Sr-Nd isotope geochemistry of eolian dust of the arid-semiarid areas in China: Implications for loess provenance and monsoon evolution  

作　　者：RAO Wenbo YANG Jiedong CHEN Jun LI Gaojun 

机构地区：[1]Department of Earth Sciences, Nanjing University, Nanjing 210093, China

出　　处：《Chinese Science Bulletin》2006年第12期1401-1412,共12页

摘　　要：Minerals and rocks have distinct 87Sr/86Sr and 143Nd/144Nd ratios, depending on their geological origin and ages, and these isotope ratios are less altered than elemental composition during transport in the atmosphere or after deposition as sediments, thus stable isotopes of Sr and Nd have great potential as tracers for provenance and trans- port of materials. During the hypergene process, Sr isotope ratios of sediments are controlled by their parent rocks, particle sizes and chemical weathering. In general, the higher the Sr isotope ratios of parent rocks, and/or the more the fine-grained fractions, and/or the stronger the chemical weathering, thus the higher the Sr isotope ratios of sediments. On the contrary, there are lower Sr isotope ratios of sedi- ments. Nd isotope ratios of sediments, independent of their particle sizes and chemical weathering, are only associated with parent rocks. For the prove- nance of the Chinese Loess Plateau, different re- seachers drew discordant and even contradictory conclusions by using the method of Sr-Nd isotopic tracing. From the previous Nd isotope data, it is con- sidered that the Tarim Basin, deserts in the central and west parts of Inner Mongolia and the Tibetan Plateau are the main sources of the Chinese Loess Plateau, and are also manufacturers for eolian dust of the Far East regions, together with the Chinese Loess Plateau. Sr isotope ratios of eolian dust are solely affected by wind sorting and weather- ing-pedogenesis due to its homogeneous composi- tion in the Chinese Loess Plateau. Wind sorting isrelated to the East Asian winter monsoon but weath- ering-pedogenesis is mainly associated with the East Asian summer monsoon. Studies on Sr isotopic compositions of the loess-paleosol sequence suggest that 87Sr/86Sr ratios in acid-soluble materials are an index for chemical weathering intensity of the Chi- nese Loess Plateau, indicating the East Asian sum- mer monsoon variations, whereas 87Sr/86Sr ratios in acid-insoluble materials are significantly controlled by particlMinerals and rocks have distinct ^87Sr/^86Sr and ^143Nd/^144Nd ratios, depending on their geological origin and ages, and these isotope ratios are less altered than elemental composition during transport in the atmosphere or after deposition as sediments, thus stable isotopes of Sr and Nd have great potential as tracers for provenance and transport of materials. During the hypergene process, Sr isotope ratios of sediments are controlled by their parent rocks, particle sizes and chemical weathering. In general, the higher the Sr isotope ratios of parent rocks, and/or the more the fine-grained fractions, and/or the stronger the chemical weathering, thus the higher the Sr isotope ratios of sediments. On the contrary, there are lower Sr isotope ratios of sediments. Nd isotope ratios of sediments, independent of their particle sizes and chemical weathering, are only associated with parent rocks. For the provenance of the Chinese Loess Plateau, different reseachers drew discordant and even contradictory conclusions by using the method of Sr-Nd isotopic tracing. From the previous Nd isotope data, it is considered that the Tarim Basin, deserts in the central and west parts of Inner Mongolia and the Tibetan Plateau are the main sources of the Chinese Loess Plateau, and are also manufacturers for eolian dust of the Far East regions, together with the Chinese Loess Plateau. Sr isotope ratios of eolian dust are solely affected by wind sorting and weathering-pedogenesis due to its homogeneous composition in the Chinese Loess Plateau. Wind sorting is related to the East Asian winter monsoon but weathering-pedogenesis is mainly associated with the East Asian summer monsoon. Studies on Sr isotopic compositions of the Ioess-paleosol sequence suggest that ^87Sr/^86Sr ratios in acid-soluble materials are an index for chemical weathering intensity of the Chinese Loess Plateau, indicating the East Asian summer monsoon variations, whereas ^87Sr/^86Sr ratios in acid-insoluble materials are significantly controlled by particle sizes, an

关 键 词：锶-钕同位素 季风 黄土 干旱-半干旱地区 地球化学 

分 类 号：P595[天文地球—地球化学]