基于碎屑锆石特征的雅鲁藏布江山南宽谷风成沙丘物源示踪  

PROVENANCE ANALYSIS OF WIND-FORMED DUNES IN THE SHANNAN BROADVALLEYOFTHE YARLUNGZANGBORIVERBASED ON DETRITAL ZIRCON CHARACTERISTICS

作　　者：马晓莉 李顺[1] 岳雅慧[2] MA Xiaoli;LI Shun;YUE Yahui(School of Oceanography,Shanghai Jiao Tong University,Shanghai 200030;Institute of Tibetan Plateau Research,Chinese Academy of Sciences,Beijing 100101)

机构地区：[1]上海交通大学海洋学院,上海200030 [2]中国科学院青藏高原研究所,北京100101

出　　处：《第四纪研究》2023年第5期1157-1171,共15页Quaternary Sciences

基　　金：国家自然科学基金项目(批准号:42272237);上海市极地前沿科学研究基地经费共同资助。

摘　　要：雅鲁藏布江河谷(尤其是“一江两河”区域)风沙化较为严重,制约了当地社会经济的可持续发展,追踪河谷风沙来源对当地风沙治理意义重大。本研究聚焦于拉萨贡嘎机场附近的山南宽谷风沙地貌,采集2个河沙、 3个风成沙丘和1个坡积物样品,以及引用前人研究的2个河沙样品。基于碎屑锆石U-Pb年龄及微量元素地球化学特征,进行沙源示踪研究,旨在为当地风沙治理提供科学依据。对360颗锆石进行LA-ICP-MS U-Pb定年,获得322个谐和年龄。分析结果表明,河沙、风成沙丘及坡积物样品碎屑锆石U-Pb年龄分布特征高度相似,主要峰值与冈底斯岩浆弧新生代的两期岩浆活动一一对应;非矩阵多维标度统计技术(MDS)分析也证实了样品与冈底斯岩浆弧有良好的亲缘性;地球化学判别图解显示锆石具有亏损轻稀土元素、富集重稀土元素、明显正Ce异常和明显负Eu异常的特征,亦指示其岩浆成因,表明冈底斯岩浆弧为沙丘、河沙与坡积物中碎屑锆石的主要来源。依据不同类型样品碎屑锆石年龄对比以及锆石年龄相似程度对比,结果发现:1)雅鲁藏布江地区风沙地貌主要是由于枯水季河床水位下降,导致河岸和河漫滩出露地表,就地起沙吹扬到山坡上所形成;2)研究区河沙并非主要从上游搬运而来,更多是拉萨河搬运汇入的泥沙。依据沙源分析结果,欲解决河谷风沙化问题,首要应在河岸和河漫滩种植适宜当地气候的耐旱植物固定河床上的泥沙,这是最直接有效的手段。The Yarlung Zangbo River valley,especially the area of‘the mainstream and its two tributaries',is experiencing severe wind erosion and desertification,which restricts the sustainable development of local society and economy.Tracing the provenance of wind-borne sand in the river valley is significant for local aeolian desertification control.This study focuses on the aeolian landforms(29°19'~29°21'N,90°41'~91°08'E)in the wide valley of Shannan District around the Gonggar Airport.Two river sand samples(TYO2 and TY04),three aeolian dune samples(TY01,TY03 and TY06),and one slope deposit sample(TY05)were collected,while two river sand samples(AY06-28-06-(1)and AY09-08-08-7)from published articles were cited.Combing detrital zircon U-Pb geochronology and trace element geochemistry,we try to trace the provenance of aeolian dunes to provide a scientific basis for local aeolian desertification control.LA-ICP-MS U-Pb dating of 360 zircon grains yielded 322 concordant ages.The results show that detrital zircon U-Pb age distributions of the river sand,aeolian dune and slope deposit samples are highly similar.The main peaks match well with the two episodes of magmatism in the Cenozoic Gangdese magmatic arc.Non-metric multidimensional scaling(MDS)analysis also confirms a strong affinity between the samples and the Gangdese magmatic arc.Geochemical discrimination diagrams indicate that the zircons are depleted in light rare earth elements(LREEs),enriched in heavy rare earth elements(HREEs),and exhibit positive Ce anomalies and negative Eu anomalies.These characteristics suggest a magmatic origin for the zircons and indicate that the Gangdese magmatic arc is the primary source of detrital zircons in the dunes,river sands,and slope deposits.Comparison of detrital zircon ages between different sample types and assessment of zircon age similarity reveals that aeolian landforms in the Yarlung Zangbo River region primarily result from exposure of shallow banks and river beaches due to low water levels in the dry season,with loc

关 键 词：雅鲁藏布江河谷 风沙地貌 物源分析 防风固沙 沙漠化 

分 类 号：P512.21[天文地球—地质学] P597.3