南秦岭早古生代碱性岩地球化学特征及其成因机制:研究进展与展望
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1.大陆动力学国家重点实验室/西北大学地质学系;2.中国科学院海洋研究所,深海研究中心

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国家自然科学基金项目(面上项目,重点项目,重大项目)


Geochemistry and Petrogenesis of Early Paleozoic alkaline rocks in the South Qinling Belts: research progress and prospects
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1.Geological Department,Northwest University;2.Center of Deep Sea Research,Institute of Oceanology,Chinese Academy of Sciences

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    摘要:

    南秦岭地区在早古生代经历了大规模且持续性的碱性岩浆活动,其丰富的碱性岩石记录为探索深部地幔物质组成、壳内岩浆演化过程以及地球动力学演化机制提供了珍贵的地质载体。文章基于团队近期对于区域上典型碱性岩的地球化学分析结果和成因机制探讨,旨在对南秦岭早古生代碱性岩浆的源区和演化过程进行全面地约束。南秦岭早古生代碱性岩石类型主要包括一套成分从碱性玄武质向粗面质变化,呈双峰式分布的碱性火山-侵入岩组合,以及少量与碱性硅酸岩(角闪辉石岩、正长岩)-碳酸岩共生杂岩体。岩相学、年代学和地球化学证据显示这些碱性岩具有相同的地幔源区,其中演化程度较低的镁铁质端元记录了南秦岭早古生代交代岩石圈地幔的部分熔融事件,交代介质主要为硅酸盐熔体。演化程度较高的碱性岩端元(粗面-正长岩、碳酸岩)来源于初始镁铁质组分的岩浆分异过程,其中粗面-正长岩类主要受到以长石和单斜辉石为主的分离结晶作用控制。中生代热液交代过程主要记录在北大巴山东部和武当地块西南缘的早古生代碱性岩体中,热液交代作用促进了碳酸岩杂岩体中稀土元素的富集成矿。副矿物年代学和独居石Nd同位素特征反应了热液可能形成于岩体本身的再活化事件,晚三叠纪秦岭地区的造山运动可能对此过程具有促进作用。

    Abstract:

    The South Qinling belt experienced large-scale and continuous alkaline magmatism during the Early Paleozoic, and the record of alkaline rocks provides a valuable geological vehicle for exploring the deep material composition, magmatic evolution, physicochemical environment and geodynamic evolution of the region. This article aims to provide a comprehensive understanding of the source area and evolution of early Paleozoic alkaline magmatism in the South Qinling Mountains, based on the team's recent work on the genesis of typical alkaline rocks in the region. The Early Palaeozoic alkaline rock types in the South Qinling belt mainly consist of a bimodal suite with a change in composition from basaltic to trachytic, and a small number of carbonatite coeval with alkaline silicate rocks (amphibole pyroxenites and syenite). Petrographic, chronological and geochemical evidence suggests that these alkaline rocks share the same mantle source area, with the mafic rocks recording partial melting of the mantle in the South Qinling Mountains, where the metasomatic agent was mainly silicate melt. The trachyte/syenite and carbonatites are all derived from magmatic differentiation of the initial mafic component, with the trachyte/syenite being controlled by segregation and crystallization of mainly feldspar and clinopyroxene. Hydrothermal processes are mainly concentrated in the Zhuxi-Zhushan area in the eastern part of the Northern Daba Mountains and the south-western margin of the Wudang region, where hydrothermal metasomatism has led to the enrichment of rare earth elements in carbonatite. Geochronology and monazite Nd isotopic signatures suggest that the hydrothermal fluids may have originated from a reactivation event in the rock itself, and that the Late Triassic orogeny of the Qinling region may have contributed to this process.

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  • 收稿日期:2023-05-04
  • 最后修改日期:2023-07-19
  • 录用日期:2023-07-23
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