缪宇, 韦少港, 吕晓春, 宋文婷, 万理文. 滇东北中元古界下昆阳群鹅头厂组变质岩地球化学特征及其形成环境[J]. 地质通报, 2020, 39(10): 1538-1548.
    引用本文: 缪宇, 韦少港, 吕晓春, 宋文婷, 万理文. 滇东北中元古界下昆阳群鹅头厂组变质岩地球化学特征及其形成环境[J]. 地质通报, 2020, 39(10): 1538-1548.
    MIAO Yu, WEI Shaogang, Lü Xiaochun, SONG Wenting, WAN Liwen. Geochemical characteristics and formation environment of metamorphic rocks in Etouchang Formation of Middle Proterozoic Lower Kunyang Group in northeastern Yunnan[J]. Geological Bulletin of China, 2020, 39(10): 1538-1548.
    Citation: MIAO Yu, WEI Shaogang, Lü Xiaochun, SONG Wenting, WAN Liwen. Geochemical characteristics and formation environment of metamorphic rocks in Etouchang Formation of Middle Proterozoic Lower Kunyang Group in northeastern Yunnan[J]. Geological Bulletin of China, 2020, 39(10): 1538-1548.

    滇东北中元古界下昆阳群鹅头厂组变质岩地球化学特征及其形成环境

    Geochemical characteristics and formation environment of metamorphic rocks in Etouchang Formation of Middle Proterozoic Lower Kunyang Group in northeastern Yunnan

    • 摘要: 昆阳群浅变质岩系作为扬子陆块西缘变质褶皱基底的重要组成部分,其形成及演化机制一直备受关注。以昆阳群代表性地层鹅头厂组变质岩为例,从岩石共生组合、岩相学标志、岩石地球化学等方面对该套变质岩原岩类型、物源、沉积及构造环境背景进行约束。变质岩微古生物及同位素年龄显示,该套变质岩成岩时代属中元古代晚期,沉积相及岩相学表现为正常海相沉积原岩特征。岩石地球化学分析显示,变质岩原岩为杂砂岩及亚杂砂岩类,兼有部分泥岩成分,形成于浅海-滨海相的氧化沉积环境。岩石整体经历过中等程度的风化淋滤作用,成熟度较低。沉积物质主要来源于上地壳构造活动区,具有活动构造带单次循环沉积产物的特征,并经历过一定程度的壳内地化分异作用。沉积物源以大陆岛弧型低铝TTG系列火山岩为主,兼有部分上地壳陆源物质的介入。岩石地球化学特征还指示,该套变质岩原岩主要沉积于被动大陆边缘的构造环境,很可能形成于昆阳海洋裂谷盆地闭合阶段后期的残留海盆。

       

      Abstract: As an important part of the metamorphic fold basement on the western margin of the Yangtze block, the light metamorphic rock series of Kunyang Group has attracted much attention from experts for its formation and evolution mechanism.Taking the metamorphic rocks of Etouchang Formation, the representative stratum of Kunyang Group, as an example, this paper constrains the protolith type, provenance, sedimentation and tectonic environment background of the metamorphic rocks in the aspects of rock symbiotic association, petrographic markers and petrogeochemical.The micropaleontology and isotopic age of the metamorphic rocks indicate that the diagenetic age of the metamorphic rocks belongs to Late Mesoproterozoic, and the sedimentary facies and petrographic shows the characteristics of normal marine sedimentary.Comprehensive petrogeochemical analysis shows that the original rocks of metamorphic rocks were composed of graywacke and subgraywacke with some mudstone components, which were formed in the oxidative sedimentary environment of the shallow-littoral facies.The rocks experienced moderate weathering and leaching with lower rock maturity and leaching with lower rock maturity.The sediments mainly came from the tectonic active area of the upper crust, with the characteristics of single cycle sedimentary products in the active structural belt and experienced a certain degree of intracrustal geochemical differentiation.The main source of the sediments was the continental island arc type low aluminum TTG series volcanic rocks, with the intervention of part of the upper crust terrigenous materials.Furthermore, petrogeochemical characteristics also show that the metamorphic protolith mainly deposited in the passive continental margin tectonic environment.The authors hold that the metamorphic protoliths were probably formed in the residual basin in the late closure stage of Kunyang marine rift basin.

       

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