现代河流碎屑磷灰石原位地球化学分析——对长江物源示踪研究的启示

长江是连接青藏高原和西太平洋的东亚最大河流，研究其源汇过程对于认识和理解沉积物剥蚀、搬运和沉积过程等方面具有重要科学意义。对河流沉积物中常见的磷灰石开展了原位微量元素和87Sr/86Sr比值分析，结果表明，金沙江的微量元素和87Sr/86Sr比值二维散点图的分布区域与大渡河、岷江和嘉陵江的明显不同；丰都段长江干流样品与大渡河、岷江和嘉陵江样品形成重叠区域，结合MDS（非矩阵多维标度）判断图结果，说明丰都段长江干流的物质主要来自龙门山。磷灰石原位地球化学分析方法可以有效区分发源于青藏高原东南的金沙江和发源于龙门山的大渡河、岷江和嘉陵江的物质。但由于金沙江梯级水电站的建设对其下游沉积物的组成起到重要影响，在今后使用该方法进行长江全流域物源示踪研究时需要谨慎。

In-situ Geochemical Analysis of Modern Fluvial Detrital Apatite: Implications for provenance tracing studies in the Yangtze River

The Yangtze River is the largest river in East Asia， connecting the Tibetan Plateau and the western Pacific Ocean. The study of its source and sink process is of great scientific significance for understanding the processes of sediment denudation， transport and deposition. In situ analysis of trace elements and 87Sr/86Sr ratios in apatite commonly found in river sediments found from a two-dimensional scatter plot that the distribution area of the Jinsha River was significantly different from that of the Dadu， Minjiang and Jialing Rivers. The Yangtze River mainstream samples in the Fengdu section overlap with those from the Dadu， Minjiang and Jialing Rivers. When combined with the results from a multidimensional scaling （MDS） judgement chart， it was indicated that the material in the main stream of the Yangtze River in the Fengdu Section mainly comes from the Longmen Mountain. The in situ geochemical analysis of apatite effectively distinguished the materials originating from the Jinsha River in the southeastern Tibetan Plateau and from the Dadu， Minjiang and Jialing Rivers in the Longmen Mountain. This provides a better reference for future provenance-tracing studies of the whole Yangtze River Basin. However， due to the important influence of current construction of the Jinsha River cascade hydropower station on the composition of its downstream sediment， caution should be exercised when applying this method in such future studies.