Sr-Nd isotopic compositions of the Changjiang sediments: Implications for tracing sediment sources

来源 :Science in China(Series D:Earth Sciences) | 被引量 : 0次 | 上传用户:w4444w4444
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The suspended particulate and fine-grained floodplain sediments were collected from the main stream and tributaries of the Changjiang River for Sr-Nd isotopic measurements. The εNd(0) values gradually decrease downstream from -10.8 on average in the upper reaches to -12.3 in the lower reaches, whereas the 87Sr/86Sr ratios increase correspondingly, averaging 0.721899 and 0.725826 respectively in the upper and middle-lower reaches. The compositional variations primarily reflect the complex con- trols of provenance rocks, chemical weathering, and sediment characters between different catchments, among which the abnormal Sr-Nd isotopic compositions of the Yalong, Fujiang, Tuojiang and Yuanjiang rivers indicate the sediment provenance contributions from the Emeishan Basalt in the upper reaches and the old metamorphic and siliceous rocks in the middle-lower reaches. The Sr-Nd isotopic ratios of the Changjiang sediments can better reflect the average composition of weathered continental crust compared to other major rivers in the world because of the unique source rock types in the Changjiang drainage basin. The recognition of the Sr-Nd isotopic systematics of the Changjiang sediments will contribute to our understanding of the Changjiang evolution history and continental weathering processes during the Cenozoic, and also to reconstructing the paleoenvironmental changes in East China and the marginal seas. The suspended particulate and fine-grained floodplain sediments were collected from the main stream and tributaries of the Changjiang River for Sr-Nd isotopic measurements. The εNd (0) values ​​could gradually decrease from -10.8 on average in the upper reaches to -12.3 in the lower reaches, while the 87Sr / 86Sr ratios increase correspondingly, averaging 0.721899 and 0.725826 respectively in the upper and middle-lower reaches. The compositional states reflect the complex con- trols of provenance rocks, chemical weathering, and sediment characters between different catchments , among which the abnormal Sr-Nd isotopic compositions of the Yalong, Fujiang, Tuojiang and Yuanjiang rivers indicate the sediment provenance contributions from the Emeishan Basalt in the upper reaches and the old metamorphic and siliceous rocks in the middle-lower reaches. The Sr- Nd isotopic ratios of the Changjiang sediments can better reflect the average composition of weathered continental crus t compared to other major rivers in the world because of the unique source rock types in the Changjiang drainage basin. The recognition of the Sr-Nd isotopic systematics of the Changjiang sediments will contribute to our understanding of the Changjiang evolution history and continental weathering processes during the Cenozoic, and also to reconstructing the paleoenvironmental changes in East China and the marginal seas.
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