东昆仑三叠纪两期长英质火山活动的时代与动力学背景——来自锆石U-Pb年代学和地球化学的约束
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P571;P595

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国家自然科学基金项目(41602049); 四川省自然科学基金项目(2024NSFSC1991); 自然资源部黄河上游战略性矿产资源重点实验室科研项目(YSJD2022-14); 中国地质调查局项目(DD20240074-02)


Ages and tectonic settings of two episodic Triassic felsic volcanism in the East Kunlun: Constraints from zircon U-Pb geochronology and geochemistry
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    摘要:

    东昆仑造山带三叠纪火山岩蕴藏着丰富的岩浆-构造动力学信息,是探究古特提斯造山作用过程的重要探针。本文以东昆仑中三叠世闹仓坚沟组火山岩与晚三叠世鄂拉山组火山岩为研究对象,重点研究其岩石学、锆石U-Pb年代学和锆石微量元素地球化学,以期为揭示东昆仑三叠纪岩浆-构造演化过程提供关键证据。闹仓坚沟组火山岩主要以英安岩为主,而鄂拉山组则主要以流纹岩和安山岩为主。年代学研究结果表明,闹仓坚沟组英安岩形成于中三叠世(249~243 Ma),鄂拉山组流纹岩和安山岩形成于晚三叠世(221~219 Ma)。中三叠世英安岩样品的锆石可划分为低Ti(1.42×10-6~4.83×10-6)和高Ti(3.25×10-6~72.5×10-6)两类,前者具有较低的稀土元素含量(561×10-6 ~1 190×10-6),后者具有较高的稀土元素含量(1 817×10-6~6 236×10-6)。晚三叠世安山岩的岩浆锆石具有相对较高的Ti含量(11.3×10-6~31.2×10-6)和较低的稀土元素含量(∑REE=312×10-6~1 107×10-6),而晚三叠世流纹岩则具有较低的Ti(1.70×10-6~8.58×10-6)和稀土元素含量(355×10-6~1 670×10-6)。锆石成因分析揭示,中三叠世英安岩的高Ti锆石为热液成因,而中三叠世低Ti锆石和晚三叠世锆石则为典型岩浆成因。锆石Ti温度计与地壳厚度研究表明,东昆仑造山带于243~219 Ma期间发生了显著的岩浆温度升高和大陆地壳加厚作用。综合区域地质资料,本文认为东昆仑造山带经历了中三叠世古特提斯洋壳持续俯冲与晚三叠世碰撞后地壳加厚作用,东昆仑造山带并未发生明显的三叠纪岩石圈减薄作用。研究还表明,锆石微量元素组成并不能准确揭示造山带长英质岩浆岩的大地构造环境,建议慎重使用。

    Abstract:

    The Triassic volcanic rocks in the East Kunlun Orogenic Belt (EKOB) hold valuable magmatic-tectonic information, serving as a crucial probe to investigate the processes of the Paleo-Tethys orogeny. This study focuses on the Middle Triassic Naocangjiangou Formation and the Late Triassic Elashan Formation volcanic rocks, emphasizing petrology, zircon U-Pb geochronology, and zircon trace elements geochemistry to provide key evidence for the magmatic-tectonic evolution of the EKOB during the Triassic. The Naocangjiangou Formation is predominantly composed of dacites, while the Elashan Formation primarily consists of rhyolites and andesites. Geochronological results indicate that the dacites of the Naocangjiangou Formation formed during the Middle Triassic (249~243 Ma), whereas the rhyolites and andesites of the Elashan Formation formed in the Late Triassic (221~219 Ma). Zircons from the Middle Triassic dacites can be classified into two types based on Ti content: low-Ti (1.42×10-6 to 4.83×10-6) and high-Ti (3.25×10-6 to 72.5×10-6). The low-Ti zircons exhibit lower rare earth element (REE) contents (561×10-6 to 1 190×10-6), while the high-Ti zircons have higher REE contents (1 817×10-6 to 6 236×10-6). Late Triassic andesitic magmatic zircons show relatively high Ti contents (11.3×10-6 to 31.2×10-6) and lower REE contents (∑REE = 312×10-6 to 1 107×10-6), whereas Late Triassic rhyolitic zircons exhibit lower Ti contents (1.70×10-6 to 8.58×10-6) and REE contents (355×10-6 to 1 670×10-6). Zircon genesis analysis reveals that the high-Ti zircons in the Middle Triassic dacites are hydrothermal in origin, while the low-Ti zircons from the Middle Triassic and all Triassic zircons from the Late Triassic are of typical magmatic origin. Zircon Ti thermometry and crustal thickness studies indicate a significant increase in magmatic temperatures and crustal thickening in the EKOB between 243 Ma and 219 Ma. Synthesizing regional geological data, this study concludes that the EKOB experienced continuous subduction of the Paleo-Tethyan oceanic crust during the Middle Triassic, followed by crustal thickening due to collision in the Late Triassic. Notably, no significant lithospheric thinning occurred in the EKOB during the Triassic. This research further demonstrates that zircon trace element compositions cannot reliably reveal the tectonic settings of felsic magmatic rocks in orogenic belts, underscoring the need for cautious application of this method.

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赵昱杰,熊富浩,闫东东, 2025. 东昆仑三叠纪两期长英质火山活动的时代与动力学背景——来自锆石U-Pb年代学和地球化学的约束[J]. 岩石矿物学杂志, 44(5):1028~1050.
ZHAO Yu-jie, XIONG Fu-hao, YAN Dong-dong, 2025. Ages and tectonic settings of two episodic Triassic felsic volcanism in the East Kunlun: Constraints from zircon U-Pb geochronology and geochemistry[J]. Acta Petrologica et Mineralogica, 44(5): 1028~1050.

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  • 收稿日期:2024-11-19
  • 最后修改日期:2025-06-24
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  • 在线发布日期: 2025-11-21
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