北祁连北大河沉积物碎屑组成及物源正演分析——对物源定量分析方法的启示

Detrital Composition and Provenance Forward Modeling of Sediments in the Beida River,North Qilian:Implications for Quantitative Provenance Analysis

开展现代河流沉积物的物源分析正演研究,对厘清河流搬运分选过程对不同碎屑成分的影响、不同源区对汇区沉积物的贡献机制以及物源定量分析具有重要意义。对北祁连北大河与洪水坝河现代河流沉积物的物源开展了正演研究,结合砾石成分统计、重矿物分析和碎屑锆石U-Pb测年方法,分析了流域内不同物源对现代河流不同碎屑成分贡献的差异性。结果表明,两条河流沉积物的特征显示汇区不同碎屑成分对物源区岩性的反映各有侧重。其中砾石岩性能够反映整个流域的主要岩性;砂粒中的重矿物组合也可以反映源区主要岩性,且对重矿物含量较高的岩体或地层(如铁矿)十分敏感;碎屑锆石年龄谱反映了整个流域物源端元锆石的综合贡献,各年龄峰锆石占比与源区各年龄峰锆石贡献呈较好的正相关关系,其中源区沉积岩碎屑锆石的贡献比较显著。通过河流物源正演分析进一步建立现代河流源汇模式是实现物源量化分析的一个可行方向。

The forward modeling of provenance analysis for modern river sediments is important for clarifying the im⁃pact of river transportation and sorting processes on different debris components,the contribution mechanism of dif⁃ferent source regions to the sediments in the catchment area,and the quantitative analysis of provenance.In this study,through forward modeling of the modern river sediment sources of the Beida and Hongshuiba rivers in the North Qilian Mountains,we analyzed the difference of contribution of different sources to different detrital compo⁃nents of modern rivers in the basin by combining gravel composition statistics,heavy mineral analysis,and detrital zircon U-Pb dating methods.The characteristics of the sediments from the two rivers show that different clastic compo⁃nents in the catchment area vary in emphasis on the reflection of the lithology of the source area,and the gravel rock statistics reflects the main lithology of the entire basin.The heavy mineral assemblage in the sand can also reflect the main lithology of the source area and is sensitive to the rock mass or stratum(such as iron ore)with high contents of certain heavy minerals.The detrital zircon age spectrum reflects the comprehensive contribution of zircons from source strata in the whole drainage area,including the recycling of a large number of detrital zircons from sedimenta⁃ry rocks.The proportion of zircon in each age peak also has a good positive correlation with the contribution of zircon in each age peak in the source area.Forward modelling of the source to sink in modern river sediments gives a promis⁃ing direction for future quantitative provenance analysis.