| 小兴安岭河流沉积物源的异质性——重矿物与碎屑锆石U-Pb年代学约束 |
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| 引用本文：张冲,孙磊,王艳茹,谢远云,魏振宇,刘海金,汪烨辉,祁昊东,吴鹏,张艳.2026.小兴安岭河流沉积物源的异质性——重矿物与碎屑锆石U-Pb年代学约束[J].地球学报,47(4):868-884. |
| DOI：10.3975/cagsb.2026.042211 |
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| 基金项目:本文由黑龙江省自然科学基金项目(编号: ZD2023D003)、国家自然科学基金项目(编号: 42171006)和哈尔滨师范大学学术创新项目(编号: XKB202314)联合资助。 |
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| 中文摘要:河流沉积物蕴含丰富的源区地质信息, 深入解析其组成特征对揭示物源属性及搬运-沉积过程的控制机制具有重要意义。小兴安岭地区复杂的构造-岩浆演化历史为探究河流沉积物“源-汇”过程提供了理想窗口。本文选取呼兰河、岔林河、巴兰河和汤旺河现代河流沉积物为研究对象, 开展重矿物组成与碎屑锆石LA-ICP-MS U-Pb定年分析, 系统揭示了物源组成特征及其对区域构造-岩浆事件的响应。此外, 通过碎屑锆石可再现性分析, 讨论利用碎屑锆石年龄重建区域构造-岩浆事件的可靠性与稳定性。结果表明: (1)重矿物组成显示角闪石、绿帘石和钛铁矿含量存在空间差异, 主要受控于源区母岩类型及出露面积, 构造-热事件强度、水动力分选与物源稀释作用亦有影响; (2)碎屑锆石年龄谱识别出三组峰值: ~190 Ma(230~100 Ma)、~250 Ma(300~230 Ma)和~470 Ma(500~400 Ma), 与小兴安岭构造-岩浆事件耦合, 证实显著的“源-汇”响应关系; (3)四条河流沉积物均以230~100 Ma锆石为主(占比66.67%~98.25%), 但汤旺河早古生代锆石(500~400 Ma)占比(15.32%)显著高于呼兰河(4.27%)、岔林河(5.74%)及巴兰河(0.88%), 其空间分异与流域内同时代基岩出露面积有关; (4)基于T和K模型的可再现性分析表明, 低频周期的碎屑锆石对火成岩源区信号的可再现性优于高频周期; (5)锆石年龄峰值明确记录区域构造事件: ~470 Ma响应古亚洲洋俯冲作用, ~250 Ma对应古亚洲洋最终闭合, ~190 Ma同时关联蒙古—鄂霍茨克洋消减与古太平洋板块初始俯冲。本研究证实, 在小兴安岭小型河流系统中, 重矿物与碎屑锆石U-Pb年代学能有效示踪源区母岩属性及其空间异质性, 且低频周期下的河流碎屑锆石可以用于重建源区构造-岩浆事件。然而, 物源解释需综合考虑母岩分布、水动力条件及沉积混合效应等多重因素。在母岩组成复杂或沉积过程存在显著粒度效应的河流系统中, 需结合多指标证据进行综合物源解析。 |
| 中文关键词:小兴安岭 河流沉积物 物源示踪 重矿物 碎屑锆石U-Pb年代学 |
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| Heterogeneity of Sediment Sources in Rivers of the Lesser Xing’an Range: Constraints from Heavy Minerals and Detrital Zircon U-Pb Geochronology |
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| Abstract:River sediments preserve abundant geological information about their source regions. A detailed analysis of their compositional characteristics is crucial for understanding provenance signatures and the controlling mechanisms of sediment transport and deposition. The complex tectonic and magmatic evolution of the Lesser Xing’an Range offers an ideal natural laboratory for investigating the “source-to-sink” processes of river sediments. In this study, modern sediments from the Hulan, Chalin, Balan, and Tangwang Rivers were analyzed. Heavy mineral composition, detrital zircon LA-ICP-MS U-Pb geochronology were employed to systematically investigate provenance characteristics and their responses to regional tectonic-magmatic events. Additionally, the reliability and stability of detrital zircon age data in reconstructing such events were evaluated through reproducibility analyses.The results demonstrate the following: (1) Heavy mineral assemblages exhibit spatial variations in amphibole, epidote, and ilmenite contents, primarily governed by the lithological composition and exposure of source rocks, with additional influences from tectonothermal intensity, hydrodynamic sorting, and provenance dilution; (2) Detrital zircon age spectra reveal three prominent age groups: ~190 Ma (230–100 Ma), ~250 Ma (300–230 Ma), and ~470 Ma (500–400 Ma), which correspond to major tectonic-magmatic events in the Lesser Xing’an region, confirming a strong source-to-sink coupling; (3) Sediments from all four rivers are predominantly composed of 230–100 Ma zircons (66.67%–98.25%), while the proportion of Early Paleozoic zircons (500–400 Ma) in the Tangwang River (15.32%) is significantly higher than in the Hulan (4.27%), Chalin (5.74%), and Balan (0.88%) Rivers. This spatial variability is attributed to the differing exposures of coeval bedrock within the drainage basins; (4) Reproducibility analysis based on T and K models indicates that detrital zircons from low-frequency depositional cycles exhibit higher fidelity in recording igneous source signals compared to those from high-frequency cycles; (5) The identified zircon age peaks effectively record regional tectonic events: ~470 Ma is associated with subduction of the Paleo-Asian Ocean, ~250 Ma corresponds to its final closure, and ~190 Ma reflects both the subduction of the Mongol–Okhotsk Ocean and the initiation of Paleo-Pacific Plate subduction.This study confirms that in the small river systems of the Lesser Xing’an Mountains, heavy mineral assemblages and detrital zircon U-Pb geochronology serve as effective proxies for tracing source rock characteristics and spatial heterogeneity. Furthermore, detrital zircons from low-frequency cycles may serve as reliable indicators for reconstructing tectonic-magmatic events in the source region. However, provenance interpretation must consider a range of factors, including the distribution of parent rocks, hydrodynamic conditions, and sediment mixing processes. In systems with complex lithological compositions or significant grain-size sorting effects, a multi-proxy approach to provenance analysis is essential. |
| keywords:Lesser Xing’an Range river sediments provenance tracing heavy minerals detrital zircon U-Pb geochronology |
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