旌德岩体花岗闪长岩与MME的同源性及其地质意义——来自黑云母的地球化学证据
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本文为国家自然科学基金资助项目(编号:41602051),安徽省自然资源科技项目(编号:2020- K- 12),安徽省公益性地质工作项目(编号:2024- g- 1- 7)和中央高校基本科研业务费专项资金资助项目(编号:JZ2021HGTB0108)的成果


Homology of granodiorite and MME in the Jingde pluton and its geologic significance——Geochemical evidence from biotite
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    摘要:

    暗色微粒包体(mafic microgranular enclave, MME)广泛存在于花岗质岩石中,其成因对于理解岩浆深部演化过程具有重要意义。燕山期旌德岩体位于江南造山段东段,内部广泛发育暗色微粒包体。本文对旌德岩体中MME开展详细的岩相学,重点选择花岗闪长岩和MME中黑云母进行矿物化学分析,并结合前人已有的工作,通过建立花岗闪长岩与MME之间的成因联系,限定MME成因。花岗闪长岩和MME中黑云母演化程度均较低,二者具有相似的形成温度分别为(824~864 ℃、802~828 ℃)、压力(0.354~0.787 GPa、0.279~0.358 GPa)和氧逸度(-13.4~-12.7、-12.8~-11.2)。花岗闪长岩和MME在物理化学条件和地球化学成分上呈现出高度的一致性,反映二者很可能来源于同源母岩浆。在古太平洋板块俯冲背景下,具有富集特征的扬子岩石圈地幔部分熔融形成玄武质岩浆并在下地壳发生分异作用,岩浆房内早期低演化岩浆由于较低黏度先上侵冷却,后高演化的花岗闪长质岩浆大规模上侵,并将岩浆通道中早期半塑性的中基性岩石拖拽裹挟至浅部地壳,形成旌德岩体及包裹的MME。

    Abstract:

    In order to study the possible formation mechanism of MME in the Jingde pluton. Mineral chemical analyses of granodiorite and biotite in the MME were conducted to qualify the magma crystallization conditions and establish the diagenetic link between the MME and host granodiorite.Methods: Combined with field work and microscope observation, using EPMA and LA- ICP- MS analysis of biotite and plagioclase to constrain the origin of MME.Results and conclusion:(1) In the Jingde pluton granodiorite and MME formed at analogous temperatures (824~864 ℃, 802~828 ℃), pressures (0.354~0.787 GPa, 0.279~0.353 GPa) and oxygen fugacity (-13.4~-12.7, -12.8~-11.2), respectively.(2)The compositions of biotite and plagioclase in the Jingde pluton MME are comparable to that of the host granodiorite, indicating that MME is not of crust—mantle mixing origin, but a cognate magmatic evolutionary relationships.(3)The enriched mantle was partially melted induced by the subduction of the Paleo- Pacific plate and formed basaltic magma. The underplated basaltic magma evolved to intermediate melt by differentiation. Early low-evolving magma is the magma chamber cooled first by upward introsions due to lower viscosity, followed by a large-scale upward intrusion of highly evolved granodiorite magma. The cooled semi- plasticized intermediate rocks in the magma channel were dragged and wrapped to form MMEs in the granodiorite.

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闫候贝,王志强,孙克克,袁峰,陶耐,张军.2024.旌德岩体花岗闪长岩与MME的同源性及其地质意义——来自黑云母的地球化学证据[J].地质论评,70(3):2024030007,[DOI].
YAN Houbei, WANG Zhiqiang, SUN Keke, YUAN Feng, TAO Nai, ZHANG Jun.2024. Homology of granodiorite and MME in the Jingde pluton and its geologic significance——Geochemical evidence from biotite[J]. Geological Review,70(3):2024030007.

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  • 收稿日期:2023-12-05
  • 最后修改日期:2024-04-29
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  • 在线发布日期: 2024-05-19
  • 出版日期: 2023-05-15