| 长江上游水系沉积物锶-钕同位素组成及物源示踪 |
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| 引用本文： | 邵,磊,李长安,张玉芬,袁胜元,王节涛,江华军,赵举兴.长江上游水系沉积物锶-钕同位素组成及物源示踪[J].沉积学报,2014,32(2):290-295. |
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| 作者姓名： | 邵 磊 李长安 张玉芬 袁胜元 王节涛 江华军 赵举兴 |
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| 作者单位： | 中国地质调查局武汉地质调查中心;中国地质大学(武汉)地球科学学院;中国地质大学(武汉)生物地质与环境地质国家重点实验室;中国地质大学(武汉)地球物理与空间信息学院;许昌学院城市与环境学院; |
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| 基金项目： | 国家自然科学基金(批准号:40971008,40771213);中国科学院地球环境研究所黄土与第四纪地质国家重点实验室开放基金(编号:SKLLQG0908)联合资助 |
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| 摘 要： | 泥沙资料表明，现代长江干流沉积物主要源自上游地区。因此，长江上游干支流沉积物主控关系及其源汇过程在长江水系沉积物物源示踪研究中极为重要。为探讨上述过程，详细测定了上游水系沉积物Sr-Nd同位素组成。结果显示，金沙江及闽江沉积物具有较高的εNd(0)值，主要受控于流域内大面积分布的峨眉山玄武岩的高εNd(0)背景值；嘉陵江水系沉积物具有相对较低的εNd(0)值，反映了其流域内源岩对沉积物Nd同位素组成的控制；与Nd同位素组成相比，水系沉积物87Sr/86Sr值具有更大的变化范围，表明除源岩因素外，沉积物Sr同位素组成受更为复杂的因素制约。支流与干流沉积物Sr-Nd同位素组成对比表明，长江上游干流沉积物主要来源于金沙江流域内的源岩，金沙江流域内的表壳岩系主导了上游干流沉积物的Sr-Nd同位素组成。
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| 关 键 词： | 长江 上游河段 锶- 钕同位素 物源示踪 |
Sr-Nd Isotopic Compositions of the Upper Yangtze River Sediments: Implications for Tracing Sediment Sources |
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| Abstract: | The Yangtze River is one of the major rivers in the world. Originating from the Tibetan Plateau, the river flows eastward across the three major topographic levels. Its drainage covers more than one- fifth of the continental area of China before finally entering the East China Sea. The huge Yangtze drainage basin is more than 6300 km in length and has a catchment area of 1.8×106km2. It is located between 24°27′~35°44′ N and 90°33′~122°19′ E. The Yangtze drainage basin spans the regional structure of China with three-grade relief and can be divided into three parts, the upper, middle and lower reaches. Although study of the evolution of the Yangtze River has a long history of more than 100 years, it is still controversial. Previous studies proposed that the Yangtze River can be dated back to the Cretaceous or the early Tertiary, the early Quaternary or the late Pleistocene. The source to sink process of the modern river sediments played a fundamental role in the research of the evolution of the Yangtze River. Sediments of the modern Yangtze River were mostly derived from the upper Yangtze drainage basin. Therefore, the erosion process of sediments from the upper Yangtze River played an important role in the erosion process of sediments from the whole river drainage system. The Sr-Nd isotopes have been proved to be rarely influenced by weathering, sediment transport and deposition process, especially the Nd isotope. We have reported the geochemical and Neodymium isotopic compositions of the late Cenozoic sediments in the Jianghan Basin to decipher information on the changing provenance and provide more constraints on the evolution of the Yangtze River. In this study, the fine-grained samples were collected from the main stream and tributaries (the Jinshajiang River, the Minjiang River and the Jialingjiang River) of the upper Yangtze River for Sr-Nd isotopic measurements. The results revealed that samples collected from the Jinshajiang River and the Minjiang River show high εNd(0) values. Although the source rocks in the Yangtze drainage basin are complicated including Archean metamorphic rocks, Paleozoic carbonate and sedimentary rocks, Mesozoic-Cenozoic igneous and clastic rocks, and Quaternary detrital sediments. It indicates that the influence of the large Emeishan Basalt Province is widely distributed in the upper Yangtze River valley in the Yunnan and Sichuan provinces. During the humid and warm climate, it undergoes rapid chemical weathering and the higher εNd(0) values could dominate the Nd isotopic compositions of the Yangtze River sediments. Samples from the Jianglingjiang River sediments show much lower εNd(0) values, indicating that the average Nd isotopic values of the source rocks in the Jialingjiang valley is much lower. Compared with Nd, the Sr isotopic values show a wider range, indicating that the Sr isotopic sediments of sediments are affected by much more complicated factors. In order to better understand how the modern Yangtze River generated sediments, we also collected the Sr Nd isotopic values reported by other researchers. The results have revealed that sediments from the main stream can be divided into two parts. One part of the sediments is characterized by high εNd (0) values and low 87Sr/86Sr values. The other part of the sediments is characterized by low εNd(0) values and high 87Sr/86Sr values. However, we find that both of these sediments were located in the same area with the samples collected from the Jinshajiang River (No matter from this study or previous studies). It indicates that these sediments were mainly derived from source rocks distributed in the Jinshajiang valley. The influence of the sediments from the Jialingjiang River could be excluded. However, this was not consistent with the information provided by the Changjiang (the Yangtze River) Sediment Bulletin that the Jialingjiang River is an important sediment supplier to the mainstream. |
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