Abstract Magnetite is typomorphic, and its crystal textures and chemical fingerprint form unique signatures that can be used to determine sediment provenance. Determination of the provenance of sediments in the upper Yangtze River is critical for understanding its evolution and the uplift of the Tibetan Plateau. In this study, petrographic analysis and electron-probe microanalysis (EPMA) of 800 detrital magnetite grains were performed to differentiate the provenance of sediments within the mainstream and major tributaries of the upper Yangtze River catchment. Chemical analyses show that the elemental composition of magnetite grains shows pronounced variations among the different sections of the mainstream and tributaries. Based on the observed chemical fingerprints, we infer that the source rocks control the elemental composition of magnetite grains. The magnetite contribution is closely related to the tectonics, climate, and erosion of parent rocks within different drainage basins. Magnetite from the trunk stream of the Jinsha River is found to be a significant contributor to the upper Yangtze River. Magnetite grains of the upper Jinsha River are primarily derived from source areas composed of silicic plutonic rocks and ophiolite lithologies that crop out on the SE Tibetan Plateau. Magnetite grains within the sands of the lower Jinshajiang sediments are characterized by high concentrations of Ti, Mg, Cr, Al, and Mn, and are derived from the widely distributed Emeishan flood basalts and Pan-Xi layered basic–ultrabasic igneous rocks. This source is also a major contributor of magnetite to the upper Yangtze River, and the parent rock distributed in this region is of typomorphic significance to the development of the Yangtze River. The origin of magnetite grains in the tributaries depends on the parent rocks distributed in their catchments. In summary, the presence of detrital magnetite grains provides valuable information for discriminating the provenance of sediments in the upper Yangtze River drainage basins.

中文翻译：

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长江上游流域沉积物物源判别：重矿物特征和碎屑磁铁矿地球化学的新见解

摘要 磁铁矿具有类型特征，其晶体结构和化学指纹形成独特的特征，可用于确定沉积物来源。确定长江上游沉积物的物源对于了解其演化和青藏高原的隆升至关重要。在这项研究中，对 800 颗碎屑磁铁矿颗粒进行了岩相分析和电子探针微量分析 (EPMA)，以区分长江上游流域干流和主要支流内沉积物的来源。化学分析表明，磁铁矿颗粒的元素组成在干流和支流不同断面之间表现出明显的变化。根据观察到的化学指纹，我们推断烃源岩控制着磁铁矿颗粒的元素组成。磁铁矿的贡献与不同流域内母岩的构造、气候和侵蚀密切相关。金沙江干流的磁铁矿被发现是长江上游的重要贡献者。金沙江上游磁铁矿颗粒主要来自青藏高原东南部出露的硅质深成岩和蛇绿岩岩性组成的源区。金沙江下游沉积物砂中的磁铁矿颗粒以高浓度的 Ti、Mg、Cr、Al 和 Mn 为特征，来源于广泛分布的峨眉山溢流玄武岩和盘西层状基性-超基性火成岩。该源也是长江上游磁铁矿的主要贡献者，分布于该地区的母岩对长江的发育具有类型形态意义。支流中磁铁矿颗粒的成因取决于其流域中分布的母岩。总之，碎屑磁铁矿颗粒的存在为区分长江上游流域沉积物的物源提供了有价值的信息。