证明其与峨眉山玄武岩同源,可能代表峨眉山大火成岩省大规模喷发之前的火山活动,6个锆石Hf同微素特征显示εHf(t)均值为-5.7,显示峨眉地幔柱早期的火山活动受到地壳的混染较大。茅口组凝灰质灰岩的发现表明峨眉地幔柱在乌蒙山地区于阳新世沃德期已经发生小规模的岩浆喷发活动,为峨眉地幔柱模型的建立增加新的证据。

       

      Abstract: To deepen our understanding on the evolution of the Emeishan mantle column activity in the Wumengshan area of northeastern Yunnan, the isotopic chronology, zircon trace element, zircon Hf isotopes and dental spines of the middle and upper tuffs of the Maokou Formation in this area were investigated, the result shows that the zircon U-Pb age of the uppermost tuffs of the Maokou Formation is 268.7 ± 1.7 Ma, and the conodont found is Jinogondolella aserrata, which is a typical molecule of the Permian Guadalupian Wordian, corresponds to the zircon U-Pb age. The zircon trace element characteristics show that it is consistent with the Emeishan basalt and is a basal magmatic zircon, and it is in a continental arc-type tectonic setting with both the Emeishan flood basaltic tuffs, proving that it is homologous with the Emeishan flood basalt and may represent the volcanic activity before the large-scale eruption of the Emeishan Large Igneous Province. The average εHf(t) of the 6 zircons is -5.7, indicating that the early volcanic activity of the Emeishan mantle plume was strongly influenced by the crust. The discovery of tuffaceous limestone in Maokou Formation indicates that the Emeishan mantle plume occurred in Wumengshan area in the Permian Guadalupian Wordian, which adds new evidence for the establishment of the Emeishan mantle plume model. .

       

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