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热带海洋学报

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三叠纪古太平洋俯冲：南海南部陆缘的岩浆记录

王婵1, 刘皓2, 徐维海1   

  1. 1. 热带海洋环境与岛礁生态全国重点实验室(中国科学院南海海洋研究所), 广东 广州 510301;

    2. 中国科学院广州能源研究所, 广东 广州510610

  • 收稿日期:2025-12-25 修回日期:2026-02-09 接受日期:2026-02-12
  • 通讯作者: 刘皓
  • 基金资助:
    国家重点研发计划项目(2021-06); 国家自然科学基金项目(42206073)

Triassic Subduction of the Paleo-Pacific: Magmatic Records from the Southern Continental Margin of the South China Sea

WANG Chan1, LIU Hao2, XU Weihai1   

  1. 1. State Key Laboratory of Tropical Oceanography (South China Sea Institute of Oceanology, Chinese Academy of Sciences), Guangzhou 510301, China;

    2. Chinese Academy of Sciences, Guangzhou 510610, China



  • Received:2025-12-25 Revised:2026-02-09 Accepted:2026-02-12
  • Supported by:

    National Key Research and Development Program Project (2021-06); National Natural Science Foundation of China (42206073)

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摘要： 三叠纪时期南沙地块是华南板块东南缘的重要组成部分, 其蕴含着大量地球动力学及构造转换信息。本文选取该地块内NK-1井作为研究对象, 并结合团队已发表的相关成果，旨在揭示三叠纪时期古太平洋西向俯冲作用的实质。本次最新岩相学和地球化学数据研究显示岩石组合类型分为I、II类玄武岩-玄武安山岩(BA)和英安岩(DA)系列, 喷发形成于晚三叠世早期(217.9±3.5-218.6±3.2Ma), 三个系列均具有典型的弧岩浆体系地球化学特征, 并具有EMII型富集地幔源区属性。古太平洋平板俯冲裹挟的大量陆壳前缘增生楔进入深部并重熔, 产生了大量的熔(流)体加入陆缘一侧软流圈或交代岩石圈地幔熔融形成I类和II类玄武质岩浆房(BA系列); 随着俯冲距离的增加板片前端发生挠曲变形, 诱发了近陆一侧软流圈层上涌，进而导致持续的底侵造成了基性下地壳部分熔融, 形成了DA系列英安质岩浆房。研究区此时幔源岩浆持续上涌导致的岩石圈减薄, 不仅为南沙微地块从华南板块裂离提供条件, 也为后期南海扩张阶段的早期陆内裂谷形成提供契机。

关键词: 古太平洋构造域, 特提斯构造域, 裂谷火山岩, 南沙微地块, 华南板块

Abstract: The Nansha Block (NB) was a significant component of the southeastern margin of the South China Block (SCB) during the Triassic period, which preserves critical records of geodynamic and tectonic transition processes. To reveal the essence of Paleo-Pacific westward subduction during the Triassic, Well NK-1 within this block was selected for petrographic study, and published research data from our team were compared. The latest petrographic and geochemical data reveal that the rock assemblage comprises two distinct types: Type I and Type II basaltic-basaltic andesitic (BA) series and a dacitic (DA) series, which were emplaced during the early Late Triassic (217.9 ± 3.5 to 218.6 ± 3.2 Ma). All three series exhibit typical geochemical signatures of arc magmatism and are derived from an EMII-type enriched mantle source. We propose that the flat-slab subduction of the Paleo-Pacific Plate transported significant volumes of the continental crust frontal accretionary wedge to depth where it underwent remelting. This process generated substantial melts/fluids, which infiltrated the asthenosphere or metasomatized the lithospheric mantle on the side of the continental margin, ultimately triggering mantle melting that formed type I and type II basaltic magma chambers (BA series). With continued subduction, the leading edge of the slab experienced flexural deformation, which induced upwelling of the adjacent asthenosphere on the continental side. This upwelling, in turn, led to persistent underplating, triggering partial melting of the mafic lower crust and generating the DA series dacitic magma chambers. The sustained ascent of mantle-derived magmas during this period resulted in significant lithospheric thinning beneath the study area. This thinning not only facilitated the eventual rifting of the Nansha Micro-block from the South China Block but also preconditioned the region for the subsequent development of early intracontinental rifting during the later seafloor spreading stage of the South China Sea.

Key words: Paleo-Pacific tectonic domain, tectonic evolution, rift volcanic rock, Nansha Block, South China Block